2. The conlmunication relay apparatus according to Claim 1; wherein the second transmission control c i r c u i t n o t i f i e s the first transmission control c i r c u i t of existence or absence of a f a u l t in the 10 second board, when the operation state of the f i r s t board is t h e a c t i v e system and the first transmission control c i r c u i t detects a f a u l t in the first board, the f i r s t transmission control c i r c u i t evaluates a s t o whether or not the usage of the f i r s t transmission path i s allowed according to existence or absence 15 of a f a u l t in the second board, and the first transmission control c i r c u i t gives an instruction to the IF unit based on an evaluation r e s u l t .

3. The communication relay apparatus according to Claim 2, 20 wherein when t h e operation s t a t e of the f i r s t board is switched, the first communication state control unit determines a switch pattern f o r t h e first transmission c i r c u i t to switch between whether o r not the usage of the , first transmission p,ath i s allowed based on the switched operation state 25 and sets the determined switch pattern in the f i r s t transmission control circuit, when the f i r s t transmission control c i r c u i t detects a f a u l t in the first board o r receives, from the second transmission control c i r c u i t , a notification t h a t a f a u l t i s detected, the first transmission control c i r c u i t 30 i d e n t i f i e s whether o r not the usage of the f i r s t transmission path i s allowed according to the switch pattern t h a t has been set by the first col~tmunications tate control u n i t and a combination of existence o r absence of a fault i n t h e first board and existence or absence of a f a u l t in the second board, which i s notified by t h e second transmission control circuit, and the first transmission control c i r c u i t givcs an instruction of a rcsult of the identification to the IF unit.

4. The communication relay apparatus according to any one of Claims 1 to 3, wherein when the f i r s t con~munication state control u n i t detects a fault, which cannot be detected by the first transnlission control c i r c u i t , in the first board, the first c o n ~ n ~ u n i c a t i osnta te control unit n o t i f i e s the first 10 translnission control c i r c u i t that the f a u l t i s detected in the f i r s t board, and when the f i r s t transmission control c i r c u i t receives a notification from the f i r s t communication state control u n i t , the first transmission control c i r c u i t detects the f a u l t as a fault in the first board. 15

5. The communication relay apparatus according to any one of Claims 1 to 4, wherein in response to the notification from the first transmission control c i r c u i t , the second transmission control c i r c u i t further n o t i f i e s the second 20 communication state control unit that the first board is faulty, in response to a notification from the second transmission control c i r c u i t , the second communication s t a t e control unit changes an operation state of the second board to a s t a t e not allowed to be switched and . notifies the f i r s t communication state control u n i t to t h a t e f f e c t , 2 5 in response to a notification from the second comn~unication state control u n i t , the first conln~unication state control unit transfers the communication state of the communication d a t a , which has passed through the f i r s t transmission path, to the second communication s t a t e control unit, and 3 0 a f t e r the second co~nmunication state control unit c o n ~ p l e t e s setting of the communication s t a t e , which has been transferred from the first comnlunication state control u n i t , the second communication s t a t e control unit switches the operation state of the second board to the active system. 6 . A nletltod of switching an active system using a con~munication relay apparatus that comprises: an IF unit that externally transmits and receives communication 5 data; a first board that comprises: a first transmission control circuit that i s connected to the IF unit by a first transmission path and controls usage of the f i r s t transmission path by the IF unit; and 10 a first communication state control unit t h a t manages a con~munication state of the communication data t h a t has passed through the f i r s t transmission path; and a second board t h a t i s mounted as a redundant f i r s t board and comprises: 15 a second transmission control c i r c u i t that is connected to the IF unit by a second transmission path and controls usage of the second transmission path by the IF unit; and a second communication state control unit t h a t manages a communication s t a t e of the communication data t h a t has passed through 20 the second transmission path, the method comprising: when an operation state of the first board is an active system and the first transmission control c i r c u i t detects a f a u l t in t h e f i r s t board, by the f i r s t transmission control c i r c u i t , giving an instruction to the IF unit a s t o whether o r not t h e usage of t h e f i r s t transmission path is allowed 25 and notifying the second transmission control c i r c u i t and the f i r s t communication state control u n i t t h a t the f a u l t i s detected, in response to a notification from the first translnission control circuit, by the second transmission control c i r c u i t , giving an instruction to the IF unit a s t o whether o r not the usage of the second transmission 30 path i s allowed, by the f i r s t communication slate control unit, evaluating as to whether o r not to switch the operation state of the first board to a standby system, and when an evaluation i s made to switch the operation state of the first board to the standby system, by the f i r s t communication s t a t e c o n t r o l unit, starting to takc over the communication state of the communication data that has passed through the f i r s t transmission path.

