[Technical Field] [0001]
The present invention relates to a method for exchanging information between communication terminals and a 10 communication terminal and, in particular, to a method for
exchanging information such as node information and routing information between communication terminals on the basis of whether or not mutually corresponding node information and routing information entries exist, and such communication 1 5 terminal.
[Background Art] [0002]
As communication means in remote areas where network infrastructures are unavailable or at the time of disaster, 20 autonomous distributed (self-configuring) mobile ad-hoc
networks (MANET) have come to attention in recent years, in which data is forwarded from one communication terminal to another by wireless communication, and implementation of information sharing in a large-scale environment in which a 25 wide range of many communication terminals (nodes)
participate, as well as network infrastructures, is desired. [0003]
In order to share information among a wide range of many communication terminals in a mobile ad-hoc network (MANET),

2 especially the following two kinds of information need to be
shared among communication terminals in the network:
(1) Node information (i.e. node IDs, node IP addresses, and
information about contents held by nodes) and
5 (2) Routing information (i.e. next-hop (forwarding destination)
node information for reaching a destination node, the
probability of reaching the destination node, and the routing
address of the destination node).
[0004]
10 This is because the mobile ad-hoc network uses a
mechanism in which each communication terminal identifies an "information sharing terminal" with which the communication terminal is to communicate by "(1) node information" and identifies a "communication (data transfer) route" to the
15 aforementioned "information sharing terminal" by "(2) routing information". [0005]
Accordingly, each communication terminal (node) needs to be in a state where they manage "(1) node information"
20 relating to each of other communication terminals in a network and "(2) routing information" in association with each other or hold both kinds of information. [0006]
On the other hand, the amount of information exchanged
25 between communication terminals needs to be reduced because communication bandwidth available between communication terminals in a mobile ad-hoc network (MANET) is limited. In other words, since communication terminals in the mobile ad-hoc network (MANET) directly communicate with each other

3 by wireless communication, interference occurs between radio
waves from communication terminals that participate in the
network, thus limiting available communication bandwidth.
Furthermore, since communication radio waves can fail to reach
5 communication terminals due to movement of the
communication terminals or interruption of radio waves by
obstacles, the communication link between communication
terminals can often disconnected or network disruption can
occur.
10 [0007]
Consequently, communication bandwidth and time available to one communication terminal for communication with another communication terminal are limited. [0008]
15 In order to enable information sharing in a large-scale
environment in mobile ad-hoc networks (MANET) under these circumstances or delay/disruption tolerant networks (DTN) which cope with a poor-quality communication environment in which the network can be disrupted, a method is used in which
20 each communication terminal holds for some time node
information and routing information relating to a correspondent communication terminal with which the communication terminal was once connected in order to enable "(1) node information" and "(2) routing information" to be exchange
25 between many communication terminals. [0009]
For example, a communication terminal exchanges node information and routing information relating to every other communication terminal that the terminal has met or neighbored

4 and stores the information for a certain period of time in
methods for managing information in a delay/disruption
tolerant network (DTN) described in NPL 1, "Probabilistic
routing in intermittently connected networks" by Anders
5 Lindgren et al. (ACM SIGMOBILE Mobile Computing and
Communications Review, Volume 7, Issue 3, July 2003, Pages
19-20 and NPL 2, "ROUTING IN INTERMITTENTLY
CONNECTED MOBILE AD-HOC NETWORKS AND DELAY
TOLERANT NETWORKS: OVERVIEW AND CHALLENGES" by
10 ZHENSHENG ZHANG et al. (IEEE Communications Surveys & Tutorials, 1ST QUARTER 2006, VOLUME 8, NO. 1, Pages 24-37). Storing node information and routing information as a history for a certain period of time in this way enables a communication terminal to identify a next communication
15 terminal to which data is to be passed when a communication link is recovered or when the communication terminal meets another communication terminal. [0010]
However, the amount of information to be exchanged
20 between communication terminals increases in proportion to the number of communication terminals participating in the network. Given these circumstances, in order for communication terminals (nodes) to share information with each other in a mobile ad-hoc network (MANET) in which a
25 wide range of many communication terminals participate or a delay/disruption tolerant network (DTN), which is liable to network disruption, the amount of information exchanged between communication terminals (nodes) needs to be minimized to reduce load on communication bandwidth by

5 cleverly managing and exchanging node information and
routing information.
[001 1]
As described above, for information sharing in mobile
5 ad-hoc networks (MANET) or delay/disruption tolerant
networks (DTN), "(1) node information" and "(2) routing
information" needs to be managed in association with each
other or to be held, and the amount of exchanged information
relating to both "(1) node information" and "(2) routing
10 information" to be exchanged between communication terminals needs to be reduced. [0012]
However, existing network techniques, for example methods proposed in NPL 3, "Design Issues ofPeer-to-Peer
15 Systems for Wireless Ad Hoc Networks" by Dewan Tanvir
Ahmed et al. (Networking, 2007. ICN '07. Sixth International Conference on Date of Conference, Pages 22-28, April 2007) and NPL 4, "Scalable routing protocols for mobile ad-hoc networks" by Xiaoyan Hong (Network, IEEE Date of
20 Publication: Jul/Aug 2002, Volume: 16, Issue: 4, Pages 11-21) have not achieved a fundamental solution. In the methods, mechanisms for exchanging node information and routing information independently of each other are used and a network is layered and information is managed in a layered manner in
25 order to reduce the amount of information exchanged. [0013]
Specifically, in the existing network techniques, since the function of exchanging node information and the function of exchanging routing information operate independently in

6 different network layers and control focusing solely to one of
the node information and routing information is performed, the
node information and the routing information are not managed
or held in pairs. Consequently, a lag between a period in
5 which node information NlOO is exchanged and a period in
which routing information RlOO is exchanged occurs with the
other communication terminal (other node) as illustrated in Fig.
11. Fig. 11 is a diagram for illustrating the messaging
timings of providing node information and routing information
10 held by a communication terminal (node) and periods during which the communication terminal is holding the node information and routing information in an existing technique. Fig. 11 focuses on a node Y entry relating to node Y received from node X, i.e. a node information entry NlOOy, and a routing
15 information entry RlOOy out of the node information NlOO held by node A and the routing information RlOO held by node A and illustrates a situation where there are differences in the messaging timing of providing information to another node and in period in which the received information is held.
20 [0014]
Specifically, with regard to a node information entry NlOOy relating to node Y that is to be held by node A, for example, there is a period, depicted as node information non-holding period PI in Fig. 11, between receipt of the routing
25 information entry RlOOy from node X and receipt of the node information entry NlOOy from node X during which node A does not hold the node information entry NlOOy relating to node Y and the routing information entry RlOOy in pairs because of a difference between the periodicity of exchange of node

7 information NlOO and the periodicity of exchange of routing
information RIOO.
[0015]
Furthermore, because of a lag between a node information 5 NlOO holding period and a routing information RIOO holding period, the holding period of the routing information entry RlOOy of node Y, for example, may expire and the routing information entry RlOOy may be deleted, which may result in a period during which node A holds only the node information 10 entry NlOOy of node Y out of the two kinds of information
relating to node Y that are to be held by node A, as depicted as a routing information non-holding period P2 in Fig. 11. [0016]
When node A provides information to the other node at
15 messaging timing Tl and messaging timing T2 in Fig. 11, node
A does not provide the routing information entry RlOOy relating
to node Y and provides only the node information entry NlOOy
relating to node Y. As a result, communication bandwidth and
storage of the communication terminals are wasted.
20 [Citation List]
[Non Patent Literature] [0017]
[NPL 1] Anders Lindgren, Avri Doria Lule, Olov Schelen: "Probabilistic routing in intermittently connected networks", 25 ACM SIGMOBILE Mobile Computing and Communications Review, Volume 7, Issue 3, July 2003, Pages 19-20
[NPL 2] ZHENSHENG ZHANG, SAN DIEGO RESEARCH CENTER: "ROUTING IN INTERMITTENTLY CONNECTED MOBILE AD-HOC NETWORKS AND DELAY TOLERANT

8 NETWORKS: OVERVIEW AND CHALLENGES", IEEE
Communications Surveys & Tutorials, 1ST QUATER 2006,
VOLUME 8, NO. 1, Pages 24-37
[NPL 3] Dewan Tanvir Ahmed, Shervin Shirmohammadi: 5 "Design Issues ofPeer-to-Peer Systems for Wireless Ad Hoc Networks", Networking, 2007. ICN '07. Sixth International Conference on Date of Conference, Pages 22-28, April 2007
[NPL 4] Xiaoyan Hong: "Scalable routing protocols for mobile ad-hoc networks", Network, IEEE Date of Publication: 10 Jul/Aug 2002, Volume: 16, Issue: 4, Pages 11-21
[Summary of Invention]
[Technical Problem] [0018]
As described above, the existing network techniques 15 cannot solve the following problems. [0019]
A first problem is that when a communication terminal meets another communication terminal, the communication terminal can possibly provide only one of the node information 20 and routing information relating to a particular communication terminal. This is because the function of exchanging node information and the function of exchanging routing information operate independently of each other in different network layers and the timings of exchanging the two kinds of information are 25 not synchronized. As a result, the node information and the routing information relating to the particular communication terminal cannot be provided to the other communication terminal in pairs and communication bandwidth and resources of the communication terminals are wasted.

9 [0020]
A second problem is that a communication terminal can
possibly keep holding only one of node information and routing
information relating to a particular communication terminal.
5 This is because the function of managing node information or
the function of managing routing information is not capable of
determining whether a routing information entry or a node
information entry that corresponds to a node information entry
or a routing information entry exists or not to identify
10 information that does not need to be held. Consequently, node information and routing information for a particular communication terminal cannot be managed in pairs and communication bandwidth and resources of the communication terminals are wasted.
15 [0021]
Specifically, in information sharing among communication terminals in mobile ad-hoc networks (MANET) and delay/disruption tolerant networks (DTN), communication terminals needs to be placed in a "state where both of node
20 information and routing information are managed in association with each other or a state where both of the two kinds of information are held". However, because exchange of node information and exchange of routing information are controlled independently of each other, there are the following two
25 problems:
(1) there is a difference between the periodicity of exchange of node information and the periodicity of exchange of routing information and therefore there is periods in which communication terminals do not hold the two kinds of

10 information, node information and routing information, and
(2) there is a lag between a node information holding period and
a routing information holding period, which results in a period
in which only one of the two kinds of information is held.
5 Consequently, communication bandwidth and storages of the
communication terminals are wasted.
[0022]
(Objects of Invention)
The present invention has been made in light of these
10 problems and a first object of the present invention is to provide a method for exchanging information between communication terminals and a communication terminal that include a mechanism for acquiring both of a node information entry and a routing information entry that relate to a particular
15 communication terminal at substantially the same time. [0023]
A second object of the present invention is to provide a method for exchanging information between communication terminals and a communication terminal that include a
20 mechanism for avoiding uselessly holding only one of a pair of a node information entry and a routing information entry that relate to a particular communication terminal.
[Solution to Problem] 25 [0024]
To solve the problems described above, a method for exchanging information between communication terminals and a communication terminal according to the present invention primarily employ the following characteristic configurations.

11
[0025]
(1) A first method for exchanging information between
communication terminals according to the present invention is a
method for exchanging node information and routing
5 information between a plurality of communication terminals constituting a network, the node information being used for identifying each of the communication terminals, the routing information indicating a communication route to each of the communication terminals which is a destination; wherein when
10 each of the plurality of communication terminals detects, in the routing information locally held by the communication terminal, update of a routing information entry relating to any of the communication terminals or detects, in the node information locally held by the communication terminal, update of a node
15 information entry relating to any of the communication terminal, the communication terminal references, in the node information locally held by the communication terminal, a node information entry corresponding to the updated routing information entry or, references, in the routing information locally held by the
20 communication terminal, a routing information entry
corresponding to the updated node information entry; and if the corresponding node information entry or the corresponding routing information entry does not exist, acquires the corresponding node information entry or the corresponding
25 routing information entry from another communication terminal. [0026]
(2) A second method for exchanging information between
communication terminals according to the present invention is a

12 method for exchanging node information and routing
information between a plurality of communication terminals
constituting a network, the node information being used for
identifying each of the communication terminals, the routing
5 information indicating a communication route to each of the
communication terminals which is a destination; wherein when
each of the plurality of communication terminals determines
whether or not each of the routing information entries relating
to the communication terminals that are included in the routing
10 information locally held by the communication terminal or each of the node information entries relating to the communication terminals that are included in the node information locally held by the communication terminal is information to be held, the communication terminal references, in the node information
15 locally held by the communication terminal, a node information entry corresponding to each of the routing information entries or references, in the routing information locally held by the communication terminal, a routing information entry corresponding to each of the node information entries; and if a
20 node information entry corresponding to the routing
information entry does not exist, the communication terminal deletes the relevant routing information entry from the routing information locally held by the communication terminal, or if a routing information entry corresponding to the node
25 information entry does not exist, the communication terminal deletes the relevant node information entry from the node information locally held by the communication terminal. [0027]

13 (3) A third method for exchanging information between
communication terminals according to the present invention is a
method for exchanging node information and routing
information between a plurality of communication terminals
5 constituting a network, the node information being used for
identifying each of the communication terminals, the routing
information indicating a communication route to each of
communication terminals which is a destination; wherein when
each of the plurality of communication terminals determines
10 whether or not each of the routing information entries relating to the communication terminals that are included in the routing information locally held by the communication terminal or each of the node information entries relating to the communication terminals that are included in the node information locally held
15 by the communication terminal is information to be held, the communication terminal references, in the node information locally held by the communication terminal, a node information entry corresponding to each of the routing information entries or references, in the routing information locally held by the
20 communication terminal, a routing information entry
corresponding to each of the node information entries; and if a node information entry corresponding to the routing information entry does not exist, the communication terminal places the relevant routing information entry on an own list of
25 candidates to be deleted at the communication terminal, stores the own list of candidates to be deleted at the communication terminal, and sends the own list of candidates to be deleted at the communication terminal to another communication terminal as a list of candidates to be deleted at a correspondent

14 communication terminal, or if a routing information entry
corresponding to each of the node information entries does not
exist, places the relevant node information entry on an own list
of candidates to be deleted at the communication terminal,
5 stores the own list of candidates to be deleted at the
communication terminal, and sends the own list of candidates to
be deleted at the communication terminal to another
communication terminal as a list of candidates to be deleted at
a correspondent communication terminal; when the
10 communication terminal receives the list of candidates to be deleted at the correspondent communication terminal from another communication terminal, the communication terminal determines, on the basis of a combination of the routing information entry or the node information entry placed on the
15 received list of candidates to be deleted at the correspondent communication terminal and the routing information entry or the node information entry placed on the stored own list of candidates to be deleted at the communication terminal, whether or not each of the routing information entries locally
20 held by the communication terminal is to be kept held or
whether or not each of the node information entries locally held by the communication terminal is to be kept held; and the communication terminal deletes the routing information entry determined to be invalid information that does not need to be
25 kept held from the routing information locally held by the
communication terminal, or deletes the node information entry determined to be invalid information that does not need to be kept held from the node information held locally by the communication terminal.

