DESCRIPTION
COMMUNICATION SYSTEM
TECHNICAL FIELD
The present invention relates to a communication system and to components thereof for
providing relay services to mobile or fixed communication devices. The invention has particular
but not exclusive relevance to relay services used in LTE-Advanced as currently defined in
3GPP standards documentation TS 36.413 V 9.3.0 and TS 36-300 V 10.0.0.
BACKGROUND ART
Relaying is considered for LTE-Advanced as a tool to improve, for example, the
coverage of high data rates for User Equipment (UE), group mobility, temporary network
deployment, the cell edge throughput and/or to provide coverage in new cell areas. E-UTRAN
supports relaying by having a Relay Node (RN) wirelessly connected to a base station (eNB)
(referred to as a Donor eNB (DeNB)). In addition to serving its own 'donor' cell, the Donor
eNB serves the RN, via a modified version of the E-UTRA radio interface. The modified
interface is referred to as the 'Un' interface.
Each RN is provided with many aspects of a base station's functionality and is therefore
capable of acting as a base station serving its own 'relay' cell. From the perspective of the user
equipment in the relay cell, therefore, the RN essentially appears to be a conventional LTE base
station. In addition to the base station functionality, however, the RN also supports a subset of
the UE functionality including, for example, many aspects of the physical layer, layer-2, radio
resource control (RRC), and non access stratum (NAS) functionality, to allow it to connect
wirelessly to a Donor eNB.
Several mobility management entities (MMEs) are located in the core of the E-UTRA
network. Each MME serves a respective subset of the user equipment in the 'donor' cell of the
Donor eNB, the relay cell, and/or other cells in the wider network. The Donor eNB forwards
control messages received from the MME to the RN over the Un interface and, from the
perspective of the RN, the Donor eNB appears to be a single MME that serves all the items of
user equipment registered with the RN in the relay cell.
Accordingly, the Donor eNB is capable of handling communication both 'directly' to and
from user equipment camped in its own cell and 'indirectly', via the RN, to and from user
equipment camped in the relay cell.
The MMEs in the core network can become overloaded and, accordingly, each MME is
provided with an overload handling capability. Specifically, when one of the MMEs experiences
an overload situation, it randomly selects a subset of the base stations that it communicates with,
and sends the selected base station(s) a control message to request initiation of a procedure to
alleviate the overload situation. Typically, for example, the requested overload procedure will
involve the base station rejecting attempts to establish a connection made by user equipment
served by the MME making the request.
SUMMARY OF THE INVENTION
The inventors have, however, realised that there is a problem with this arrangement. In
particular, when a Donor eNB receives an overload initiation message from an MME it initiates
the overload procedure for user equipment in its own donor cell. The Donor eNB also forwards
the overload initiation message to the RN. However, because the Donor eNB appears, to the RN,
to be a single MME that serves all the user equipment in the relay cell, the relay node responds
to the overload message by initiating the overload procedure for all the user equipment camped
in its relay cell. Thus, in addition to rejecting attempts to establish a connection made by user
equipment served by the overloaded MME, the relay node will also reject connection attempts
made by user equipment served by other MMEs regardless of whether the other MMEs are
overloaded or not. Thus, attempts by user equipment in the relay cell to establish a connection
via the RN may be rejected unnecessarily. This can result in an undesirably high incidence of
connection rejections in the relay cell.
The present invention aims to provide an improved communication system and improved
components of the communication system which overcome or at least alleviate the above issues.
Accordingly one aspect of the present invention provides a relay node for a
communication system, the relay node comprising: means for associating a plurality of mobile
devices with the relay node; means for receiving, from a base station, a request that an overload
action be performed and identity information representing an identity of a network entity that
requested the overload action; and means for selectively performing said requested overload
action in respect of the mobile devices associated with the relay node in dependence on whether
or not the mobile devices are served by the network entity having the identity represented by the
identity information.
The requested overload action may comprise initiating an overload procedure. The
request for initiating an overload procedure may comprise overload start message (e.g. an SI AP:
Overload Start Message).
The network entity may comprise a mobility management entity (MME).
The overload procedure may comprise receiving a request to establish a connection from
a mobile telephone associated with the relay node, may comprise determining whether or not the
mobile telephone that made the request is served by the network entity having the identity
represented by the identity information, may comprise generating a message for rejecting said
request to establish a connection or generating a message for accepting said request to establish a
connection in dependence on whether or not the mobile telephone that made the request is served
by the network entity having the identity represented by the identity information, and/or may
comprise transmitting said generated message to the mobile telephone that made the request to
establish a connection.
The overload procedure initiated by the performing means may further comprise
determining a reason for the requested connection establishment request, and wherein said
generation step may further comprise generating said message for rejecting said request to
establish a connection or generating said message for accepting said request to establish a
connection in dependence on said determined reason for the requested connection.
The requested overload action may comprise terminating an overload procedure. The
request for terminating an overload procedure may comprise overload stop message (e.g. an SI
AP: Overload Stop Message)
Another aspect of the present invention provides a base station for a communication
system, the base station comprising: means for receiving, from a network entity, a request that an
overload action be performed; means for generating identity information representing an identity
of the network entity that requested the overload action; and means for transmitting, to a relay
node, the request that the overload action be performed and the information representing an
identity of the network entity that requested the overload actioa
The base station may further comprise means for inserting said information representing
an identity of the network entity that requested the overload action into said request that the
overload action be performed, whereby said information representing an identity of the network
entity that requested the overload action may be transmitted as part of said request that the
overload action be performed.
The request that the overload action be performed may comprise a request for an
overload procedure to be initiated (e.g. an Overload Start message).
The request that the overload action be performed may comprise a request for an
overload procedure to be terminated (e.g. an Overload Stop message).