15 [0028]
(4) A first communication terminal according to the present
invention is a communication terminal which exchanges node
information and routing information with one or more other
5 communication terminals constituting a network, the node
information being used for identifying each of a plurality of
communication terminals, the routing information indicating a
communication route to each of communication terminals which
is a destination, the communication terminal comprises at least
10 means for: upon detection of update of a routing information entry relating to any of the communication terminals in the routing information held by the communication terminal or update of a node information entry relating to any of the communication terminals in the node information held by the
15 communication terminal, referencing, in the node information held by the communication terminal, a node information entry corresponding to the updated routing information entry or, referencing, in the routing information held by the communication terminal, a routing information entry
20 corresponding to the updated node information entry; and if the corresponding node information entry or the corresponding routing information entry does not exist, acquiring the corresponding node information entry or the corresponding routing information entry from another communication
25 terminal. [0029]
(5) A second communication terminal according to the present invention is a communication terminal which exchanges node information and routing information with one or more other

16 communication terminals constituting a network, the node
information being used for identifying each of a plurality of
communication terminals, the routing information indicating a
communication route to each of communication terminals which
5 is a destination, the communication terminal comprises at least
means for: when determining whether or not each of the routing
information entries relating to the communication terminals
that are included in the routing information held by the
communication terminal or each of the node information entries
10 relating to the communication terminals that are included in the node information held by the communication terminal is information to be held, referencing, in the node information locally held by the communication terminal, a node information entry corresponding to each of the routing information entries
15 or referencing, in the routing information locally held by the communication terminal, a routing information entry corresponding to each of the node information entries; and if a node information entry corresponding to the routing information entry does not exist, deleting the relevant routing
20 information entry from the routing information locally held by the communication terminal, or if a routing information entry corresponding to the node information entry does not exist, deleting the relevant node information entry from the node information locally held by the communication terminal.
25 [0030]
(6) A third communication terminal according to the present invention is a communication terminal which exchanges node information and routing information with one or more other communication terminals constituting a network, the node

17 information being used for identifying eacli of a plurality of
communication terminals, the routing information indicating a
communication route to each of communication terminals which
is a destination, the communication terminal comprises at least
5 means for: when determining whether or not each of the routing
information entries relating to the communication terminals
that are included in the routing information held by the
communication terminal or each of the node information entries
relating to the communication terminals that are included in the
10 node information held by the communication terminal is
information to be held, referencing, in the node information held by the communication terminal, a node information entry corresponding to each of the routing information entries or referencing, in the routing information held by the
15 communication terminal, a routing information entry
corresponding to each of the node information entries; and if a node information entry corresponding to the routing information entry does not exist, placing the relevant routing information entry on an own list of candidates to be deleted at
20 the communication terminal, storing the own list of candidates to be deleted at the communication terminal, and sending the own list of candidates to be deleted at the communication terminal to another communication terminal as a list of candidates to be deleted at a correspondent communication
25 terminal, or if a routing information entry corresponding to
each of the node information entries does not exist, placing the relevant node information entry on an own list of candidates to be deleted at the communication terminal, storing the own list of candidates to be deleted at the communication terminal, and

18 sending the own list of candidates to be deleted at the
communication terminal to another communication terminal as a
list of candidates to be deleted at a correspondent
communication terminal; when the communication terminal
5 receives the list of candidates to be deleted at the
correspondent communication terminal from another
communication terminal, determining, on the basis of a
combination of the routing information entry or the node
information entry placed on the received list of candidates to
10 be deleted at the correspondent communication terminal and the routing information entry or the node information entry placed on the stored own list of candidates to be deleted at the communication terminal, whether or not each of the routing information entries held by the communication terminal is to be
15 kept held or whether or not each of the node information entries held by the communication terminal is to be kept held; and deleting the routing information entry determined to be invalid information that does not need to be kept held from the routing information held by the communication terminal, or deleting
20 the node information entry determined to be invalid information that does not need to be kept held from the node information held by the communication terminal.
[Advantageous Effect of Invention] 25 [0031]
The method for exchanging information between communication terminals and a communication terminal according to the present invention have the following advantageous effects.

19 [0032]
A first advantageous effect is that a node information
entry and a routing information entry that relate to a particular
communication terminal can be provided together to one or
5 more communication terminals. This is because the method
and the communication terminal have a mechanism that, when
node information or routing information is exchanged, checks
correspondences between node information entries and routing
information entries held by the communication terminal and, if
10 any of the node information entries or routing information entries is missing, acquires the missing information from another communication terminal. [0033]
A second advantageous effect is that the communication
15 terminal can hold entries of both of node information and routing information relating to a particular communication terminal in pairs. This is because the method and the communication terminal have a mechanism that checks correspondences between node information entries and routing
20 information entries held by the communication terminal and, if any of the node information entries and the routing information entries is missing, deletes a node information entry or routing information entry that does not have a corresponding entry.
25 [Brief Description of Drawings]
[0034]
[Fig. 1] Fig. 1 is a block diagram illustrating an exemplary block configuration of a first embodiment of a communication terminal according to the present invention.

20 [Fig. 2A] Fig. 2A is a network configuration diagram
illustrating an example of a network environment of a mobile
ad-hoc network (MANET) or a delay/disruption tolerant
network (DTN) made up of three communication terminals Al
5 each of which is as illustrated in Fig. 1, where the three
communication terminals Al are interconnected through
wireless communication links LI.
[Fig. 2B] Fig. 2B is a network configuration diagram
illustrating an example of a network environment of a mobile
10 ad-hoc network (MANET) or a delay/disruption tolerant
network (DTN) made up of four communication terminals each of which is as illustrated in Fig. 1, where each of the four communication terminals Al is connected to two neighboring communication terminals Al through wireless communication
15 links LI.
[Fig. 2C] Fig. 2C is a network configuration diagram illustrating an example of a network environment of a mobile ad-hoc network (MANET) or a delay/disruption tolerant network (DTN) made up of seven communication terminals each
20 of which is as illustrated in Fig. 1, where the seven communication terminals Al are connected other communication terminals Al through up to three wireless communication links LI. [Fig. 2D] Fig. 2D is a network configuration diagram
25 illustrating an example of a network environment of a mobile ad-hoc network (MANET) or a delay/disruption tolerant network (DTN) made up of seven communication terminals each of which is as illustrated in Fig. 1, where the seven communication terminals Al are connected to other

21 communication terminal Al through up to four wireless
communication links LI.
[Fig. 3A] Fig. 3A is a table for illustrating an example of kind
of node information managed by the communication terminal
5 illustrated in Fig. 1, where a node ID 11 and a node IP address
12 relating to each communication terminal Al are paired to
form an entry and an expiration date and time 13 is provided for
the entry.
[Fig. 3B] Fig. 3B is a table for illustrating an example of kinds
10 of node information managed by the communication terminal
illustrated in Fig. 1, where a node ID 21 and a routing address 22 relating to each communication terminal Al are paired to form an entry and an expiration date and time 23 is provided for the entry.
15 [Fig. 3C] Fig. 3C is a table for illustrating an example of a kind of node information managed by the communication terminal illustrated in Fig. 1, where a node ID 31 and a node IP address 32 relating to each communication terminal Al and a contents list 33 indicating a list of contents held by the communication
20 terminal Al are associated with each other to form an entry and an expiration date and time 34 is provided for each entry. [Fig. 4A] Fig. 4 is a table for illustrating an example of a kind of routing information managed by the communication terminal illustrated in Fig. 1, where an expiration date and time 43 is
25 provided for the entry.
[Fig. 4B] Fig. 4B is a table for illustrating an example of a kind of routing information managed by the communication terminal illustrated in Fig. 1, where a receipt time 53 or a creation date and time or update time of each entry is provided.

22 [Fig. 4C] Fig. 4C is a table for illustrating an example of a kind
of routing information managed by the communication terminal
illustrated in Fig. 1, where a route score 63 is provided which
is a value indicating the reachability of the destination
5 communication terminal Al of each entry.
[Fig. 5] Fig. 5 is a diagram for illustrating an example of an
operation of the communication terminal illustrated in Fig. 1 as
the first embodiment.
[Fig. 6] Fig. 6 is a flowchart illustrating an example of an
10 operation of the communication terminal illustrated in Fig. 1 as the first embodiment.
[Fig.7] Fig. 7 is a block diagram illustrating an exemplary block configuration of a second embodiment of a communication terminal according to the present invention.
15 [Fig. 8] Fig. 8 is a diagram for illustrating an example of an
operation of the communication terminal illustrated in Fig. 7 as the second embodiment.
[Fig. 9] Fig. 9 is a flowchart illustrating an example of an operation of the communication terminal illustrated in Fig. 7 as
20 the second embodiment.
[Fig. 10] Fig. 10 is a block diagram illustrating an exemplary block configuration of a third embodiment of a communication terminal according to the present invention. [Fig. 11] Fig. 11 is a diagram for illustrating timings of
25 providing node information and routing information held by a communication terminal (node) and periods during which the communication terminal (node) holds the node information and routing information according to an existing technique.

23 [Description of Embodiments]
[0035]
Preferred embodiments of a method for exchanging
information between communication terminals and a
5 communication terminal according to the present invention will
be described with reference to the accompanying drawings.
Note that while a method for exchanging information between
communication terminals and a communication terminal
according to the present invention will be described below, it
10 would be understood that the method for exchanging information between communication terminals may be implemented as a computer-executable program for exchanging information between communication terminals or a program for exchanging information between communication terminals may
15 be recorded on a computer-readable recording medium. [0036] (Features of the Invention)
Prior to describing embodiments of the present invention, an overview of features of the present invention will be
20 described first. A primary feature of the present invention is that both of node information and routing information that are held by a communication terminal (node) are checked and information exchange with another communication terminal (node) and managing information in the communication
25 terminal (node) are performed on the basis of whether or not both of an entry of node information and an entry of routing information that correspond to each other exist. [0037]
Specifically, a primary feature of a communication

24 terminal (node) is that the communication terminal includes
information exchange coordination means which, upon
reception of node information or routing information from
another communication terminal (another node), checks
5 whether or not an entry of routing information or node
information corresponding to the node information or routing
information is missing and, if missing, performs exchange of
the missing routing information or node information, and held
information coordination means which checks node information
10 and routing information held by the communication terminal to determine whether or not an entry of routing information or node information corresponding to the node information or the routing information is missing and, if missing, deletes the node information or the routing information whose corresponding
1 5 entry is missing. [0038]
More specifically, the present invention primarily includes a method for exchanging information between communication terminals and a communication terminal in the
20 following modes. [0039]
A method for exchanging information between communication terminals in a first mode is a method for exchanging node information used for identifying each of a
25 plurality of communication terminals constituting a network among the plurality of communication terminals and routing information indicating a communication route to each of the communication terminals which is a destination between communication terminals. The method is primarily

25 characterized in that when each of the plurality of
communication terminals constituting the network detects
update of the routing information, for example, held by the
communication terminal, the communication terminal
5 references the node information entry corresponding to the
updated routing information entry in the node information held
by the communication terminal and, if a corresponding entry of
the node information does not exists, acquires the node
information entry from another communication terminal.
10 [0040]
A communication terminal in a second mode is a communication terminal which constitutes a network with one or more other communication terminals and exchange node information used for identifying each of the communication
15 terminals and routing information indicating a communication route to each of the communication terminal which is a destination with another communication terminal. Each of the plurality of communication terminals is primarily characterized in that when the communication terminal detects update of the
20 routing information, for example, held by the communication terminal, the communication terminal references the node information entry corresponding to the updated routing information entry in the node information held by the communication terminal and, if a corresponding entry of the
25 node information does not exists, acquires the node information entry from another communication terminal. [0041] (Configuration of First Embodiment)
A first embodiment of the present invention will be

26 described in detail below with reference to Fig. 1. Fig. 1 is a
block diagram illustrating an exemplary block configuration of
the first embodiment of a communication terminal according to
the present invention.
5 [0042]
As illustrated in Fig. 1, a communication terminal Al
includes at least a wireless communication function unit AlOO,
a node information exchange control unit AlOl, a node
information storage unit A102, a routing information exchange
10 control unit A103, a routing information storage unit A104 and information exchange coordination unit A105. [0043]
In the communication terminal Al in Fig. 1, the wireless communication function unit AlOO is a component that performs
15 wireless communication with another communication terminal Alb through a wireless communication link LI; the node information exchange control unit AlOl is a component that controls exchange of node information with another communication terminal Alb; and the node information storage
20 unit A102 is a component that stores node information held by the communication terminal Al. The routing information exchange control unit A103 is a component that controls exchange of routing information with another communication terminal Alb; and the routing information storage unit A104 is
25 a component that stores routing information held by the communication terminal Al. The information exchange coordination unit A105 is a component that monitors the timings of exchanging node information and routing information. The other communication terminal Alb has

27 exactly the same block configuration as the communication
terminal Al in Fig. 1.
[0044]
By using a plurality of communication terminals Al
5 including the components depicted in Fig. 1, wireless
communication is performed by means of the wireless
communication function unit AlOO through a wireless
communication link LI to interconnect the communication
terminals, therefore a mobile ad-hoc network (MANET) or a
10 delay/disruption tolerant network (DTN) can be constructed.
The communication terminals Al in the network may be moving
or stationary.
[0045]
Fig. 2 are network configuration diagrams illustrating
15 examples of network environment of a mobile ad-hoc network (MANET) or a delay/disruption tolerant network (DTN) made up of communication terminals Al each of which is as illustrated in Fig. 1. Fig. 2A illustrates a network configuration made up of three communication terminals Al
20 which are interconnected through wireless communication links LI; Fig. 2B illustrates a network configuration made up of four communication terminals Al each of which is connected with two neighboring communication terminals Al through wireless communication links LI. Figs. 2C and 2D illustrate network
25 configurations each being made up of seven communication
terminals Al; Fig. 2C illustrates a network configuration where there are communication terminals Al each of which is connected with other communication terminals Al through up to three wireless communication links LI and Fig. 2D illustrates a

28 network configuration where there are communication terminals
Al each of which is connected with other communication
terminals Al through up to four wireless communication links
LI.
5 [0046]
The components of the communication terminal Al
illustrated in Fig. 1 will be described below in further detail.
[0047]
(Description of Wireless Communication Function Unit AlOO)
10 The wireless communication function unit AlOO will be
described first. The wireless communication function unit AlOO includes the function of transmitting node information and routing information received from the node information exchange control unit AlOl and the routing information
15 exchange control unit A103 to another communication terminal Alb through a wireless communication link LI. In addition, the wireless communication function unit AlOO includes the function of, when receiving node information and routing information from the other communication terminal Alb
20 through the wireless communication link LI, passing the node information and the routing information to the node information exchange control unit AlOl and the routing information exchange control unit A103, respectively. For example, when the wireless communication function unit AlOO receives node
25 information from another communication terminal Alb, the
wireless communication function unit AlOO passes the received node information to the node information exchange control unit AlOl; when the wireless communication function unit AlOO receives routing information, the wireless communication

29 function unit AlOO passes the received routing information to
the routing information exchange control unit A103.
[0048]
(Description of Node Information Exchange Control Unit AlOl)
5 The node information exchange control unit AlOl will be
described next. The node information exchange control unit
AlOl includes the function of exchanging node information that
the communication terminal Al holds in the node information
storage unit A102 with another communication terminal Alb
10 through the wireless communication function unit AlOO at predetermined regular intervals, the function of exchanging node information with another communication terminal Alb through the wireless communication function unit AlOO in response to an exchange start instruction from the information
15 exchange coordination unit A105, and the function of managing updates of node information that the local communication terminal Al holds in the node information storage unit A102. [0049]
There may be various kinds of node information as
20 illustrated in Figs. 3A to 3C. Figs. 3A to 3C are tables for
illustrating examples of kinds of node information managed by
the communication terminal Al illustrated in Fig. 1.
[0050]
Various kinds of information may be contemplated such
25 as node information NllO illustrated in Fig. 3A in which a node ID 11 and a node IP address 12 relating to each communication terminal Al are paired to form an entry and an expiration date and time 13 is provided for the entry, or node information N120 illustrated in Fig. 3B in which a node ID 21 and a routing

30 address 22 (a special address that serves as a substitute for an
IP address in layered routing or a special address used in
routing) relating to each communication terminal Al are paired
to form an entry and an expiration date and time 23 is provided
5 for the entry, or node information N130 illustrated in Fig. 3C in
which a node ID 31 and a node IP address 32 relating to each
communication terminal Al, and a contents list 33 indicating a
list of contents held by the communication terminal Al are
associated to form an entry and an expiration date and time 34
10 is provided for the entry, for example. [0051]
Furthermore, other node information can be contemplated in which the kinds of node information in Figs. 3A, 3B and 3C are combined. For the sake of simplicity, the node
15 information NllO illustrated in Fig. 3A, i.e. the node
information in which a node ID 11 and a node IP address 12 relating to each communication terminal Al are paired to form an entry and an expiration date and time 13 for the entry of each communication terminal Al is provided will be used in the
20 following description, [0052]
Furthermore, the node information exchange control unit AlOl also manages updates of node information stored in the node information storage unit A102. For the management of
25 updates of the node information, when the node information
exchange control unit AlOl receives node information from the wireless communication function unit AlOO, for example, the node information exchange control unit AlOl reads node information stored in the node information storage unit A102

31 and compares the read node information with the received node
information to determine whether or not the information needs
to be updated.
[0053]
5 If the node information is a new node information entry
that has not been stored in the node information storage unit
A102, the node information exchange control unit AlOl adds
the new node information entry to the existing node
information; if the node information is new information
10 relating to a known node information entry stored in the node information storage unit A102, the node information exchange control unit AlOl overwrites the node information in the node information storage unit A102 with the received new node information entry to update the node information held by the
15 communication terminal Al. In doing so, the node
information exchange control unit AlOl also updates the expiration date and time in accordance with the addition or update of the node information entry. Then the node information exchange control unit AlOl passes the node
20 information added or updated to the node information storage unit A102 for storage. [0054]
Furthermore, the node information exchange control unit AlOl monitors the expiration dates and times of the node
25 information stored in the node information storage unit A102 at predetermined regular intervals. When the node information exchange control unit AlOl detects that an expiration date and time has passed with the passage of time, the node information exchange control unit AlOl performs processing for deleting

32 the node information entry that has the passed expiration date
and time (i.e. an entry whose expiration date and time is earlier
than the current time or an entry for which an invalid-entry flag
is set indicating that the entry is a node information entry that
5 is not used in information exchange) for node information
update management.
[0055]
Furthermore, when a periodic node information
exchanging timing is reached, the node information exchange
10 control unit AlOl retrieves node information managed by the communication terminal Al from the node information storage unit A102 and passes the node information to the wireless communication function unit AlOO to transmit the node information to another communication terminal Alb through the
15 wireless communication link LI. Moreover, when the node information exchange control unit AlOl receives a node information exchange start instruction from the information exchange coordination unit A105, the node information exchange control unit AlOl retrieves node information managed
20 by the communication terminal Al from the node information storage unit A102 and passes the node information to the wireless communication function unit AlOO to transmit the node information to the other communication terminal Alb through the wireless communication link LI.
25 [0056]
(Description of Node Information Storage Unit A102)
The node information storage unit A102 will be described next. The node information storage unit A102 includes the function of storing node information managed by the local

33 communication terminal Al. Specifically, when the node
information storage unit A102 receives node information from
the node information exchange control unit AlOl, the node
information storage unit A102 stores the node information.
5 Furthermore, the node information storage unit A102 also
includes the function of, in response to a node information read
request from the node information exchange control unit AlOl
or the information exchange coordination unit A105, sending
currently stored node information to the requesting node
10 information exchange control unit AlOl or information exchange coordination unit A105. [0057]
(Description of Routing Information Exchange Control Unit A103)
15 The routing information exchange control unit A103 will
be described next. The routing information exchange control unit A103 includes the function of exchanging routing information held by the communication terminal Al in the routing information storage unit A104 with another
20 communication terminal Alb through the wireless
communication function unit AlOO at predetermined regular intervals, the function of exchanging routing information with another communication terminal Alb through the wireless communication function unit AlOO in response to an exchange
25 start instruction from the information exchange coordination unit A105, and the function of managing updates of routing information held by the communication terminal Al in the routing information storage unit A104. [0058]

34 There may be various kinds of routing information as
illustrated in Figs. 4A to 4C. Figs. 4A to 4C are tables for
illustrating examples of kinds of routing information managed
by the communication terminal Al illustrated in Fig. 1.
5 [0059]
Various kinds of information may be contemplated such
as routing information RllO illustrated in Fig. 4A in which a
destination IP address 41 indicating the IP address (Dest. IP
address) of each destination communication terminal Al and a
10 next-hop IP address 42 indicating the IP address (Next hop IP address) of a next-hop communication terminal are paired to form an entry and an expiration date and time 43 is provided for the entry, or routing information R120 illustrated in Fig. 4B in which a destination IP address 51 indicating the IP address of
15 each destination communication terminal Al and a next-hop IP address 52 indicating the IP address of a next-hop communication terminal are paired to form an entry and a receipt time 53 or a creation date and time or update time is provided for the entry, or routing information R130 illustrated
20 in Fig. 4C in which a destination IP address 61 indicating the IP address of each destination communication terminal Al and a next-hop IP address 62 indicating the IP address of a next-hop communication terminal are paired to form an entry and a route score 63 which is a value indicating the reachability of the
25 destination communication terminal Al in the entry is provided, for example. The route score 63 is also used for determining whether or not the entry has expired and, when the route score 63 becomes less than or equal to a predetermined threshold value, the entry is considered to be equivalent to an expired

35 entry and is deleted as invalid routing information.
[0060]
Furthermore, other routing information can be
contemplated in which kinds of node information in Figs. 4A,
5 4B and 4C are combined. For the sake of simplicity, the
routing information RllO illustrated in Fig. 4A, i.e. the routing
information in which a destination IP address 41 and a next-hop
IP address 42 relating to each destination communication
terminal Al are paired to form an entry and an expiration date
10 and time 43 of the entry of each communication terminal Al is provided will be used in the following description. [0061]
Furthermore, the routing information exchange control unit A103 also manages updates of routing information stored
15 in the routing information storage unit A104. For the
management of updates of the routing information, when the routing information exchange control unit A103 receives routing information from the wireless communication function unit AlOO, for example, the routing information exchange
20 control unit A103 reads routing information stored in the
routing information storage unit A104 and compares the read routing information with the received routing information to determine whether or not the information needs to be updated. [0062]
25 If the routing information is a new routing information
entry that has not been stored in the routing information storage unit A104, the routing information exchange control unit A103 adds the new routing information entry to the existing routing information; if the routing information is new

36 information relating to a known routing information entry
stored in the routing information storage unit A104, the routing
information exchange control unit A103 overwrites the routing
information in the routing information storage unit A104 with
5 the received new routing information entry to update the
routing information held by the communication terminal Al.
In doing so, the routing information exchange control unit A103
also updates the expiration date and time in accordance with the
addition or update of the routing information entry. Then the
10 routing information exchange control unit A103 passes the
routing information added or updated to the routing information
storage unit A104 for storage.
[0063]
Furthermore, the routing information exchange control
15 unit A103 monitors the expiration dates and times of the
routing information stored in the routing information storage unit A104 at predetermined regular intervals. When the routing information exchange control unit A103 detects that an expiration date and time has passed with the passage of time,
20 the routing information exchange control unit A103 performs processing for deleting the routing information entry that has the passed expiration date and time (i.e. an entry whose expiration date and time is earlier than the current time, or an entry for which an invalid-entry flag is set indicating that the
25 entry is a routing information entry that is not used in
information exchange, or an entry whose route score becomes less than or equal to a predetermined threshold) for routing information update management. [0064]

37 Furthermore, when a periodic routing information
exchanging timing is reached, the routing information exchange
control unit A103 retrieves routing information managed by the
communication terminal Al from the routing information
5 storage unit A104 and passes the routing information to the
wireless communication function unit AlOO to transmit the
routing information to another communication terminal Alb
through the wireless communication link LI. Moreover, when
the routing information exchange control unit A103 receives a
10 routing information exchange start instruction from the
information exchange coordination unit A105, the routing information exchange control unit A103 retrieves routing information managed by the communication terminal Al from the routing information storage unit A104 and passes the
15 routing information to the wireless communication function unit AlOO to transmit the routing information to the other communication terminal Alb through the wireless communication link LI. [0065]
20 (Description of Routing Information Storage Unit A104) The routing information storage unit A104 will be described next. The routing information storage unit A104 includes the function of storing routing information managed by the communication terminal Al. When the routing
25 information storage unit A104 receives routing information
from the routing information exchange control unit A103, the routing information storage unit A104 stores the routing information. Furthermore, the routing information storage unit A104 also includes the function of, in response to a routing

38 information read request from the routing information exchange
control unit A103 or the information exchange coordination
unit A105, sending currently stored routing information to the
requesting routing information exchange control unit A103 or
5 information exchange coordination unit A105.
[0066]
(Description of Information Exchange Coordination Unit A105)
The information exchange coordination unit A105 will be
described next. The information exchange coordination unit
10 A105 includes the function of monitoring node information stored in the node information storage unit A102 and routing information stored in the routing information storage unit A104 at predetermined regular intervals to detect whether or not addition of new information to or update of both of the node
15 information and routing information has occurred as a result of information exchange with another communication terminal Alb. When the information exchange coordination unit A105 detects addition to or update of only one of the node information and the routing information, the information
20 exchange coordination unit A105 sends an exchange start
instruction to the node information exchange control unit AlOl or the routing information exchange control unit A103 to instruct to start exchange of the other information (node information or routing information) to which addition of new
25 information or update has not occurred. [0067]
For example, the information exchange coordination unit A105 performs an operation illustrated in the diagram of Fig. 5. Fig. 5 is a diagram for illustrating an example of an operation