According to another aspect of the invention there is provided a network entity for a
communication system, the network entity comprising: means for determining that an overload
situation has occurred; means for generating, in response to determining that an overload
situation has occurred, a request that an overload action be performed, said request comprising
information representing an identity of the network entity (e.g. in an information element such as
an MME ID IE); and means for transmitting, to a base station, the request that the overload
action be performed.
According to another aspect of the invention there is provided a method performed by a
relay node in a communication system, the method comprising: associating a plurality of mobile
devices with the relay node; receiving, from a base station, a request that an overload action be
performed and identity information representing an identity of a network entity that requested the
overload action; and selectively performing said requested overload action in respect of the
mobile devices associated with the relay node in dependence on whether or not the mobile
devices are served by the network entity having the identity represented by the identity
information.
According to another aspect of the invention there is provided a method performed by a
base station in a communication system, the method comprising: receiving, from a network
entity, a request that an overload action be performed; generating identity information
representing an identity of the network entity that requested the overload action; and transmitting,
to the relay node, the request that the overload action be performed and the information
representing an identity of the network entity that requested the overload action.
According to another aspect of the invention there is provided a method performed by a
network entity for a communication system, the method comprising: determining that an
overload situation has occurred; generating, in response to determining that an overload situation
has occurred, a request that an overload action be performed, said request comprising
information representing an identity of the network entity; and transmitting, to a base station, the
request that the overload action be performed.
According to another aspect of the invention there is provided a communications device
for a communication system that comprises a plurality of network entities, a base station, a relay
node, and a plurality of mobile devices associated with the relay node, the communications
device comprising: means for receiving a request that an overload action be performed for at
least one of said plurality of network entities; and means for selectively performing said
requested overload action in respect of the mobile devices associated with the relay node in
dependence on whether or not the mobile devices are served by the network entity for which the
overload action has been requested.
The communications device may be said relay node or may be said base station.
The requested overload action may comprise initiating an overload procedure, and said
overload procedure may comprise receiving a request to establish a connection from a mobile
telephone associated with the relay node, may comprise determining whether or not the mobile
telephone that made the request is served by the network entity for which the overload action
was requested, may comprise generating a message for rejecting said request to establish a
connection or generating a message for accepting said request to establish a connection in
dependence on whether or not the mobile telephone that made the request is served by the
network entity for which the overload action was requested, and/or may comprise transmitting
said generated message to the mobile telephone that made the request to establish a connection.
The requested overload action may comprise initiating an overload procedure, and said
overload procedure may comprises receiving an indication that a connection has been established
between a mobile telephone associated with the relay node and the relay node, may comprise
determining whether or not the mobile telephone for which the connection is established is
served by the network entity for which the overload action has been requested, may comprise
selectively generating a message for terminating said established connection in dependence on
whether or not the mobile telephone for which the connection is established is served by the
network entity for which the overload action has been requested, and/or may comprise
transmitting any message so generated to the relay node.
The message for terminating said established connection may comprise an error
indication and/or may comprise a message for releasing a context of the mobile telephone. A
message for releasing a context may comprise a UE Context Release.
According to another aspect of the invention there is provided a method performed by a
communications device in a communication system that comprises a plurality of network entities,
a base station, a relay node, and a plurality of mobile devices associated with the relay node, the
method comprising: receiving a request that an overload action be performed for at least one of
said plurality of network entities; and selectively performing said requested overload action in
respect of the mobile devices associated with the relay node in dependence on whether or not the
mobile devices are served by the network entity for which the overload action is requested.
According to another aspect of the invention there is provided a computer program
product comprising computer implementable instructions for causing a programmable computer
device to become configured as the relay node, as the base station, as the network entity, or as
the communications device.
A preferable embodiment of the invention extends to methods and/or apparatus
substantially as herein described with reference to the accompanying drawings.
Any feature in one aspect of the invention may be applied to other aspects of the
invention, in any appropriate combination. In particular, method aspects may be applied to
apparatus aspects, and vice versa.
Furthermore, features implemented in hardware may generally be implemented in
software, and vice versa. Any reference to software and hardware features herein should be
construed accordingly.
The invention also provides corresponding methods and computer software products that
may be provided on a carrier signal or on a recording medium.
The text of the abstract filed herewith is repeated here as part of the specification. In an
exemplary aspect of the invention of the invention there is provided a relay communications
system in which a base station receives a request from an MME that an overload procedure be
started or stopped. The base station inserts the identity of the MME into the request and
forwards the modified request to a relay node. The relay node then initiates or terminates the
overload procedure in accordance with the request for mobile telephones which the MME that
made the request serves, but not for mobile telephones which the MME does not serve.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of example only, with
reference to the attached figures in which:
Figure 1 schematically illustrates a mobile telecommunication system of a type to which
the described embodiments are applicable;
Figure 2 is a block diagram illustrating the main components of the base station illustrated in
Figure 1;
Figure 3 is a block diagram illustrating the main components of the relay station
illustrated in Figure 1;
Figure 4 is a flow diagram illustrating, in general terms, a procedure for initiating a
response to an overload situation performed by components of the mobile telecommunication
system of Figure 1;
Figure 5 is a flow diagram illustrating, in general terms, a procedure for terminating a
response to an overload situation performed by components of the mobile telecommunication
system of Figure 1;
Figure 6 is a flow diagram illustrating, in general terms, an overload procedure performed
by components of the mobile telecommunication system of Figure 1; and
Figure 7 is a simplified overview of a mobile telecommunication system of a type to
which the described embodiments are applicable.
MODE OF CARRYING OUT THE INVENTION
Overview
Figure 1 schematically illustrates a mobile (cellular) telecommunication system 1
including user equipment 3, comprising a plurality of mobile telephones 3-1 to 3-5 served by a
donor base station 5-1, and user equipment 4 comprising a plurality of other mobile telephones
4-1 to 4-3 served by another base station 5-2. The telecommunication system 1 also comprises a
relay node 7 that connects wirelessly to the donor base station 5-1, and a core network 8
including, amongst other things, a plurality of mobility management entities (MMEs) 9-1, 9-2, 9-
3 (generally referenced as 9).