39 of the communication terminal Al illustrated in Fig. 1 as the
first embodiment. The diagram of Fig. 5 illustrates an
example of an operation in which the communication terminal
Ala (node 1) receives a routing information entry RllOy
5 relating to another communication terminal Y from another,
neighboring communication terminal Alb (node 2) connected to
the communication terminal Ala and, when the routing
information entry RllOy relating to the communication
terminal Y is updated but a node information entry NllOy
10 corresponding to the routing information entry RllOy relating to the communication terminal Y does not exist, the communication terminal Ala starts exchanging the node information entry NllOy relating to the communication terminal Y with the connected neighboring communication
15 terminal Alb (node 2). [0068]
In the diagram of Fig. 5, the communication terminal Ala (node 1) holds node information NllO and routing information RllO in the node information storage unit A102 and the routing
20 information storage unit A104, respectively. A situation will be described below in which the routing information RllO is updated first. [0069]
As illustrated in the diagram of Fig. 5, when the
25 communication terminal Ala (node 1) receives a routing
information message including a routing information entry RllOy relating to a new, another communication terminal Y from another communication terminal Alb (sequence Seql), the routing information exchange control unit A103 updates the

40 routing information RllO stored in the routing information
storage unit A104 to add the routing information entry RllOy
relating to the new communication terminal Y (sequence Seq2).
[0070]
5 On the other hand, the information exchange coordination
unit A105 monitors the routing information RllO stored in the
routing information storage unit A104 at predetermined regular
intervals as stated above. When the information exchange
coordination unit A105 detects update of the routing
10 information entry RllOy relating to the communication terminal Y (sequence Seq3), the information exchange coordination unit A105 performs an operation for determining whether or not a node information entry NllOy that corresponds to the routing information entry RllOy relating to the
15 communication terminal Y exists in the node information storage unit A102 (sequence Seq4). [0071]
When the node information entry NllOy that corresponds to the updated routing information entry RllOy relating to the
20 communication terminal Y does not exist in the node
information storage unit A102, the information exchange coordination unit A105 sends an exchange start instruction for the node information entry NllOy relating to the communication terminal Y to the node information exchange
25 control unit AlOl to cause the node information exchange
control unit AlOl to start an operation for exchanging the node information entry NllOy relating to the communication terminal Y with the other communication terminal Alb (sequence Seq5).

41 [0072]
Note that it is assumed in the diagram of Fig. 5 that the
communication terminal Ala (node 1) is located within a range
in which the communication terminal Ala (node 1) can
5 communication with the neighboring other communication
terminal Alb (node 2) and is connected with the neighboring
communication terminal Alb (node 2) through a wireless
communication link LI. The communication terminal Ala
(node 1) has received a new routing information entry RllOy
10 for routing to the communication terminal Y from the connected other communication terminal Alb (node 2) as indicated by sequence Seql. [0073]
When the information exchange coordination unit A105
15 detects that addition or update of the routing information entry RllOy for routing to the other communication terminal Y has occurred in the routing information RllO held in the routing information storage unit A104 of the communication terminal Ala (node 1) as indicated by sequence Seq3, the information
20 exchange coordination unit A105 performs an operation for determining whether or not a node information entry NllOy relating to the other communication terminal Y that corresponds to for which the routing information entry RllOy has been newly added or updated is recorded in the node
25 information storage unit A102, as indicated by sequence Seq4. [0074]
The determination as to whether or not a node information entry NllOy that corresponds to the routing information entry RllOy relating to the other communication

42 terminal Y is recorded in the node information storage unit
A102 may be made by comparing the destination IP address in
the routing information entry RllOy recorded in the destination
IP address 41 in the routing information storage unit A104 with
5 each of the node IP addresses recorded in the node IP address
12 in the node information storage unit A102. In other words,
since common items (IP addresses, i.e. node IP addresses 12
and destination IP addresses 41 in the first embodiment) are
stored in the node information and the routing information so
10 that mutually corresponding entries of the both kinds of information can be cross-referenced, the common items of information may be used to identify corresponding entries between the node information and the routing information. [0075]
15 Ifa node information entry NllOy that corresponds to the
routing information entry RllOy relating to the communication terminal Y is not recorded in the node information storage unit A102, the node information entry NllOy relating to the other communication terminal Y needs to be acquired from the
20 neighboring communication terminal Alb. Therefore the information exchange coordination unit A105 sends a node information exchange start instruction to the node information exchange control unit AlOl. The node information exchange control unit AlOl receives the node information exchange start
25 instruction and performs an operation for exchanging node
information with the communication terminal Alb through the wireless communication function unit AlOO in order to acquire the node information entry NlOOy relating to the other communication terminal Y as indicated by sequence Seq5.

43 [0076]
If the node information entry NllOy that corresponds to
the routing information entry RllOy relating to the
communication terminal Y is recorded in the node information
5 storage unit A102 but a predetermined period of time has
elapsed since the creation of the node information entry NllOy
and the expiration date and time has passed, the information
exchange coordination unit A105 determines that the node
information entry NllOy has been expired, deletes the node
10 information entry NllOy and may send a node information exchange start instruction to the node information exchange control unit AlOl in order to acquire the node information entry NllOy relating to the communication terminal Y anew from the communication terminal Alb.
15 [0077]
On the other hand, if the node information entry NllOy that corresponds to the routing information entry RllOy relating to the communication terminal Y is recorded in the node information storage unit A102 and the predetermined
20 period of time has not elapsed since the creation of the node information entry NllOy, the information exchange coordination unit A105 determines that the operation for exchanging the routing information entry RllOy relating to the other communication terminal Y does not need to be performed
25 and therefore does not perform the subsequent process. [0078]
While the operation that starts in response to receipt of new routing information has been described above, the same process may be performed in response to receipt of new node

44 information, in which case the term routing information and the
term node information in the foregoing description are
interchanged.
[0079]
5 Thus, when only one of a pair of a rouging information
entry RllOy and a node information entry NllOy relating to
another communication terminal Y is added or updated, the
communication terminal Ala (node 1) can add or update both of
the routing information entry RlOOy and the node information
10 entry NllOy relating to the other communication terminal Y at substantially the same time, instead of adding or updating only one of the routing information entry RllOy and the node information entry NllOy relating to the other communication terminal Y, by performing the operation illustrated in Fig. 5.
15 In this way, the communication terminal Ala (node 1) is allowed to provide both of node information and routing information relating to a particular communication terminal together to another communication terminal (for example the communication terminal Alb (node 2)) during information
20 exchange with the other communication terminal. [0080]
Furthermore, addition of new information to or update of node information or routing information may be detected at the information exchange coordination unit A105 by performing the
25 following process. When the information exchange
coordination unit A105 references the node information storage unit A102 or the routing information storage unit A104 at predetermined regular intervals, the information exchange coordination unit A105 may read and store node information or

45 routing information relating to each communication terminal.
At each regular reference to node information or the routing
information, the information exchange coordination unit A105
may check whether there is a difference between the node
5 information or the routing information and the previously
stored node information or routing information relating to each
communication terminal to determine whether or not node
information or routing information relating to each
communication terminal has been added or updated.
10 [0081]
Alternatively, when the node information exchange control unit AlOl or the routing information exchange control unit A103 detects addition of new information to or update of node information or routing information, the node information
15 exchange control unit AlOl or the routing information exchange control unit A103 may notify the information exchange coordination unit A105 of the addition or the update. [0082]
Furthermore, the timing of performing detection of
20 addition of new information to or update of node information or routing information at the information exchange coordination unit A105 may be as follows: when the node information exchange control unit AlOl or the routing information exchange control unit A103 receives node information or routing
25 information from the wireless communication function unit
AlOO, the node information exchange control unit AlOl or the routing information exchange control unit A103 may send a notification of the receipt to the information exchange coordination unit A105 and, in response to the notification, the

46 information exchange coordination unit A105 may check the
information in the node information storage unit A102 or the
routing information storage unit A104 for addition or update,
instead of checking at predetermined regular intervals. It is
5 assumed in the following description that the information
exchange coordination unit A105 monitors for addition or
update of node information and routing information at
predetermined regular intervals.
[0083]
10 (Description of Operation of First Embodiment)
An example of an operation of the communication terminal Al illustrated in Fig. 1 as the first embodiment will be described below in further detail with reference to the diagram of Fig. 5 and the flowchart of Fig. 6. The diagram of Fig. 5
15 illustrates an example of an operation for starting exchange of a node information entry NllOy relating to another communication terminal Y between a communication terminal Ala (node 1) and another communication terminal Alb (node 2) as described above.
20 [0084]
Fig. 6 is a flowchart illustrating an example of an operation of the communication terminal Al illustrated in Fig. 1 as the first embodiment. Fig. 6 illustrates an example of a process flow in which the information exchange coordination
25 unit A105 in the communication terminal Ala (node 1) in the diagram of Fig. 5 monitors for addition of new information to or update or expiration of node information or routing information at predetermined regular intervals and starts the operation for exchanging required node information or routing

47 information with another communication terminal (the
communication terminal Alb in Fig. 5) connected to the
communication terminal Ala as needed. In other words, Fig. 6
illustrates an example of an operation that enables both of node
5 information and routing information, rather than only one of
the node information and the routing information, to be passed
at substantially the same time.
[0085]
Note that the process in the flowchart of Fig. 6 illustrates
10 the operation that is performed at predetermined regular
intervals as described above. While the operation illustrated in Figs. 5 and 6 is actually performed at each of the communication terminals that constitute a network as illustrated in any of Figs. 2A to 2D, the following description
15 will focus only on a communication terminal Ala (node 1) and another communication terminal Alb (node 2) illustrated in Fig. 5 among the communication terminals constituting the network, and be given on a case where an operation for exchanging node information and routing information between the two
20 communication terminals is performed for simplicity. [0086]
First, it is assumed that the communication terminal Ala (node 1) and the other communication terminal Alb (node 2) illustrated in Fig. 5 are within a range in which the two
25 communication terminals can communicate with each other and are interconnected through a wireless communication link LI, as described above. While node information may be received first or routing information may be received first in information exchange between the communication terminal Ala

48 (node 1) and the other communication terminal Alb (node 2),
only a pattern in which routing information is received first
will be described below in detail since the same operation is
performed for exchange of different kinds of information as
5 noted previously.
[0087]
As described previously with respect to sequence Seql in
Fig. 5, the communication terminal Alb transmits routing
information that the communication terminal Alb currently
10 holds to the communication terminal Ala as periodic
transmission of routing information. The communication terminal Ala receives the routing information from the communication terminal Alb through the wireless communication function unit AlOO and passes the received
15 routing information to the routing information exchange control unit A 1 03 . [0088]
The routing information exchange control unit A103 receives the received routing information (routing information
20 including a routing information entry RllOy relating to the
communication terminal Y (node Y) in the example in Fig. 5) from the wireless communication function unit AlOO, generates a new entry with a destination IP address 41 (Dest. IP address) of '192.168.0.1', a next pop IP address 42 (Next-hop IP address)
25 of '192.168.0.5', and an expiration date and time 43 of
'2012/08/29 13:00:00' in order to adds the routing information entry RllOy relating to the new communication terminal Y (node Y), for example, in the received routing information, updates the routing information with the entry RllOy, and

49 passes the updated routing information to the routing
information storage unit A104. The routing information
storage unit A104 receives the routing information from the
routing information exchange control unit A103 and stores the
5 routing information as the latest routing information at the
local communication terminal Ala as described with respect to
sequence Seq2 in Fig. 5.
[0089]
On the other hand, the communication terminal Ala is
10 periodically monitoring node information in the node
information storage unit A102 and routing information in the routing information storage unit A104 of the local communication terminal Ala for an update by using the information exchange coordination unit A105 all the while.
15 Specifically, the information exchange coordination unit A105 reads routing information stored in the routing information storage unit A104 at predetermined regular intervals and uses the read routing information and the routing information stored by the information exchange coordination unit A105 at the
20 previous checking to determine whether or not the routing information has been updated, as described above. [0090]
When the information exchange coordination unit A105 detects update of the routing information entry RllOy relating
25 to the communication terminal Y (node Y) as a result of the
checking as described previously with respect to sequence Seq3 in Fig. 5, the information exchange coordination unit A105 activates a determination process for exchange of node information and routing information with other communication

50 terminals illustrated in the flowchart of Fig. 6.
[0091]
When the process in the flowchart of Fig. 6 is activated,
first the information exchange coordination unit A105 reads
5 node information held by the local communication terminal Ala
from the node information storage unit A102 in order to check
information corresponding to the information found to be
updated, i.e. a node information entry NllOy relating to the
communication terminal Y (node Y) that corresponds to the
10 routing information entry RllOy relating to the communication terminal Y (node Y) in this embodiment (step SlOO), and uses the updated routing information entry RllOy relating to the communication terminal Y (node Y) to check whether or not a node information entry NllOy corresponding to the routing
15 information entry RllOy exists in the node information held by the communication terminal Ala (step SlOl). [0092]
In this embodiment, checking is performed to determine whether or not a node information entry NllOy in which the
20 same node IP address as the IP address of the destination communication terminal Y, '192.168.0.1', written in the destination IP address 41 (Dest. IP address) in the updated routing information entry RllOy in Fig. 5 is written in the node IP address 11 in Fig. 5 exists in the node information storage
25 unit A102 as described above. [0093]
As described with reference to Fig. 5, in this embodiment, because a node information entry NllOy with the same node IP address as the IP address of the destination communication