Each MME 9 serves a different subset of the mobile telephones 3, 4, via a respective base
station 5-1, 5-2. In Figure 1, for example, mobile telephones 3-3, 3-4 and 4-3 are served by
MME 9-1, mobile telephones 3-1, 3-5 and 4-1 are served by MME 9-2, and mobile telephones 3-
2 and 4-2 are served by MME 9-3. Each MME 9 may also serve other mobile telephones via
other base stations that are not shown in Figure 1.
Mobile telephones 3-1, 3-2, and 4 (hereafter referred to as Direct MTs) are each
registered directly with a respective base station 5-1, 5-2. Mobile telephones 3-3, 3-4 and 3-5
(hereafter referred to as Relay MTs) are registered with the relay node 7. Accordingly, users of
mobile telephones 3-1 and 3-2 can communicate with other users via the donor base station 5-1
and the core network 8. Users of mobile telephones 3-3 to 3-5 can communicate with other users
via the relay node 7 and the donor base station 5-1 and the core network 8. Users of the other
mobile telephones 4 can communicate with other users via the other base station 5-2 and the core
network 8.
To help ensure that the communication protocols used by the Relay MTs 3-3, 3-4 and 3-5
and the Direct MTs remain consistent with one another, the relay node 7 effectively appears to
be a base station to the Relay MTs 3-3, 3-4 and 3-5. Similarly, the base station 5 effectively
appears to be an MME to the relay node 7.
When an MME 9 experiences an overload situation, it randomly selects at least one of the
base stations 5 via which the mobile telephones 3, 4 that it serves are registered (either directly
via a base station 5 or indirectly via the relay node), to initiate a corresponding overload
procedure. The overloaded MME 9 generates an 'overload start' message comprising an
indication of the actions required in response to the overload situation, and sends it to the
selected base station(s) 5 to request initiation of the corresponding overload procedure. When
the overloaded MME 9 is no longer overloaded it generates an Overload stop' message
indicating that the requested overload procedure is no longer required and can therefore be
discontinued.
In this embodiment, an MME 9 is able to request initiation of any of three different types
of overload procedure by generating an overload start message including information identifying
which of the three types of procedure is required. The different overload procedures which can
be requested in this manner comprise:
• Rejection of all attempts to establish connections for non-emergency mobile
originated data transfer;
• Rejection of all attempts to establish signalling connections; and
• Permitting attempts to establish connections for emergency sessions and mobile
terminated services only.
When the donor base station 5-1 has been selected by an MME 9 to initiate an overload
procedure, and has received the associated overload start message, it initiates the requested
overload procedure in respect of any Direct MTs 3-1 and 3-2 served by the overloaded MME 9.
The donor base station 5-1 also inserts information identifying the sending MME 9 into the
overload start message and forwards the modified overload start message (including the
information identifying the sending MME 9) to the relay node 7. The relay node 7 reads the
MME identification information provided with the overload start message and initiates the
requested overload procedure only for the specific Relay MTs 3-3, 3-4 and 3-5 served by the
overloaded MME 9 represented by the MME identification information read from the overload
start message.
Accordingly, the relay node 7 is advantageously able to perform the actions required in
response to the overload situation, selectively, for any Relay MTs 3-3 to 3-5 that the overloaded
MME 9 serves, whilst any Relay MTs 3-3 to 3-5 served by an MME 9 that is not overloaded, are
unaffected.
When the donor base station 5-1 receives an overload stop message it terminates the
requested overload procedure in respect of any Direct MTs 3-1, 3-2 served by the MME 9 from
which it has received the overload stop message. The donor base station 5-1 also inserts
information identifying the sending MME 9 into the overload stop message and forwards the
modified overload stop message (including the information identifying the sending MME 9) to
the relay node 7. The relay node 7 reads the MME identification information sent with the
overload stop message and discontinues the overload procedure only for any Relay MTs 3-3 to
3-5 served by the MME 9 that sent the original overload stop message.
Accordingly, when a relay node 7 is carrying out parallel overload procedures in respect
of a plurality of MMEs 9, the relay node 7 is advantageously able to selectively discontinue the
overload procedure for mobile telephones 3-3 to 3-5 served by an MME 9 that ceases to be
overloaded, without affecting the other parallel overload procedure(s) for other MME(s) 9.
Base station
Figure 2 is a block diagram illustrating the main components in the donor base station 5-1
shown in Figure 1. As shown, the donor base station 5-1 includes a transceiver circuit 3 1 which
is operable to transmit signals to, and to receive signals from, the Direct MTs 3-1 and 3-2 and the
relay node 7 via at least one antenna 3. The donor base station 5-1 is also operable to transmit
signals to and to receive signals from the MMEs 9 of the core network 8 via a network interface
35. The operation of the transceiver circuit 31 is controlled by a controller 37 in accordance with
software stored in memory 39.
The software includes, among other things, an operating system 41, a communications
control module 43, an MME overload management module 45, an overload message handling
module 47, and a Radio Resource Control (RRC) message handling module 49.
The communications control module 43 is operable to control communication with the
Direct MTs 3-1 and 3-2 and the relay node 7 including, for example, allocation of resources to be
used by the transceiver circuit 31 in its communications with each of the Direct MTs 3-1 and 3-2
and with the relay node 7. The communications control module 43 also schedules the times for
the transmission of downlink data to the Direct MTs 3-1 and 3-2 and the relay node 7.