51 terminal Y, '192.168.0.1', in the updated routing information
entry RllOy relating to the communication terminal Y (node Y)
does not exist in the node information storage unit A102 (No at
step SlOl), the information exchange coordination unit A105
5 determines that the updated routing information entry RllOy
relating to the communication terminal Y (node Y) is a newly
added piece of information and the node information entry
NllOy corresponding to the routing information entry RllOy
relating to the communication terminal Y (node Y) needs to be
10 newly acquired. The process therefore proceeds to step S103, where an operation for exchanging the corresponding information with a neighboring other communication terminal Alb connected to the communication terminal Ala is performed to acquire the corresponding information (step S103).
15 [0094]
In this embodiment, the corresponding information exchanged at step S103 is the node information entry NllOy relating to the communication terminal Y (node Y) as described above and the information exchange coordination unit A105
20 sends an exchange start instruction to the node information exchange control unit AlOl to instruct the node information exchange control unit AlOl to perform an operation to exchange node information including the node information entry NllOy relating to the communication terminal Y (node Y) with the
25 other communication terminal Alb. As a result, the node information entry NllOy relating to the communication terminalY(nodeY)canbereceivedfromtheother communication terminal Alb and the node information can be updated with the received node information entry NllOy

52 relating to the communication terminal Y (node Y) at the node
information exchange control unit AlOl, the updated node
information can be passed to the node information storage unit
A102 and can be stored in the node information storage unit
5 A102 (step S103). Thus, the communication terminal Ala
(node 1) can update not only the routing information entry
RllOy relating to the communication terminal Y (node Y) but
also the corresponding node information entry NllOy relating
to the communication terminal Y (node Y) at substantially the
1 0 same time. [0095]
On the other hand, if the node information entry Nl lOy
with the same node IP address as the IP address of the
destination communication terminal Y, '192.168.0.1', in the '
15 updated routing information entry RllOy relating to the communication terminal Y (node Y) exists in the node information storage unit A102 at step SlOl (Yes at step SlOl), the information exchange coordination unit A105 determines that the updated routing information entry RllOy relating to the
20 communication terminal Y (node Y) has not been newly added but already held routing information has been updated. Accordingly, the process proceeds to step S102 in order to check whether or not the node information entry NllOy relating to the communication terminal Y (node Y) that is stored in the
25 node information storage unit A102 correspondingly to the routing information entry RllOy has become old and can no longer be used. [0096]
At step S102, the information exchange coordination unit

53 A105 references the node information entry NllOy relating to
the communication terminal Y (node Y) that corresponds to the
updated routing information entry RllOy relating to the
communication terminal Y (node Y) to determine whether or not
5 the date written in the expiration date and time 13 in Fig. 5 is
earlier than the current date, indicating that the node
information entry NllOy has expired (step S102).
[0097]
If the information exchange coordination unit A105
10 determines that the information is expired old information (Yes at step S102), the information exchange coordination unit A105 deletes the node information entry NllOy relating to the communication terminal Y (node Y) from the node information storage unite A102, then proceeds to step S103 and instructs the
15 node information exchange control unit AlOl to start an
operation for exchanging information corresponding to the updated routing information entry RllOy relating to the communication terminal Y (node Y), i.e. the node information including the node information entry NllOy relating to the
20 communication terminal Y (node Y). Accordingly, the node
information exchange control unit AlOl performs the operation for exchanging the node information including the node information entry NllOy relating to the communication terminal Y (node Y) with the other communication terminal Alb
25 to acquire the node information entry NllOy relating to the communication terminal Y (node Y) (step S103). [0098]
On the other hand, at step S102, if the information exchange coordination unit A105 determines that the node

54 information in tlie node information entry NllOy relating to the
communication terminal Y (node Y) that is stored in the node
information storage unit A102 has not expired and is not
obsolete (No at step S102), then the information exchange
5 coordination unit A105 ends the process without performing
further processing.
[0099]
As described above in detail, the information exchange
coordination unit A105 performs the process from step SlOO
10 through step S103 in Fig. 6 to enable the communication terminal Ala to be placed in a "state where both of node information and routing information are managed in association with each other or a state where both of the two kinds of information are held". In other words, when the
15 communication terminal Ala exchanges routing information relating to a particular communication terminal, for example the communication terminal Y (node Y), with another communication terminal, for example the communication terminal Alb, connected to the communication terminal Ala,
20 the communication terminal Ala can exchange not only the
routing information relating to the particular communication terminal, for example the communication terminal Y (node Y), but also the corresponding node information, i.e. both of the routing information and the node information relating to the
25 particular communication terminal, for example the
communication terminal Y (node Y), at substantially the same
time.
[0100]
Note that while a case where routing information is

55 received first has been described in the description of the
diagram of Fig. 5 and the flowchart of Fig. 6 for the sake of
simplicity, the same process is performed when node
information is received first, except that the term routing
5 information and the term node information in the foregoing
description are interchanged, as noted above. Furthermore,
when corresponding information is checked, expiration of a
node information entry is considered to be equivalent to
absence of the entry as noted above. In the case of a routing
10 information entries, not only a routing information entry that has expired but also a routing information entry whose route score is less than or equal to a predetermined threshold value is considered to be equivalent to a missing entry, as noted above. [0101]
15 (Configuration of Second Embodiment)
A second embodiment of the present invention will be described next in detail with reference to the block diagram of Fig. 7. Fig. 7 is a block diagram illustrating an exemplary block configuration of the second embodiment of a
20 communication terminal according to the present invention. [0102]
The communication terminal Al in Fig. 1 described as the first embodiment exchanges node information or routing information on the basis of whether or not both of an entry of
25 node information and an entry of routing information that correspond to each other exist to acquire both of the node information and the routing information at substantially the same time and updates the information in the node information storage unit A102 and the routing information storage unit

56 A104. The communication terminal Al of the second
embodiment illustrated in Fig. 7, on the other hand, determines
whether or not an entry of node information or routing
information is to be held by the communication terminal Al on
5 the basis of whether or not there is a corresponding entry of the
other kind of information out of the node information and the
routing information held by the communication terminal Al and,
if the communication terminal Al determines that the
information entry is not to be held by the communication
10 terminal Al, the communication terminal deletes the relevant information stored in the node information storage unit A102 or the routing information storage unit A104. [0103]
For that purpose, the communication terminal Al of the
15 second embodiment illustrated in Fig. 7 newly includes a held information coordination unit A106 instead of the information exchange coordination unit A105 of the communication terminal Al of the first embodiment illustrated in Fig. 1. The other components are the same as those of the communication
20 terminal Al of the first embodiment illustrated in Fig. 1. Therefore only the function of the new, held information coordination unit A106 will be described below and the repeated description of the other components will be omitted. [0104]
25 (Description of Held Information Coordination Unit A106)
The held information coordination unit A106 includes the function of checking routing information entries that correspond to node information entries stored in a node information storage unit A102 and node information entries that

57 correspond to routing information entries stored in a routing
information storage unit A104 at predetermined regular
intervals and, if an entry of one of the node information and the
routing information that corresponds to an entry of the other
5 kind of information does not exist, or if a corresponding
information entry exists but the entry has expired, deleting the
information entry.
[0105]
For example, when the held information coordination unit
10 A106 periodically monitors routing information, the held
information coordination unit A106 determines whether or not a node information entry held by the communication terminal Al that corresponds to a routing information entry held by the communication terminal Al in the routing information storage
15 unit A104 exists in the node information storage unit A102, or whether or not such an existing corresponding entry has expired. If the corresponding node information entry does not exists in the node information storage unit A102 or if the corresponding node information exists in the node information storage unit
20 A102 but has expired, the held information coordination unit A106 determines that the routing information entry is unnecessary and deletes the routing information entry from the routing information storage unit A104. [0106]
25 Similarly, when the held information coordination unit
A106 periodically monitors the node information, the held information coordination unit A106 determines whether or not a routing information entry held by the communication terminal Al that corresponds to a node information entry held by the

58 communication terminal Al in the node information storage
unit A102 exists in the routing information storage unit A104,
or whether or not such an existing corresponding entry has
expired. If the corresponding routing information entry does
5 not exists in the routing information storage unit A104 or if the
corresponding routing information exists in the routing
information storage unit A104 but has expired, the held
information coordination unit A106 determines that the node
information entry is unnecessary and deletes the node
10 information entry from the node information storage unit A102. [0107]
In this way, a routing information entry corresponding to a node information entry or a node information entry corresponding to a routing information entry is checked to
15 manage information to be locally held by the communication terminal A 1 . [0108]
Specifically, in addition.to checking whether a corresponding information entry exists as described above,
20 checking of the predetermined expiration dates and times of information entries is performed and an information entry whose expiration date and time has passed may be determined to be obsolete information that can no longer be used at the current time and may be deleted like an information entry that
25 does not has a corresponding information entry. For example, in the case of node information entries, when the predetermined expiration date and time of a node information has passed, the node information entry may be determined to be invalid information that cannot be used and may be removed from the

59 node information storage unit A102. In the case of routing
information entries, wlien the route score value of a routing
information entry becomes less than or equal to a predetermined
threshold value, the routing information entry may be treated
5 like an expired entry, may be considered to be invalid
information that cannot be used and may be deleted from the
routing information storage unit A104.
[0109]
Furthermore, instead of or in addition to checking node
10 information in the node information storage unit A102 and routing information in the routing information storage unit A104 of the communication terminal Al at predetermined regular intervals, the held information coordination unit A106 may check the node information and the routing information
15 held by the local communication terminal Al at any of various set timings. [0110]
For example, before a node information exchange control unit AlOl or a routing information exchange control unit A103
20 exchanges node information or routing information with a neighboring other communication terminal Alb through a wireless communication function unit AlOO, the node information exchange control unit AlOl or the routing information exchange control unit A103 may send a notification
25 of the exchange to the held information coordination unit A106. In response to the notification, the held information coordination unit A106 may check node information in the node information storage unit A102 or routing information in the routing information storage unit A104 of the local

60 communication terminal Al. In this case, before performing
the operation for exchanging node information or routing
information, unnecessary information entries can be deleted
and therefore the amount of information required to be
5 exchanged with the other communication terminal Alb can be
reduced.
[0111]
Alternatively, when the node information exchange
control unit AlOl or the routing information exchange control
10 unit A103 receives a notification of checking node information or routing information from a neighboring other communication terminal Alb through the wireless communication function unit AlOO, the node information exchange control unit AlOl or the routing information exchange control unit A103 may send the
15 received notification of checking to the held information
coordination unit A106, and in response to the notification, the held information coordination unit A106 may check node information in the node information storage unit A102 or routing information in the routing information storage unit
20 A104 of the local communication terminal Al. [0112]
In this case, when the held information coordination unit A106 detects a routing information entry or a node information entry that does not have a corresponding node information entry
25 or a corresponding routing information entry, or detects a
routing information entry or a node information entry that has a corresponding node information entry or routing information entry but has expired, the held information coordination unit A160 may send information about the detected routing

61 information entry or node information entry as information
indicating a candidate information entry to be deleted back to
the neighboring communication terminal Alb that has sent the
notification of checking. The neighboring communication
5 terminal Alb which has received the sent back information can
reference the information in determining whether or not there is
an information entry to be deleted as will be described later.
[0113]
Furthermore, when the held information coordination unit
10 A106 determines whether or not information is to be held in the local communication terminal Al, the held information coordination unit A106 may also reference information at another communication terminal Alb located near the local communication terminal Al instead of referencing only the
15 information at the local communication terminal Al as described above. [0114]
For example, the held information coordination unit A106 may perform an operation illustrated in the diagram of Fig. 8.
20 Fig. 8 is a diagram for illustrating an example of an operation of the communication terminal Al illustrated in Fig. 7 as the second embodiment. The diagram of Fig. 8 illustrates both of an example of an operation in which the held information coordination unit A106 of the communication terminal Ala
25 (node 1) uses information at the local communication terminal Ala (node 1) alone to determine which information is to be held and which formation is to be deleted out of the node information and the routing information held at the communication terminal Ala (node 1) and an example of an

62 operation in which the held information coordination unit A106
also references information at a neighboring other
communication terminal Alb (node 2) connected to the
communication terminal Al to determine information to be held
5 and information to be deleted.
[01 15]
In the diagram of Fig. 8, the communication terminal Ala
(node 1) holds node information NllO and routing information
RllO in the node information storage unit A102 and the routing
10 information storage unit A104, respectively. In the example described below, the routing information RllO is checked first. [0116]
As illustrated in the diagram of Fig. 8, if information to be held is determined using only the information in the local
15 communication terminal Ala (node 1), the held information coordination unit A106 of the communication terminal Ala (node 1) first reads routing the information RllO held at the local communication terminal Ala (node 1) from the routing information storage unit A104. The held information
20 coordination unit A106 then determines whether or not node information entries exist in the node information NllO stored in the node information storage unit A102 that correspond to routing information entries in the routing information RllO, or whether or not corresponding node information entries in the
25 node information NllO have expired (sequence SeqlO). [0117]
The determination as to whether or not an entry of a node information NllO that corresponds to each entry of a routing information RllO relating to each communication terminal

63 exists in the node information storage unit A102 may be made
by comparing the destination IP address in the entry of the
routing information RllO recorded in the destination IP address
41 (Dest. IP address) in the routing information storage unit
5 A104 with each of the node IP addresses of each entry of the
node information NllO recorded in the node IP address 12 in
the node information storage unit A102, as described in the
first embodiment.
[01 18]
10 The diagram of figure 8 illustrates a situation in which
node information entries that have the same node IP addresses as the destination IP addresses of routing information entries in the routing information RllO relating to the communication terminals exist in the node information NllO and node
15 information entries that correspond to the routing information entries relating to the communication terminals exist in the node information storage unit A102. However, the node information entry NllOy relating to a communication terminal Y (node Y) has expired as 'Time Out' is written in the
20 expiration date and time 13 of the node information entry NllOy (with a node IP address of '192.168.0.3') that corresponds to the routing information entry RllOy relating to the communication terminal Y (node Y) (with a destination IP address of '192.168.0.3').
25 [0119]
Accordingly, the held information coordination unit A106 determines that the node information entry NllOy relating to the communication terminal Y (node Y) is equivalent to information that does not exist and that the routing information

64 entry RllOy and the node information entry NllOy relating to
the communication terminal Y (node Y) is information to be
deleted, and immediately deletes the routing information entry
RllOy and the node information entry NllOy. Note that since
5 the routing information is checked at this point, the node
information entry NllOy that has expired may be deleted when
checking the node information rather than deleting at this
point.
[0120]
10 Alternatively, the held information coordination unit
A106 may check the expiration date and time written in the expiration date and time 13 of the node information entry NllOy corresponding to the routing information entry RllOy relating to the communication terminal Y (node Y) to be
15 checked. If the node information entry NllOy has expired, the held information coordination unit A160 may simply overwrite the expiration date and time 13 with 'Time Out' as illustrated in Fig. 8 and may leave the deletion of the node information entry NllOy from the node information storage unit A102 to the node
20 information exchange control unit AlOl. Similarly, the held information coordination unit A106 may simply overwrite the expiration date and time 43 of the routing information entry RllOy relating to the communication terminal Y (node Y) to be checked with 'Time Out' and may leave the deletion of the
25 routing information entry RllOy from the routing information storage unit A104 to the routing information exchange control unit A103. [0121]
Similarly, the held information coordination unit A106 of

65 the communication terminal Ala (node 1) determines whether or
not routing information entries corresponding to the node
information entries exist on the basis of the node information
NllO held by the communication terminal Ala (node 1), or
5 whether or not the corresponding routing information entries
have expired (sequence SeqlO). If a routing information entry
that corresponds to a node information entry does not exist or if
the expiration date and time of a routing information entry that
is written in the expiration date and time 43 has passed, the
10 held information coordination unit A106 determines that the node information entry or the node information entry and its corresponding routing information entry are information to be deleted. [0122]
15 In this way, if only the information at the local
communication terminal Ala (node 1) is used to determine information to be held, the held information coordination unit A106 references node information NllO stored in the node information storage unit A102 of the communication terminal
20 Ala (node 1) and the routing information RllO stored in the
routing information storage unit A104 to check whether or not there are node information entries that correspond to the entries of the routing information RllO and routing information entries that correspond to the entries of the node information
25 NllO, and whether or not there are entries that have expired, thereby checking whether information is to be deleted or to be held. If an information entry that has not a corresponding information entry or that has expired is detected, the held information coordination unit A106 determines that the

66 information entry is invalid information that does not need to
be held and immediately deletes the information entry as
information to be deleted or leave the deletion of the
information entry to the node information exchange control unit
5 AlOl or the routing information exchange control unit A103,
thereby preventing the information entry from being uselessly
held.
[0123]
Note that when the held information coordination unit
10 A106 detects a predetermined expiration date and time of an
information entry has passed, the held information coordination unit A106 may set an 'invalid-entry flag' indicating that the information entry is invalid information in the expiration date and time 13 or the expiration date and time 43 instead of
15 overwriting with 'Time Out' as illustrated in Fig. 8, to leave the deletion of the information entry to the node information exchange control unit AlOl or the routing information exchange control unit A103. When 'Time Out' or the 'invalid-entry flag' is set in the expiration date and time 13 or the expiration date
20 and time 43, 'Time Out' or the 'invalid-entry flag' may be
forcibly set in the expiration date and time 43 or the expiration date and time 13 of an information entry that corresponds to the information entry, as described above. [0124]
25 If information at a neighboring other communication
terminal Alb (node 2) is used in addition to the information at the local communication terminal Ala (node 1) to determine information to be held at the local communication terminal Ala (node 1), the held information coordination unit A106 of the

67 local communication terminal Ala (node 1) first performs an
operation for exchanging a notification of checking of routing
information with the held information coordination unit A106
of the neighboring communication terminal Alb (node 2)
5 through the routing information exchange control unit A103 and
the wireless communication function unit AlOO as illustrated in
the diagram of Fig. 8 (sequence Seqll).
[0125]
The held information coordination unit A106 of the
10 communication terminal Ala (node 1) receives the notification of routing information checking from the correspondent communication terminal Alb (node 2) and performs the checking operation described above as sequence SeqlO, extracts routing information entries that do not have corresponding node
15 information entries or routing information entries that have
expired from the routing information entries of communication terminals at the local communication terminal Ala (node 1) as candidate information to be deleted, places the routing information entries on a list of candidates to be deleted (at the
20 local communication terminal), stores the list, and sends the list of candidates to be deleted (at the local communication terminal) back to the correspondent communication terminal Alb (node 2) that has sent the checking notification as a list of candidates to be deleted (at the correspondent communication
25 terminal) (sequence Seql2). [0126]
On the other hand, the held information coordination unit A106 of the correspondent communication terminal Alb (node 2), which has received the routing information checking

68 notification from the communication terminal Ala (node 1),
performs the same operation to extract candidate information to
be deleted at the communication terminal Alb (node 2), places
the candidate information on a list of candidates to be deleted
5 (at the local communication terminal), stores the list, and sends
the list of candidates to be deleted (at the local communication
terminal) to the communication terminal Ala (node 1) that has
sent the checking notification as a list of candidates to be
deleted (at the correspondent communication terminal)
10 (sequence Seql2). [0127]
The lists of candidates to be deleted that are exchanged between the communication terminal Ala (node 1) and the correspondent communication terminal Alb (node 2) need only
15 to list common information for cross-referencing node
information and routing information, i.e. information that identifies candidate information entries to be deleted and need to contain at least the IP addresses indicating the candidate communication terminals (nodes) to be deleted (i.e. node IP
20 addresses in the node information and destination IP addresses in the routing information), as described above. In the example in Fig. 8, the node IP address '191.168.0.3' ofthe communication terminal Y (node Y) for which 'Time Out' is set in the expiration date and time 13 in the node information needs
25 only to be listed as candidate routing information to be deleted (since the node information entry has been expired, the node information entry itself is candidate node information to be deleted, of course). [0128]

69 The held information coordination unit A106 of the
communication terminal Ala (node 1) receives the list of
candidates to be deleted from the communication terminal Alb
(node 2) and uses the combination of the received list of
5 candidates to be deleted (at the correspondent communication
terminal) and the list of candidates to be deleted (at the local
communication terminal) created and stored at the local
communication terminal (node 1) through the checking
operation described above as sequence SeqlO to determine
10 invalid information that does not need to be held at the communication terminal Ala (node 1). [0129]
While only one other communication terminal Alb (node 2) is given as neighboring the communication terminal Ala
15 (node 1) in Fig. 8, the present invention is not limited to this; a plurality of other communication terminals may be within an area in which the communication terminals can communicate with each other through wireless links. In that case, the local communication terminal Ala (node 1) sends a list of candidates
20 to be deleted (at the local communication terminal) to each of the plurality of other communication terminals and receives lists of candidates to be deleted (at the correspondent communication terminals) from the plurality of other communication terminals.
25 [0130]
Determination as to whether or not information is invalid information that does not need to be held may be made using various methods. For example, a method may be used in which if the IP address of the same communication terminal (for

70 example the communication terminal Y (node Y) depicted in Fig.
8) is placed on all of the list of candidates to be deleted (at the
local communication terminal) and the lists of candidates to be
deleted (at the correspondent communication terminals) (i.e. if
5 the IP address is in the product set of the list of candidates to
be deleted at local communication terminal Ala and the lists of
candidates to be deleted at all of the neighboring other
communication terminals), it is determined that the node
information and the routing information relating to the
10 communication terminal identified by the IP address are invalid pieces of information that do not need to be held. [0131]
Alternatively, a method may be used in which if the IP address of a communication terminal (for example the
15 communication terminal Y (node Y) depicted in Fig. 8) is
placed on at least one of the list of candidates to be deleted (at the local communication terminal) and the lists of candidates to be deleted (at the correspondent communication terminals) (i.e. the IP address is in the union of the list of candidates to be
20 deleted at the local communication terminal Ala and lists of candidates to be deleted at all of the neighboring other communication terminals), it is determined that the node information and the routing information relating to the communication terminal identified by the IP address are invalid
25 pieces of information that do not need to be held. [0132]
Note that instead of using the lists of candidates to be deleted of all of the other communication terminals neighboring the local communication terminal Ala (the lists at the

71 correspondent communication terminals), weights may be
assigned to all of the other communication terminals using the
intensity of electrical field between the local communication
terminal Ala and each of the other communication terminals,
5 communication terminals that have weights greater than or
equal to a predetermined threshold value may be extracted from
among the other communication terminals, and the lists of
candidates to be deleted of the extracted communication
terminals (the lists at the correspondent communication
10 terminals) may be used together with the list of candidate to be deleted of the local communication terminal Ala (the list at the local communication terminal). [0133]
On the basis of any of the determination methods
15 described above, the held information coordination unit A106 of the communication terminal Ala (node 1) identifies invalid information that does not need to be held and immediately deletes the invalid node information entries and routing information entries from the node information storage unit
20 A102 and the routing information storage unit A104 to avoid
uselessly holding the unnecessary node information entries and routing information entries of the communication terminals (sequence Seql3). Alternatively, the held information coordination unit A106 may set 'Time Out' or an 'invalid-entry
25 flag' in the expiration date and time 13 or the expiration date and time 43 of the invalid node information entries or routing information entries to control the node information exchange control unit AlOl or the routing information exchange control unit A103 to delete the node information entries or rouging

72 information entries in which 'Time Out' or the 'invalid-entry
flag' is set from the node information storage unit A102 or the
routing information storage unit A104 (sequence Seq 1 3).
[0134]
5 While an operation has been described in the description
of Fig. 8 that also uses information from another
communication terminal Alb (node 2) neighboring the
communication terminal Ala (node 1) and starts with exchange
of a notification of checking routing information, the same
10 process may be performed when exchanging a notification of checking node information, in which case the term routing information and the term node information in the foregoing description are interchanged. [0135]
15 Furthermore, while an operation has been described in
which the local communication terminal Ala (node 1) and the neighboring other communication terminal Alb (node 2) synchronize with each other to exchange checking notifications and lists of candidates to be deleted at substantially the same
20 time, there may be a lag between the timing of transmission of the checking notification from the communication terminal Ala (node 1) and the timing of transmission of the checking notification from the neighboring communication terminal Alb (node 2) within a predetermined allowable range in some cases.
25 [0136]
In such cases, the union of the lists of candidates to be deleted at the local communication terminal Ala and all of the neighboring other communication terminals described above may be used to identify invalid information that does not need

73 to be held. Specifically, first, a communication terminal at
which receipt of a checking notification has been delayed (for
example a communication terminal Ala (node 1) that has not
received a checking notification from a neighboring other
5 communication terminal Alb (node 2) within predetermined
time) performs an operation for deleting invalid information
that does not need to be held on the basis of a list of candidates
to be deleted (at the local communication terminal) that has
been generated and stored previously in the checking operation
10 in sequence SeqlO. [0137]
Then, upon receipt of a checking notification from the other correspondent communication terminal Alb (node 2) within predetermined time, the communication terminal sends
15 the stored list of candidates to be deleted (at the local
communication terminal) back to the other communication terminal Alb (node 2) as a list of candidates to be deleted (at the correspondent communication terminal). Then, upon receipt of a list of candidates to be deleted (at the
20 correspondent communication terminal) from the correspondent communication terminal Alb (node 2), the communication terminal may perform an operation for deleting invalid information that does not need to be held on the basis of the received list of candidates to be deleted.
25 [0138]
(Description of Operation of Second Embodiment)
An example of the control operation performed by the communication terminal Al illustrated in Fig. 7 as the second embodiment for preventing the communication terminal Al

74 from uselessly holding only one of a pair of a node information
entry and a routing information entry will be described below in
further detail with reference to the diagram of Fig. 8 and a
flowchart of Fig. 9. As stated previously, the diagram of Fig.
5 8 illustrates an example of the operation for deleting invalid
information that does not need to be held on the basis of only
the information at the communication terminal Ala (node 1) and
an example of the operation for deleting invalid information
that does not need to be held on the basis of a combination of a
10 list of candidates to be deleted (at the local communication terminal) generated by the communication terminal Ala (node 1) and a list of candidates to be deleted (at the correspondent communication terminal) generated by another communication terminal Alb (node 2).
15 [0139]
Fig. 9 is a flowchart for illustrating an example of the operation of the communication terminal Al illustrated in Fig. 7 as the second embodiment and illustrates an example of the operation for deleting invalid information by using only the
20 information in the local communication terminal Ala (node 1) in Fig. 8 for the sake of simplicity. Specifically, the flowchart of Fig. 9 illustrates an example of the operation in which the held information coordination unit A106 in the communication terminal Ala (node 1) in the diagram of Fig. 8
25 checks routing information entries corresponding to node
information entries stored in the node information storage unit A102 and node information entries corresponding to routing information entries stored in the routing information storage unit A104 at predetermined regular intervals and, if a node