The MME overload management module 45 initiates MME overload procedures, in
accordance with the required overload actions indicated in associated overload start messages
received from overloaded MMEs 9, in respect of the Direct MTs 3-1 and 3-2 served by the
overloaded MMEs 9. Similarly, the MME overload management module 45 terminates MME
overload procedures, in accordance with overload stop messages received from MMEs 9 that
cease to be overloaded, for the Direct MTs 3-1 and 3-2 served by those MMEs 9.
The overload message handling module 47 receives overload messages (both start and
stop messages) and extracts any information required by the MME overload management
module 45 to initiate/terminate the MME overload procedures for the Direct MTs 3-1 and 3-2
(e.g. information identifying the type of overload actions required). The overload message
handling module 47 also identifies the MME 9 from which each overload message is received,
inserts an identifier for the MME 9 which sent the overload message into an MME identification
information element provided in the overload message, and forwards the modified message to
the relay node 7.
The RRC message handling module 49 handles RRC messages received from the Direct
MTs 3-1 and 3-2 by interpreting the RRC messages and responding to the messages
appropriately. When an overload procedure has been initiated for an overloaded MME 9, the
RRC message handling module 49 responds to RRC connection establishment messages
received from Direct MTs 3-1 and 3-2, by determining whether or not the message has been
received from a mobile telephone 3 served by the overloaded MME 9. If a message has been
received from a mobile telephone 3 served by the overloaded MME 9, then the RRC message
handling module 49 responds by generating a corresponding RRC message to reject or permit
the connection attempt in dependence on the type of overload procedure requested by the
overloaded MME 9 and the reason for the connection establishment message.
Relay Node
Figure 3 schematically illustrates the main components of the relay node 7 shown in
Figure 1. The relay node 7 may be a fixed communications node like a base station 5 or may
itself be a mobile device. Indeed, some mobile telephones 3, 4 may provide relay services and
therefore act as relay nodes. As shown, the relay node 7 includes a transceiver circuit 51 which
is operable to transmit signals to, and to receive signals from, Relay MTs 3-3 to 3-5 and the base
station 5-1 via at least one antenna 53. The operation of the transceiver circuit 5 1 is controlled
by a controller 57 in accordance with software stored in memory 59.
The software includes, among other things, an operating system 61, a communications
control module 63, an MME overload management module 65, an overload message handling
module 67, and a Radio Resource Control (RRC) message handling module 69.
The communications control module 63 is operable to control communication with the
Relay MTs 3-3 to 3-5 and the base station 5-1 including, for example, allocation of resources to
be used by the transceiver circuit 51 in its communications with each of the Relay MTs 3 and
with the base station 5. The communications control module 63 also schedules the times for the
transmission of appropriate sub-frames to relay associated data to the Relay MTs 3-3 to 3-5.
The overload message handling module 67 receives overload messages (both start and
stop messages) forwarded by the donor base station 5-1 and extracts the MME identification
information from the overload messages. The overload message handling module 67 also
extracts any other information required by the MME overload management module 65 to
initiate/terminate the MME overload procedures for the Relay MTs 3-3 to 3-5 (e.g. information
identifying the type of overload actions required).
The MME overload management module 65 initiates MME overload procedures, in
accordance with the required overload actions indicated in associated overload start messages
received from the donor base station 5-1, in respect of the Relay MTs 3-3 to 3-5 served by the
MMEs 9 identified by the MME identification information contained in the overload start
messages. Similarly, the MME overload management module 65 discontinues any MME
overload procedures, in accordance with overload stop messages received from the donor base
station 5-1, in respect of the Relay MTs 3-3 to 3-5 served by the MMEs 9 identified by the MME
identification information contained in the overload stop message.
The RRC message handling module 69 handles RRC messages received from the Relay
MTs 3-3 to 3-5 by interpreting the RRC messages and responding to the messages appropriately.
When an overload procedure has been initiated for an overloaded MME 9, the RRC message
handling module 69 responds to RRC connection establishment messages received from Relay
MTs 3-3 to 3-5, by determining whether or not the message has been received from a mobile
telephone 3 served by the overloaded MME 9. If a message has been received from a mobile
telephone 3 served by the overloaded MME 9, then the RRC message handling module 69
responds by generating a corresponding RRC message to reject or permit the connection attempt
in dependence on the type of overload procedure requested by the overloaded MME 9 and the
reason for the connection establishment message.
Overload Response Initiation Procedure
Figure 4 illustrates, in general terms, a typical procedure followed by key components of
the telecommunication system 1 when an MME 9 experiences an overload situation.
As seen in Figure 4 when the MME 9 experiences an overload situation, it randomly
selects a subset of the base stations that it serves to perform an overload procedure aimed at
alleviating the overload situation (S10). The MME 9 also determines what type of overload
procedure should be performed by the selected base stations. In the example illustrated in Figure
4, a donor base station 5 is selected to perform the overload procedure.
The MME 9 generates an overload start message (SI AP: Overload Start) that includes,
amongst other information, an Overload Action information element which is set by the MME 9
to indicate the type of overload procedure required. This message is then sent to the selected
base stations 5 including the donor base station 5-1 (SI 2).
The type of overload procedure requested by the base station 5 is represented by data in
the Overload Action IE of the overload start message. As described previously, the different
types of overload procedure that a base station 5 may perform comprise:
• Rejection of attempts to establish connections for non-emergency mobile
originated data transfer;
• Rejection of attempts to establish signalling connections; or
• Permitting attempts to establish connections for emergency sessions and mobile
terminated services.
On receipt of the overload start message the donor base station 5-1 determines what type
of overload procedure is required, from the Overload Action IE, and initiates the corresponding
overload procedure accordingly for the Direct MTs 3-1 and 3-2 which the overloaded MME 9
serves (S14). The donor base station 5-1 also modifies the overload start message by inserting
information identifying the MME source of the overload start message into an MME ID
information element in the overload start message and forwards the modified message to the
relay node 7 (SI 6).