75 information entry that corresponds to a routing information
entry does not exist or a routing information entry that
corresponds to a node information entry does not exist, or an
existing information entry has expired, the held information
5 coordination unit A106 deletes the information entry.
[0140]
Note that the process in the flowchart of Fig. 9 illustrates
an example in which the held information coordination unit
A106 checks node information and routing information at
10 predetermined regular intervals. While, as in the first
embodiment, the operation illustrated in the diagram of Fig. 8 and the flowchart of Fig. 9 is actually performed at each of the communication terminals that constitute a network as illustrated in any of Figs. 2A to 2D, the following description
15 will focus only on a communication terminal Ala (node 1) and another communication terminal Alb (node 2) illustrated in Fig. 8 among the communication terminals constituting the network, and be given on a case where an operation for exchanging node information and routing information between the two
20 communication terminals is performed for simplicity. [0141]
First, it is assumed that the communication terminal Ala (node 1) and the other communication terminal Alb (node 2) illustrated in Fig. 8 are within a range in which the two
25 communication terminals can communicate with each other and are interconnected through a wireless communication link LI, as described above. While a notification of checking node information may be received first or a notification of checking routing information may be received first in exchange of

76 notification of checking information between the
communication terminal Ala (node 1) and the other
communication terminal Alb (node 2), only a pattern in which a
notification of checking routing information is received first
5 will be described below in detail since the same operation is
performed for exchange of notifications of checking different
kinds of information as described previously with respect to
sequence Seqll in Fig. 8.
[0142]
10 In the diagram of Fig. 8, when the communication
terminal Ala (node 1) uses only the information in the communication terminal Ala (node) to delete invalid information that does not need to be held to prevent keeping uselessly holding only one of a pair of a node information entry
15 and a routing information entry, the operation described
previously with respect to sequence SeqlO is performed first. Specifically, the held information coordination unit A106 references node information NllO stored in the node information storage unit A102 of the communication terminal
20 Ala (node 1) and routing information RllO stored in the routing information storage unit A104 to check whether or not node information entries corresponding to the entries of the routing information RllO and routing information entries corresponding to the entries of the node information NllO exist
25 and check whether or not an entry that has expired exists,
thereby determining whether or not information is to be deleted
orkeptheld.
[0143]
When an information entry whose corresponding

77 information entry does not exist or an existing corresponding
information entry that has expired is detected, the held
information coordination unit A106 determines that the
information entry is invalid information and immediately
5 deletes the information entry as information to be deleted to
avoid uselessly holding or sets 'Time Out' or an 'invalid-entry
flag' indicating that the information entry is invalid to leave
the deletion of the invalid information to the node information
exchange control unit AlOl or the routing information exchange
1 0 control unit Al 03 . [0144]
Furthermore, if the communication terminal Ala (node 1) uses information in a neighboring other communication terminal Alb (node 2) in addition to the information in the
15 communication terminal Ala (node 1) to delete invalid
information that does not need to be held, the held information coordination unit A106 of the communication terminal Ala (node 1) exchanges checking notifications for checking whether invalid node information or invalid routing information exists
20 with the other communication terminal Alb (node 2) as
described previously with respect to sequence Seqll in Fig. 8 (the notification for checking routing information in the example in Fig. 8). [0145]
25 The held information coordination unit A106 of the
communication terminal Ala (node 1) receives the checking notification from the correspondent other communication terminal Alb (node 2), performs an operation similar to the checking operation in sequence SeqlO described previously

78 with respect to sequence Seql2 in Fig. 8, extracts invalid
information that does not need to be held, generates and stores
a list of candidates to be deleted (at the local communication
terminal), and sends the list of candidates to be deleted (at the
5 local communication terminal) as a list of candidates to be
deleted (at the correspondent communication terminal) back to
the correspondent other communication terminal Alb (node 2)
that has sent the checking notification.
[0146]
10 On the other hand, when the held information
coordination unit A106 of the communication terminal Ala (node 1) receives a list of candidates to be deleted (at the correspondent communication terminal) from the correspondent other communication terminal Alb (node 2), the held
15 information coordination unit A106 determines, on the basis of the combination of the received list of candidates to be deleted (at the correspondent communication terminal) and the stored list of candidates to be deleted (at the local communication terminal), whether or not information is invalid, and
20 immediately deletes information determined to be invalid to
avoid uselessly holding or sets 'Time Out' or an 'invalid-entry flag' indicating that the information is invalid in the node information storage unit A102 or the routing information storage unit A104 to leave the deletion of the invalid
25 information to the node information exchange control unit AlOl or the routing information exchange control unit A103 as described previously with respect to sequence Seql3 in Fig. 8. [0147]
An example of the operation of the held information

79 coordination unit A106 of the communication terminal Ala
(node 1) will be further described with reference to the
flowchart of Fig. 9. Note that in the following description,
the operation will be described in which the held information
5 coordination unit A106 of the communication terminal Ala
(node 1) uses only the information in the communication
terminal Ala (node 1) to determine whether information is
information to be held by the communication terminal Ala
(node 1) or invalid information that does not need to be held
10 and to be deleted, and immediately deletes a node information entry or routing information entry that is determined to be invalid information that does not need to be held and to be deleted from the node information storage unit A102 or the routing information storage unit A104 as described previously.
15 [0148]
In the second embodiment, in order to check for invalid information that does not need to be held at predetermined regular intervals as described above, the held information coordination unit A106 of the communication terminal Ala
20 (node 1) is activated to determine whether or not a node
information entry that corresponds to a routing information stored in the routing information storage unit A104 exists in the node information storage unit A102, or routing information entry that corresponds to a node information stored in the node
25 information storage unit A102 exists in the routing information storage unit A104, or whether or not an existing corresponding information entry has expired (step S200). [0149]
In the example illustrated in the diagram of Fig. 8, the

80 expiration date and time 13 of the node information entry
NllOy in the node information storage unit A102 that relates to
the communication terminal Y (node Y) with the same node IP
address 12 as the destination IP address 41 (Dest. IP address)
5 '192.168.0.3' of the routing information entry RllOy in the
routing information RllO stored in the routing information
storage unit A104 is 'Time Out', indicating expiration.
Accordingly, it is determined that the routing information entry
RllOy that has a destination IP address (Dest. IP address) 41 of
10 '192.168.0.3' and corresponds to the node information entry NllOy relating to the communication terminal Y (node Y) is invalid information that does not need to be held, and the routing information entry RllOy is placed on the list of candidates to be deleted and stored.
15 [0150]
The checking operation described above is performed for all of the node information entries stored in the node information storage unit A102 and all of the routing information entries stored in the routing information storage
20 unit A104 and, when checking as to whether or not
corresponding entries exist and whether or not entries have expired has been completed and a list of candidates to be deleted has been generated, the process proceeds to step S201. [0151]
25 Upon proceeding to step S201, the held information
coordination unit A106 references the list of candidates to be deleted which has been generated at step S200 to identify a node information entry or routing information entry that does not have a corresponding information entry or an existing

81 corresponding node information entry or routing information
entry that has expired as invalid information that does not need
to be held and deletes the information from the node
information storage unit A102 or the routing information
5 storage unit A104 (step S201). For example, in the diagram of
Fig. 8, the routing information entry RllOy (the routing
information entry with a destination IP address 41 (Dest. IP
address) of ' 1 92.1 6 8 .0. 3') corresponding to the node
information entry NllOy relating to the communication
10 terminal Y (node Y) that has expired is deleted. Note that the held information coordination unit A106 may set 'Time Out' or an "invalid-entry flag' in the expiration date and time 43 of the routing information entry RllOy at this point and may leave deletion of the routing information entry RllOy to the routing
15 information exchange control unit A103, instead of
immediately deleting the routing information entry RllOy. [0152]
By performing the operation described in the flowchart of Fig. 9, each communication terminal (each node) can "reduce
20 the transfer information amount of node information and
routing information exchanged with another communication terminal". Specifically, each communication terminal (each node) periodically discriminates between routing information, for example, to be held and invalid routing information that
25 does not need to be held, deletes routing information
determined to be invalid routing information that does not need to be held, and thus can avoid exchanging useless information with another communication terminal. [0153]

82 Consequently, when neighboring communication
terminals (for example the communication terminal Ala (node
1) and another communication terminal Alb (node 2) illustrated
in Fig. 8) periodically exchange routing information with each
5 other, the communication terminals can exchange valid routing
information alone, excluding routing information entries whose
corresponding node information entries have expired and which
cannot be used in information sharing, thereby avoiding useless
information exchange. Note that while exchange of routing
10 information between communication terminals has been
described here, the same operation is performed for exchanging node information. Furthermore, when corresponding information is checked, expiration of a node information entry is considered to be equivalent to absence of the entry as noted
15 above. In the case of a routing information entries, not only a routing information entry that has expired but also a routing information entry whose route score is less than or equal to a predetermined threshold value is considered to be equivalent to a missing entry as noted above.
20 [0154]
(Configuration of Third Embodiment)
A third embodiment of the present invention will be described next in detail with reference to block diagram of Fig. 10. Fig. 10 is a block diagram illustrating an exemplary block
25 configuration of the third embodiment of a communication terminal according to the present invention. [0155]
In the communication terminal Al in Fig. 1 described previously as the first embodiment, node information or routing

83 information is exchanged on the basis of whether or not
corresponding information entries between node information
and routing information exist to acquire both of the node
information and routing information at substantially the same
5 time and information in the node information storage unit A102
and information in the routing information storage unit A104
are updated. In the communication terminal Al in Fig. 7
described previously as the second embodiment, determination
is made as to whether or not a node information entry or a
10 routing information entry is to be held by the communication terminal Al on the basis of whether or not corresponding information entries between node information and routing information exist and, if it is determined that the information entry is not to be held, the information entry is deleted from the
15 node information storage unit A102 or the routing information storage unit A 1 04. [0156]
The communication terminal Al of the third embodiment illustrated in Fig. 10 is characterized by having the capability
20 of performing the operation of the first embodiment and the operation of the second embodiment in combination. [0157]
Accordingly, the communication terminal Al of the third embodiment illustrated in Fig. 10 includes both of the
25 information exchange coordination unit A105 of the
communication terminal Al of the first embodiment illustrated in Fig. 1 and the held information coordination unit A106 of the communication terminal Al of the second embodiment illustrated in Fig. 7. The functions of the information

84 exchange coordination unit A105 and the held information
coordination unit A106 are the same as the functions described
in the first embodiment and the second embodiment,
respectively, and the repeated description of those functions
5 will be omitted here.
[0158]
(Description of Operation of Third Embodiment)
An example of an operation in which the communication
terminal Al illustrated in Fig. 10 as a third embodiment
10 performs control to acquire both of node information and routing information at substantially the same time and an example of an operation in which the communication terminal Al performs control to avoid uselessly holding only one of a pair of a node information entry and a routing information entry
15 will be described next in detail with reference to the diagram of Fig. 5, the flowchart of Fig. 6, the diagram of Fig. 8 and the flowchart of Fig. 9 described previously. [0159]
Operation of the communication terminal Al of the third
20 embodiment illustrated in Fig. 10 will be described first with reference to the diagram of Fig. 5. Like the communication terminal Ala (node 1) illustrated in the diagram of Fig. 5 as the first embodiment, the communication terminal Al illustrated in Fig. 10 uses an information exchange coordination unit A105 to
25 monitor node information and routing information at
predetermined regular intervals to determine the timings of exchanging node information and routing information. Specifically, upon detecting update of only one of a pair of a node information entry and a routing information entry that

85 correspond to each other, the information exchange
coordination unit A105 immediately performs an operation for
acquiring the corresponding other information entry from a
neighboring other communication terminal Alb to control to
5 acquire both of the node information entry and the routing
information entry that correspond to each other at substantially
the same time and update the node information and the routing
information, as illustrated in the diagram of Fig. 5 and the
flowchart of Fig. 6 as the first embodiment.
10 [0160]
Furthermore, like the communication terminal Ala (node 1) illustrated in the diagram of Fig. 8 as the second embodiment, the communication terminal Al illustrated in Fig. 10 uses a held information coordination unit A106 to check node
15 information entries and routing information entries that
correspond with each other at predetermined regular intervals to determine whether an information entry is an information entry to be held or an invalid information entry that does not need to be held.
20 [0161]
Specifically, as illustrated in the diagram of Fig. 8 and the flowchart of Fig. 9 as the second embodiment, when the held information coordination unit A106 uses only information in the local communication terminal to determine whether or not
25 an information entry is to be held, the held information
coordination unit A106 checks node information entries and routing information entries that are stored in the communication terminal and correspond to each other and, if a corresponding information entry does not exist or an existing

86 corresponding information entry has expired, the held
information coordination unit A106 determines that the
information entry is an invalid information entry that does not
need to be held and deletes the information entry from the node
5 information storage unit A102 or the routing information entry
A104.
[0162]
Furthermore, as described with respect to the diagram of
Fig. 8, when the held information coordination unit A106 also
10 uses information in other communication terminals to determine whether or not an information entry is to be held, the held information coordination unit A106 exchange a notification of checking node information and routing information with all neighboring other communication terminals. Upon receipt of
15 the checking notification, the held information coordination unit A106 extracts an information entry that does not have a corresponding information entry at the local communication terminal or an information entry that has expired as an invalid information entry that does not need to be held, places the
20 information entry on a list of candidates to be deleted (at the local communication terminal), stores the list, and sends the list of candidates to be deleted (at the local communication terminal) as a list of candidates to be deleted (at a correspondent communication terminal) back to the other
25 communication terminal that has sent the checking notification. [0163]
Moreover, upon receipt of a list of candidates to be deleted (at the correspondent communication terminal) from the correspondent other communication terminal to which the

87 checking notification has been sent, the held information
coordination unit A106 uses the combination of the received
list of candidates to be deleted (at the correspondent
communication terminal) and the stored list of candidates to be
5 deleted (at the local communication terminal) to identify an
invalid information entry that does not need to be held and
deletes the information entry from the node information storage
unit A102 or the routing information storage unit A104.
[0164]
10 In the communication terminal of the third embodiment
that performs the operation described above, the provision of both of the information exchange coordination unit A105 and the held information coordination unit A106 not only enables the communication terminal to be placed in a "state where both
15 of node information and routing information are managed in association with each other or a state where both of the two kinds of information are held" but also enables "reduction in the transfer information amount of node information and routing information exchanged with other communication
20 terminals". [0165]
Configurations of preferred embodiments of the present invention have been described. However, it should be noted that the embodiments are illustrative of the present invention
25 and are not intended to limit the present invention. It will be understood by those skilled in the art that various variations and modification can be made for adaptation to specific applications without departing from the scope of the present invention.