On receipt of the overload start message from the donor base station 5-1, the relay node 7
can determine what type of overload procedure is required, from the Overload Action IE and can
determine which MME 9 the overload start message relates to from the MME ID IE. The relay
node 7 initiates the corresponding overload procedure selectively for the Relay MTs 3-3 to 3-5
that the overloaded MME 9 serves (S18).
Overload Response Termination Procedure
Figure 5 illustrates, in general terms, a typical procedure followed by key components of
the telecommunication system 1 when an MME 9, that was previously experiencing an overload
situation, ceases to be overloaded and requires any overload procedures being performed by the
base stations it serves to be discontinued.
As seen in Figure 5, when the MME 9 determines that the overload situation has
terminated (S20), it generates an overload stop message (SI AP: Overload Stop) and sends it to
the base stations 5 performing overload procedures, including the donor base station 5-1 (S22).
On receipt of the overload stop message the donor base station 5-1 stops the
corresponding overload procedure accordingly for the Direct MTs 3-1 and 3-2 which the
overloaded MME 9 serves (S24). The donor base station 5-1 also modifies the overload stop
message by inserting information identifying the MME source of the overload stop message into
an MME ID information element and forwards the modified message to the relay node 7 (S26).
On receipt of the overload stop message from the donor base station 5-1, the relay node 7
determines which MME 9 the overload stop message relates to from the MME ID IE. The relay
node 7 terminates the corresponding overload procedure being performed for the Relay MTs 3-3
to 3-5 which the MME 9 represented by the MME ID IE serves (S28).
Overload Procedure
Figure 6 illustrates, in general terms, an exemplary overload procedure followed by a
relay node 7 of the telecommunication system 1 when a specific overloaded MME 9-1 (MME1
in the illustrated example) has requested the overload procedure.
A Relay MT 3-3 served by the overloaded MME 9-1 attempts to establish a connection
by generating an RRC connection request and sending it to the relay node 7 (S32, S38). The
RRC connection request includes, amongst other information, an establishment cause
information element for identifying what the attempted connection establishment is for. The
establishment cause information element may, for example, be set to any of the following:
• 'mo-data' - to indicate that the attempted connection establishment is for a mobile
originated (mo) data transfer;
• 'mo-signalling' - to indicate that the attempted connection establishment is for
mobile originated (mo) signalling;
• 'mt-Access' - to indicate that the attempted connection establishment is for a
mobile terminated (mt) service;
• 'emergency' - to indicate that the attempted connection establishment is for an
emergency session; or
• 'highPriorityAccess' - to indicate that the attempted connection establishment is
for highPriorityAccess.
The relay node 7 establishes that the Relay MT 3-3 requesting the connection is served
by the overloaded MME 9-1 for which the overload procedure has been initiated. If MT 3-3
requesting the connection is served by the overloaded MME 9-1, then the relay node 7 reads the
establishment cause IE and determines whether it indicates that the RRC connection request
should be rejected or allowed (S34, S39). The relay node 7 then responds to the connection
request by generating and sending an RRC connection reject message (if the connection is to be
rejected - S36) or an RRC connection accept message (if the connection is to be accepted - S40).
The different overload reject/accept actions for the different overload procedures are
summarised below:
• Rejection of attempts to establish connections for non-emergency mobile
originated data transfer reject connection attempt if establishment cause is 'modata',
otherwise permit;
• Rejection of attempts to establish signalling connections reject connection
attempt if establishment cause is 'mo-data' or 'mo-signalling', otherwise permit; or
• Permitting attempts to establish connections for emergency sessions and mobile
terminated services permit connection attempt if establishment cause is
'emergency' or 'mt-access' , otherwise reject.
Thus, only signalling traffic corresponding to permitted RRC connections is sent to the
overloaded MME 9-1.
When rejecting the RRC connection request for overload reasons the relay node 7
indicates, to the affected Relay MT, the cause of the rejection and an appropriate timer value, for
limiting further RRC connection requests within a specified time period.
If the relay node 7 establishes that the Relay MT 3-5 requesting the connection is served
by an MME 9-2 for which an overload procedure has not been initiated then, the relay node 7
then accepts (or rejects) the connection request in accordance with LTE standard procedures
without regard to the overload procedure initiated for the overloaded MME 9-1.
Accordingly, the relay node 7 is advantageously able to perform the actions required in
response to the overload situation being experienced by MME 9-1 for any RelayMT 3-3 served
by MME 9-1 without affecting acceptance or rejection of connection requests received from
Relay MT 3-5 that is being served by MME 9-2, which is not overloaded.
Modifications and Alternatives
A detailed embodiment has been described above. As those skilled in the art will
appreciate, a number of modifications and alternatives can be made to the above embodiment
whilst still benefiting from the inventions embodied therein.
In an alternative embodiment, for example, the donor base station does not forward the
overload start (or overload stop) message to the relay node and, accordingly does not inform the
relay node that a particular MME has become overloaded. Accordingly, in this embodiment, the
relay node 7 will accept an RRC connection request from the Relay MT without regard to any
overload procedure requested by the MME 9 which serves the Relay MT. However, the donor
base station 5 of this embodiment is operable to detect attempts by a Relay MT being served by
an overloaded MME 9 to become active (e.g. to establish communications with another mobile
telephone or communications device in the system), and to prevent or allow the attempt in
dependence on the reason for the attempt, thereby effectively implementing the requested
overload procedure.
In this embodiment, as the skilled person will appreciate, the donor base station 5 is able
to identify the reason for the attempt by the Relay MT (served by the overloaded MME) to
become active from an RRC establishment cause information element contained in a standard SI
AP Initial UE message sent to it by the relay node. The donor base station then determines if the
attempt by the Relay MT to become active should be allowed based on the establishment cause
as described previously. If the donor base station decides that the attempt should not be allowed
(based on the indication given in the overload action IE of the overload start message) it
generates a reply to the S1AP Initial UE message to terminate the connection with the Relay MT
(even though it was accepted by the relay node).