88 [0166]
This application is based upon and claims the benefit of
priority of Japanese Patent Application No. 2012-224131, filed
on October 9, 2012, the entire disclosure of which is
5 incorporated herein.
[Reference signs List] [0167]
11 ... Node ID 10 12 ... Node IP address
13 ... Entry expiration date and time
21 ... Node ID
22 ... Routing Address
23 ... Entry expiration date and time 15 31 ... Node ID

32 ... Node IP address
33 ... Contents list
34 ... Entry expiration date and time 41 ... Destination IP address
20 42 ... Next-hop IP address
43 ... Entry expiration date and time
51 ... Destination IP address
52 ... Next-hop IP address
53 ... Entry receipt time
25 61 ... Destination IP address
62 ... Next-hop IP address
63 ... Route score
Al ... Communication terminal
AlOO ... Wireless communication function unit

89 AlOl ... Node information exchange control unit
A102 ... Node information storage unit
A103 ... Routing information exchange control unit
A104 ... Routing information storage unit 5 A105 ... Information exchange coordination unit
A106 ... Held information coordination unit
Ala ... Node 1 (local communication terminal)
Alb ... Node 2 (other communication terminal)
Bl ... Communication terminal 10 LI ...Wireless communication link
NlOO ... Node information held by node A
NlOOy ... Entry of node Y in node information held by node A
NllO ... Node information held by node 1
NllOy ... Entry of node Y in node information held by node 1 15 N120, N130 ... Node information
PI ... Node information non-holding period
P2 ... Routing information non-holding period
RlOO ... Routing information held by node A
RlOOy ... Entry of node Y in routing information held by node A 20 RllO ... Routing information held by node 1
RllOy ... Entry of node Y in routing information held by node 1
R120, R130 ... Routing information
SlOO - S103 ... Process steps at information exchange coordination unit
of first embodiment 25 S200, S201 ... Process steps at held information coordination unit of
second embodiment
Tl, T2 ... Messaging timing

WE CLAIMS:-
A method for exchanging information between
communication terminals, the method comprising exchanging
node information and routing information between a plurality
of communication terminals constituting a network, the node
information being used for identifying each of the
communication terminals, the routing information indicating a
communication route to each of the communication terminals
which is a destination;
wherein when each of the plurality of communication terminals detects, in the routing information locally held by the communication terminal, update of a routing information entry relating to any of the communication terminals or detects, in
the node information locally held by the communication
terminal, update of a node information entry relating to any of the communication terminal,
the communication terminal references, in the node information locally held by the communication terminal, a node
information entry corresponding to the updated routing
information entry or, references, in the routing information locally held by the communication terminal, a routing information entry corresponding to the updated node information entry; and
if the corresponding node information entry or the
corresponding routing information entry does not exist, acquires the corresponding node information entry or the corresponding routing information entry from another communication terminal.

[Claim 2]
A method for exchanging information between
communication terminals, the method comprising exchanging
node information and routing information between a plurality
of communication terminals constituting a network, the node
information being used for identifying each of the
communication terminals, the routing information indicating a
communication route to each of the communication terminals
which is a destination;
wherein when each of the plurality of communication
terminals determines whether or not each of the routing information entries relating to the communication terminals that are included in the routing information locally held by the communication terminal or each of the node information entries
relating to the communication terminals that are included in the node information locally held by the communication terminal is information to be held,
the communication terminal references, in the node information locally held by the communication terminal, a node
information entry corresponding to each of the routing
information entries or references, in the routing information locally held by the communication terminal, a routing information entry corresponding to each of the node information entries; and
if a node information entry corresponding to the routing
information entry does not exist, the communication terminal deletes the relevant routing information entry from the routing information locally held by the communication terminal, or if a routing information entry corresponding to the node

information entry does not exist, the communication terminal
deletes the relevant node information entry from the node
information locally held by the communication terminal.
[Claim 3]
A method for exchanging information between
communication terminals, the method comprising exchanging
node information and routing information between a plurality
of communication terminals constituting a network, the node
information being used for identifying each of the
communication terminals, the routing information indicating a communication route to each of the communication terminals which is a destination;
wherein when each of the plurality of communication terminals determines whether or not each of the routing
information entries relating to the communication terminals
that are included in the routing information locally held by the communication terminal or each of the node information entries relating to the communication terminals that are included in the node information locally held by the communication terminal is
information to be held,
the communication terminal references, in the node information locally held by the communication terminal, a node information entry corresponding to each of the routing information entries or references, in the routing information
locally held by the communication terminal, a routing information entry corresponding to each of the node information entries; and
if a node information entry corresponding to the routing information entry does not exist, the communication terminal

places the relevant routing information entry on an own list of
candidates to be deleted at the communication terminal, stores
the own list of candidates to be deleted at the communication
terminal, and sends the own list of candidates to be deleted at
the communication terminal to another communication terminal
as a list of candidates to be deleted at a correspondent
communication terminal, or if a routing information entry
corresponding to each of the node information entries does not
exist, places the relevant node information entry on an own list
of candidates to be deleted at the communication terminal, stores the own list of candidates to be deleted at the communication terminal, and sends the own list of candidates to be deleted at the communication terminal to another communication terminal as a list of candidates to be deleted at
a correspondent communication terminal;
when the communication terminal receives the list of candidates to be deleted at the correspondent communication terminal from another communication terminal, the communication terminal determines, on the basis of a
combination of the routing information entry or the node
information entry placed on the received list of candidates to be deleted at the correspondent communication terminal and the routing information entry or the node information entry placed on the stored own list of candidates to be deleted at the
communication terminal, whether or not each of the routing
information entries locally held by the communication terminal is to be kept held or whether or not each of the node information entries locally held by the communication terminal is to be kept held; and

the communication terminal deletes the routing
information entry determined to be invalid information that
does not need to be kept held from the routing information
locally held by the communication terminal, or deletes the node
information entry determined to be invalid information that
does not need to be kept held from the node information held
locally by the communication terminal.
[Claim 4]
The method for exchanging information between
communication terminals according to Claim 3,
wherein each of the plurality of communication terminals determines that the routing information entry that is placed on all of the lists of candidates to be deleted at the correspondent communication terminal and the own list of
candidates to be deleted at the communication terminal, or the routing information entry that is placed on at least one of the lists of candidates to be deleted at the correspondent communication terminal and the own list of candidates to be deleted at the communication terminal is an invalid routing
information entry that does not need to be kept held; or each of the plurality of communication terminals determines that the node information entry placed on all of the lists of candidates to be deleted at the correspondent communication terminal and the own list of candidates to be
deleted at the communication terminal, or the node information entry placed on at least one of the lists of candidates to be deleted at the correspondent communication terminal and the own list of candidates to be deleted at the communication

terminal is an invalid node information entry that does not need
to be kept held.
[Claim 5]
The method for exchanging information between communication terminals according to any one of Claims 1 to 4,
wherein cases where a node information entry corresponding to the routing information entry does not exist includes at least a case where an amount of time greater than or equal to a period of time predetermined as an expiration date and time of the node information entry has passed; and
cases where a routing information entry corresponding to the node information entry does not exist includes at least a case where an amount of time greater than or equal to a period of time predetermined as an expiration date and time of the routing information entry has passed or a case where a route score, which is a value indicating reachability to the communication terminal corresponding to the routing information entry, is less than or equal to a predetermined threshold value.
[Claim 6]
A communication terminal which exchanges node information and routing information with one or more other communication terminals constituting a network, the node information being used for identifying each of a plurality of communication terminals, the routing information indicating a communication route to each of communication terminals which is a destination, the communication terminal comprising at least means for:

upon detection of update of a routing information entry
relating to any of the communication terminals in the routing
information held by the communication terminal or update of a
node information entry relating to any of the communication
terminals in the node information held by the communication
terminal,
referencing, in the node information held by the
communication terminal, a node information entry
corresponding to the updated routing information entry or,
referencing, in the routing information held by the communication terminal, a routing information entry corresponding to the updated node information entry; and if the corresponding node information entry or the corresponding routing information entry does not exist,
acquiring the corresponding node information entry or the corresponding routing information entry from another communication terminal.
[Claim 7]
A communication terminal which exchanges node
information and routing information with one or more other communication terminals constituting a network, the node information being used for identifying each of a plurality of communication terminals, the routing information indicating a communication route to each of communication terminals which
is a destination, the communication terminal comprising at least means for:
when determining whether or not each of the routing information entries relating to the communication terminals that are included in the routing information held by the

communication terminal or each of the node information entries
relating to the communication terminals that are included in the
node information held by the communication terminal is
information to be held,
referencing, in the node information locally held by the
communication terminal, a node information entry
corresponding to each of the routing information entries or
referencing, in the routing information locally held by the
communication terminal, a routing information entry
corresponding to each of the node information entries; and
if a node information entry corresponding to the routing information entry does not exist, deleting the relevant routing information entry from the routing information locally held by the communication terminal, or if a routing information entry
corresponding to the node information entry does not exist, deleting the relevant node information entry from the node information locally held by the communication terminal.
[Claim 8]
A communication terminal which exchanges node
information and routing information with one or more other communication terminals constituting a network, the node information being used for identifying each of a plurality of communication terminals, the routing information indicating a communication route to each of communication terminals which
is a destination, the communication terminal comprising at least means for:
when determining whether or not each of the routing information entries relating to the communication terminals that are included in the routing information held by the

communication terminal or each of the node information entries
relating to the communication terminals that are included in the
node information held by the communication terminal is
information to be held,
referencing, in the node information held by the
communication terminal, a node information entry
corresponding to each of the routing information entries or
referencing, in the routing information held by the
communication terminal, a routing information entry
corresponding to each of the node information entries; and
if a node information entry corresponding to the routing information entry does not exist, placing the relevant routing information entry on an own list of candidates to be deleted at the communication terminal, storing the own list of candidates
to be deleted at the communication terminal, and sending the own list of candidates to be deleted at the communication terminal to another communication terminal as a list of candidates to be deleted at a correspondent communication terminal, or if a routing information entry corresponding to
each of the node information entries does not exist, placing the relevant node information entry on an own list of candidates to be deleted at the communication terminal, storing the own list of candidates to be deleted at the communication terminal, and sending the own list of candidates to be deleted at the
communication terminal to another communication terminal as a list of candidates to be deleted at a correspondent communication terminal;
when the communication terminal receives the list of candidates to be deleted at the correspondent communication

terminal from another communication terminal, determining, on
the basis of a combination of the routing information entry or
the node information entry placed on the received list of
candidates to be deleted at the correspondent communication
terminal and the routing information entry or the node
information entry placed on the stored own list of candidates to
be deleted at the communication terminal, whether or not each
of the routing information entries held by the communication
terminal is to be kept held or whether or not each of the node
information entries held by the communication terminal is to be kept held; and
deleting the routing information entry determined to be invalid information that does not need to be kept held from the routing information held by the communication terminal, or
deleting the node information entry determined to be invalid information that does not need to be kept held from the node information held by the communication terminal.
[Claim 9]
The communication terminal according to Claim 8,
wherein the communication terminal determines that the
routing information entry that is placed on all of the lists of candidates to be deleted at the correspondent communication terminal and the own list of candidates to be deleted at the communication terminal, or the routing information entry that
is placed on at least one of the lists of candidates to be deleted at the correspondent communication terminal and the own list of candidates to be deleted at the communication terminal is an invalid routing information entry that does not need to be kept held; or

100 the communication terminal determines that the node
information entry placed on all of the lists of candidates to be
deleted at the correspondent communication terminal and the
own list of candidates to be deleted at the communication
terminal, or the node information entry placed on at least one of
the lists of candidates to be deleted at the correspondent
communication terminal and the own list of candidates to be
deleted at the communication terminal is an invalid node
information entry that does not need to be kept held.
[Claim 10]
The communication terminal according to any one of Claims 6 to 9,
wherein cases where a node information entry corresponding to the routing information entry does not exist
includes at least a case where an amount of time greater than or equal to a period of time predetermined as an expiration date and time of the node information entry has passed; and
cases where a routing information entry corresponding to the node information entry does not exist includes at least a
case where an amount of time greater than or equal to a period of time predetermined as an expiration date and time of the routing information entry has passed or a case where a route score, which is a value indicating reachability to the communication terminal corresponding to the routing
information entry, is less than or equal to a predetermined threshold value.