The S1AP Initial UE message is a class 2 procedure and currently a failure message for
replying to the S1AP Initial UE message has not been specified.
A possible reply message that the donor base station may use, to prevent the Relay MT
entering the active state comprises an error indication message, receipt of which causes the relay
node 7 to release the connection with the affected Relay MT using RRC Connection Release.
Whilst an error indication may be used to allow the donor base station 5 selectively to
prevent activation of Relay MTs for overload reasons, it has the following possible issues:
• As mentioned above, the RRC connection will already be established by the time
the relay node sends the Initial UE message. Thus, this solution does not conform
to the principles of the MME overload functionality which, ideally, involves
outright rejection of RRC Connection with an appropriate wait timer. Moreover,
RRC Connection Release does not contain timer information, to allow the period
within which further connection attempts should not be made to be set.
• Ideally, error indication should only be used to report detected errors in an
incoming message rather than to support the overload functionality.
Accordingly, in an embodiment using an error indication in this way, the donor base
station 5 also indicates an associated cause to the relay node 7. On determining that the cause of
the error indication is overload related, the relay node 7 can thus set an appropriate timer value to
limit further RRC connection requests for an associated time period.
Another possible reply message that the donor base station 5 may use, to prevent the
Relay MT entering the active state comprises a UE Context Release message, receipt of which
causes the relay node 7 to release the connection with the affected Relay MT using RRC
Connection Release.
Whilst a UE context release may be used to allow the donor base station 5 to selectively
prevent activation of Relay MTs for overload reasons, it has the following possible issues:
• As with use of an 'error indication', the RRC connection will be already
established by the time the relay node 7 sends the Initial UE message. Thus, this
solution does not conform to the principles of the MME overload functionality
which, ideally, involves outright rejection of RRC Connection with an appropriate
wait timer. Moreover, RRC Connection Release does not contain timer
information, to allow the period within which further connection attempts should
not be made to be set.
• The purpose of the UE Context Release procedure is to enable an MME to order
the release of a UE-associated logical connection due to various reasons. However,
the UE-associated logical connection is not fully established at the time the donor
base station 5 receives the Initial UE message.
In the above embodiments, a mobile telephone based telecommunications system was
described. As those skilled in the art will appreciate, the signalling techniques described in the
present application can be employed in other communications system. Other communications
nodes or devices may include user devices such as, for example, personal digital assistants,
laptop computers, web browsers, etc. As those skilled in the art will appreciate, it is not essential
that the above described relay system be used for mobile communications devices. The system
can be used to extend the coverage of base stations in a network having one or more fixed
computing devices as well as or instead of the mobile communicating devices.
In the above description, the donor base station 5-1 and the relay node 7 are described,
for ease of understanding, as having a number of discrete modules. Whilst these modules may
be provided in this way for certain applications, for example where an existing system has been
modified to implement the invention, in other applications, for example in systems designed with
the inventive features in mind from the outset, these modules may be built into the overall
operating system or code and so these modules may not be discernible as discrete entities.
Where a plurality of MMEs become (or cease to be) overloaded, a list of MME
identifiers may be provided in the associated overload start (or overload stop) message.
Whilst modifying the overload messages to include information identifying the source of
the overload message and forwarding the modified message to the relay node is advantageous in
terms of simplicity, ease of implementation and minimising the number of messages required,
the information identifying the source of the overload message may be sent in any of a number
of different ways. The information may, for example, be sent in a separate message either before
or after the overload message is forwarded. Moreover, instead of modifying and forwarding a
received overload message, a completely new message may be generated which includes the
information identifying the source of the overload message and any information required to
initiate/terminate the associated overload procedures.
While it is beneficial, in terms of ease of implementation, for the base station to insert an
MME's identity into the overload start or stop message, it will be appreciated that an MME
sending overload message may insert its own identity into the overload message prior to sending
it to the selected base stations.
In the embodiments described above, the relay station and the base station will each
include transceiver circuitry. Typically this circuitry will be formed by dedicated hardware
circuits. However, in some embodiments, part of the transceiver circuitry may be implemented
as software run by the corresponding controller.
In the above embodiments, a number of software modules were described. As those
skilled in the art will appreciate, the software modules may be provided in compiled or uncompiled
form and may be supplied to the base station or the relay station as a signal over a
computer network, or on a recording medium. Further, the functionality performed by part or all
of this software may be performed using one or more dedicated hardware circuits.
Various other modifications will be apparent to those skilled in the art and will not be described
in further detail here.
The following is a detailed description of the way in which the present inventions may be
implemented in the currently proposed 3GPP standard. Whilst various features are described as
being essential or necessary, this may only be the case for the proposed 3GPP standard, for
example due to other requirements imposed by the standard. These statements should not,
therefore, be construed as limiting the present invention in any way.
1 Introduction
The objective of the paper is to analyse how the MME Overload function works in an RN
deployment scenario. The paper highlights related issues and analyse different solution (e.g.
MME Overloading terminating to DeNB or RN). Also the paper highlights pros and cons of the
different solution and it propose a way forward accordingly.
2 Background
MME Overload
The MME Overload procedure was introduced to control overload situation in MME.
When MME experience an overload situation, it will randomly choose some eNBs towards
which the MME Overload procedure is sent. The MME will indicate to the eNB which action
should eNB undertake upon overload indication.
Depending on the Overload Action IE in SIAP overload start, eNB shall
- "reject all RRC connection establishments for non-emergency mobile originated data
transfer" (i.e. reject traffic corresponding to RRC cause "mo-data"), or
- "reject all RRC connection establishments for signalling" (i.e. reject traffic
corresponding to RRC cause "mo-data" and "mo-signalling"), or
- "only permit RRC connection establishments for emergency sessions and mobile
terminated services" (i.e. only permit traffic corresponding to RRC cause
"emergency" and "mt-Access").
When rejecting an RRC connection request for overload reasons the eNB indicates to the
UE an appropriate timer value that limits further RRC connection requests for a while [1].
MME pool and RN deployment
According to the agreed Relay architecture, DeNB will be seen as an MME from RN
view. As a consequence RN will not have any knowledge on which MME has triggered a
certain non UE associated procedure.
3 Discussion
In figure 7, RN is serving UE1 and UE2: UE1 is being served by MME1 and UE2 is
being served by MME2. Assuming MME1 will get overloaded, it will send an Overload
message to DeNB. DeNB need to take action upon reception of SIAP Overload start e.g. reject
the RRC connection with establishment cause as indicated by the MME.
During the overload situation, the affected UEs being served by the RN need to be
handled as well. Different solutions are discussed below:
DeNB does not inform the RN that a certain MME is overloaded. This means that it
is up to the DeNB to reject any UE attempt to go to active state if the UE is being
served by the overloaded MME and the cause for going to active is in line with the
indication given by the overloaded MME. The DeNB will be aware about the
reason of the RRC connection establishment request from the RRC Establishment
cause IE in S1AP Initial UE message. However, the S1AP Initial UE message is a
class 2 procedure and a failure message is not specified. Two possible reply are
considered below.
Error Indication
• Problem in using Error indication
o The RRC connection will be already established by the
time the RN sends the Initial UE message. Thus this
solution is not in line with the principles of the MME
Overload functionality which foresee the rejection of
RRC Connection with an appropriate wait timer. RRC
Connection Release does not contain the wait timer
information.
o Error indication should only be used when to report
detected errors in one incoming message and not as
support to CP functionality e.g. Overload function
o If it will be decided to go for Error Indication, text
procedure would be needed to clarify that the DeNB
need to indicate appropriate cause so that RN can an
appropriate timer value that limits further RRC
connection requests for a while.
■ UE Context Release
• Problems in using UE Context Release
o The RRC connection will be already established by the
time the RN send the Initial UE message (same
problem as for the error indication). Thus this solution
is not in line with the principles of the MME Overload
functionality which foresee the rejection of RRC
Connection with an appropriate wait timer. RRC
Connection Release does not contain the wait timer
information.
o The purpose of the UE Context Release procedure is to
enable the MME to order the release of the UEassociated
logical connection due to various reasons.
However the UE associated logical connection is not
yet established at the time DeNB receives the Initial Ue
message [2].
DeNB forward the Overload message to the RN
o Possible problem
■ the RN does not know which MME is currently overloaded and it may
end up rejecting unnecessarily all attempted RRC Connections
establishment e.g. it may end up reject RRC Connection establishment
from both UEl and UE2 when actually just MME2 is overloaded
(figure2).
o Solution
■ In order to overcome this issue, the DeNB should indicate to the RN
which MME is overloaded when forwarding the S1AP overload start
and Overload stop. This information may also be useful in case e.g.
two MME gets overloaded (via allowing parallel procedure in Uu or
list of MME id in the S1AP Overload messages)
Proposals:
It is proposed that the overload messages are forwarded by the DeNB to the RN
It is proposed to add a new optional IE In S1AP overload related messages so that
RN is able to identify the affected RRC connection request.
4 Conclusion
This paper has analysed issues related to the MME Overload function in case of RN
deployment. It is proposed to discuss the paper and agree on the proposal in chapter 3.
5 Reference
[1] 23.401: General Packet Radio Service (GPRS) enhancements for Evolved
Universal Terrestrial Radio Access Network (E-UTRAN) access
[2] 36.401 : Evolved Universal Terrestrial Radio Access Network (E-UTRAN);
Architecture description
This application is based upon and claims the benefit of priority from United Kingdi
patent application No. 1013559.8, filed on August 12, 2010, the disclosure of which is
incorporated herein in its entirety by reference.
WO 2012/020850 PCT/JP2011/068718
CLAIMS
1. A relay node for a communication system comprising a plurality of mobility
management entities (MMEs), the relay node comprising:
means for associating a plurality of mobile devices with the relay node wherein each
mobile device is served by an MME of said plurality of MMEs;
means for receiving, from a base station, a request that an overload action be performed
and identity information representing an identity of an MME that requested the overload action;
and
means for selectively performing said requested overload action in respect of the mobile
devices associated with the relay node in dependence on the identity information representing an
identity of an MME that requested the overload action.
2. A relay node as claimed in claim 1 wherein the requested overload action
comprises initiating an overload procedure.
3. A relay node as claimed in claim 2 wherein the overload procedure comprises:
receiving a request to establish a connection from a mobile telephone associated with the
relay node;
determining whether or not the mobile telephone that made the request is served by the
MME having the identity represented by the identity information;
generating a message for rejecting said request to establish a connection or generating a
message for accepting said request to establish a connection in dependence on whether or not the
mobile telephone that made the request is served by the MME having the identity represented by
the identity information; and
transmitting said generated message to the mobile telephone that made the request to
establish a connection.
4. A relay node as claimed in claim 3 wherein the overload procedure initiated by
the performing means further comprises determining a reason for the requested connection
establishment request, and wherein said generation step further comprises generating said
message for rejecting said request to establish a connection or generating said message for
accepting said request to establish a connection in dependence on said determined reason for the
requested connection.
5. A relay node as claimed in claim 1 wherein the requested overload action
comprises terminating an overload procedure.
6. A base station for a communication system comprising a plurality of mobility
WO 2012/020850 PCT/JP2011/068718
management entities (MMEs), the base station comprising:
means for receiving, from an MME, a request that an overload action be performed;
means for generating identity information representing an identity of the MME that
requested the overload action; and
means for transmitting, to a relay node, the request that the overload action be performed
and the information representing an identity of the MME that requested the overload action.
7. A base station as claimed in claim 6 further comprising means for inserting said
information representing an identity of the MME that requested the overload action into said
request that the overload action be performed, whereby said information representing an identity
of the MME that requested the overload action is transmitted as part of said request that the
overload action be performed.
8. A base station as claimed in claim 6 or 7 wherein said request that the overload
action be performed comprises a request for an overload procedure to be initiated.
9. A base station as claimed in claim 6 or 7 wherein said request that the overload
action be performed comprises a request for an overload procedure to be terminated.
10. A method performed by a relay node in a communication system comprising a
plurality of mobility management entities (MMEs), the method comprising:
associating a plurality of mobile devices with the relay node wherein each mobile device
is served by an MME of said plurality of MMEs;
receiving, from a base station, a request that an overload action be performed and identity
information representing an identity of an MME that requested the overload action; and
selectively performing said requested overload action in respect of the mobile devices
associated with the relay node in dependence on the identity information representing an identity
of an MME that requested the overload action.
11. A method performed by a base station in a communication system comprising a
plurality of mobility management entities (MMEs), the method comprising:
receiving, from an MME, a request that an overload action be performed;
generating identity information representing an identity of the MME that requested the
overload action; and
transmitting, to a relay node, the request that the overload action be performed and the
information representing an identity of the MME that requested the overload action.
12. A communications device for a communication system that comprises a plurality
of mobility management entities (MMEs), a base station, a relay node, and a plurality of mobile
devices associated with the relay node the communications device comprising:
WO 2012/020850 PCT/JP2011/068718
means for receiving a request that an overload action be performed for at least one of said
plurality of MMEs and identity information representing an identity of an MME that requested
the overload action; and
means for selectively performing said requested overload action in respect of the mobile
devices associated with the relay node in dependence on the identity information representing an
identity of an MME that requested the overload action.
13. A communications device as claimed in claim 12 wherein said communications
device is said relay node.
14. A communications device as claimed in claim 13 wherein the requested overload
action comprises initiating an overload procedure, and wherein said overload procedure
comprises:
receiving a request to establish a connection from a mobile telephone associated with the
relay node;
determining whether or not the mobile telephone that made the request is served by the
MME for which the overload action was requested;
generating a message for rejecting said request to establish a connection or generating a
message for accepting said request to establish a connection in dependence on whether or not the
mobile telephone that made the request is served by the MME for which the overload action was
requested; and
transmitting said generated message to the mobile telephone that made the request to
establish a connection.
15. A communications device as claimed in claim 12 wherein said communications
device is said base station.
16. A communications device as claimed in claim 15 wherein the requested overload
action comprises initiating an overload procedure, and wherein said overload procedure
comprises:
receiving an indication that a connection has been established between a mobile
telephone associated with the relay node and the relay node;
determining whether or not the mobile telephone for which the connection is established
is served by the MME for which the overload action has been requested;
selectively generating a message for terminating said established connection in
dependence on whether or not the mobile telephone for which the connection is established is
served by the MME for which the overload action has been requested; and
transmitting any message so generated to the relay node.
WO 2012/020850 PCT/JP2011/068718
17. A communications device as claimed in claim 6 wherein the message for
terminating said established connection comprises an error indication.
18. A communications device as claimed in claim 16 wherein the message for
terminating said established connection comprises a message for releasing a context of the
mobile telephone.
19. A method performed by a communications device in a communication system
that comprises a plurality of mobility management entities (MMEs), a base station, a relay node,
and a plurality of mobile devices associated with the relay node, the method comprising:
receiving a request that an overload action be performed for at least one of said plurality
of MMEs and identity information representing an identity of an MME that requested the
overload action; and
selectively performing said requested overload action in respect of the mobile devices
associated with the relay node in dependence on the identity information representing an identity
of an MME that requested the overload action.
20. A communication node for a communication system comprising a plurality of
mobility management entities (MMEs), the communication node comprising:
means for associating a plurality of mobile devices with the communication node
wherein each mobile device is served by an MME of said plurality of MMEs;
means for receiving, from a further communication node, a request that an overload
action be performed and identity information representing an identity of an MME that requested
the overload action; and
means for selectively performing said requested overload action in respect of the mobile
devices associated with said communication node in dependence on the identity information
representing an identity of an MME that requested the overload action.
2 1. A communication node for a communication system comprising a plurality of
mobility management entities (MMEs), the base station comprising:
means for receiving, from an MME, a request that an overload action be performed;
means for generating identity information representing an identity of the MME that
requested the overload action; and
means for transmitting, to a further communication node, the request that the overload
action be performed and the information representing an identity of the MME that requested the
overload action.
22. A method performed by a communication node in a communication system
comprising a plurality of mobility management entities (MMEs), the method comprising:
WO 2012/020850 PCT/JP2011/068718
associating a plurality of mobile devices with the communication node wherein each
mobile device is served by an MME of said plurality of MMEs;
receiving, from a further communication node, a request that an overload action be
performed and identity information representing an identity of an MME that requested the
overload action; and
selectively performing said requested overload action in respect of the mobile devices
associated with said communication node in dependence on the identity information representing
an identity of an MME that requested the overload action.
23. A method performed by a communication node in a communication system
comprising a plurality of mobility management entities (MMEs), the method comprising:
receiving, from an MME, a request that an overload action be performed;
generating identity information representing an identity of the MME that requested the
overload action; and
transmitting, to a further communication node, the request that the overload action be
performed and the information representing an identity of the MME that requested the overload
action.
24. A computer program product comprising computer implementable instructions
for causing a programmable computer device to become configured as the relay node of any of
claims 1 to 5, as the base station of any of claims 6 to 9, as the communications device of any of
claims 12 to 18, or as a communication node according to claim 20 or 21.