7. The method according to Claim 6 , wherein the second transmission control c i r c u i t n o t i f i e s the f i r s t transmission control c i r c u i t of existence o r absence of a f a u l t in the second board, when the operation state of the f i r s t board i s the active system and 10 the first transmission control c i r c u i t detects a f a u l t in the f i r s t board, the f i r s t transmission control c i r c u i t evaluates a s t o whether or not the usage of the first transmission path i s allowed according to existence or absence of a f a u l t in the second board, and the first transmission control c i r c u i t gives an instruction to the IF 15 unit based on an evaluation r e s u l t .

8. The method according to Claim 7, wherein: when the operation state of the first board i s switched, t h e f i r s t communication state control u n i t determines a switch pattern for the first 20 transmission c i r c u i t to switch between whether o r not the usage of the f i r s t transmission path i s allowed based on the switched operation state and sets the determined switch pattern in the f i r s t transmission control circuit, when the f i r s t transmission c o ~ l t r o l circuit detects a f a u l t in the 25 first board o r receives, from the second transmission control c i r c u i t , a notification t h a t a f a u l t is detected, the f i r s t transmission control c i r c u i t i d e n t i f i e s whether o r not the usage of the f i r s t transmission path i s allowed according to the switch pattern that has been set by the f i r s t communication state control unit and a combination of existence o r 30 absence of a f a u l t in the first board and existence o r absence of a f a u l t in the second board, and the first transmission control c i r c u i t gives an instruction of a result of the identification to the IF unit.

9. The method according to any one of Claims 6 to 8, wherein when the first communication state control tinit detects a f a u l t , which cannot be detected by the f i r s t transmission control c i r c u i t , in the first board, the first communication state control unit n o t i f i e s the f i r s t 5 transmission control c i r c u i t that the fault is detected in the f i r s t board, and when the first transmission control c i r c u i t receives a notification from the first communication s t a t e control unit, the first transmission control circuit detects ihe fault as a f a u l t in the f i r s t board. 10

10. The method according to any one of Claims 6 to 9, wherein in response to the notification from the first transmission control c i r c u i t , the second transmission control c i r c u i t further n o t i f i e s the second communication state control unit t h a t t h e f i r s t board is faulty, 15 in response to a notification from the second transmission control c i r c u i t , the second communication state control unit changes an operation state of the second board to a state not allowed to be switched and n o t i f i e s the f i r s t communication state control u n i t to t h a t e f f e c t , in response to a notification from the second communication state 20 control unit, the first communication state control unit t r a n s f e r s t h e communication state of the communication d a t a , which has passed through the f i r s t transmission path, to the second communication state control unit, and . a f t e r the second co,mmunication state control u n i t completes 25 setting of the communication state, which has been transferred from the first communication s t a t e c o n t r o l unit, the second communication state control u n i t switches the operation state of the second board to the active system. 3 0 11. A co.n~municationr elay control board comprising: a f i r s t transmission control c i r c u i t that i s connected to an IF unit by a f i r s t transmission path and controls usage of the first transnlission path by the IF unit, the IF unit externally transmitting and receiving communication data; and a first comnlunication s t a t e control unit that manages a control state of the colnmunication data that has passed through the f i r s t transmission path, wherein the communication relay control board is mounted as a redundant 5 board of another board that is connected to the IF unit by a second transmission path, when an operation state of the first transmission control c i r c u i t i s an active system and detects i t s own f a u l t , the f i r s t transmission control circuit 10 gives an instruction to the IF unit as to whether or not the usage of the first transmission path i s allowed, notifies the other board that the f a u l t i s detected and gives an instruction to the IF unit whether o r not usage of the second transmission path i s allowed, and 15 n o t i f i e s the first communication state control u n i t t h a t the fault is detected, in response to a notification from the first transmission control circuit, the f i r s t communication state control unit evaluates a s t o whether or not to switch i t s own operation state to a standby system, and 2 0 when the first communication state control u n i t evaluates t h a t its own operation state i s switched to the standby system, the first communication s t a t e control u n i t starts to take over the communication state of the comnlunication d a t a , which has passed through t h e f i r s t trans'mission path, to the other board. 2 5

12. The communication relay control board according to Claim 11, wherein when the operation state of the f i r s t board i s the active system and the first transmission control c i r c u i t d e t e c t s a fault in the first board, the 30 first t r a n s n ~ i s s i o nc ontrol c i r c u i t evaluates as to whether or not the usage of the f i r s t transmission path i s allowed according to existence o r absence of a fault in the second board, and the f i r s t transmission control circuit gives an instruction to the IF unit based on an evaluation result.

13. The c o m ~ n u n i c a t i ore~l~a y control board according to Claim 12, wherein when the operation state of the first board i s switched, the f i r s t 5 communication state control unit determines a switch pattern f o r t h e first transmission c i r c u i t to switch between whether o r not the usage of the f i r s t transmission path i s allowed based on the switched operation slate and sets the determined switch pattern in the f i r s t transmission control circuit, 10 when the f i r s t transmission control c i r c u i t detects a fault in the first board or receives, from the second transmission control c i r c u i t , a notification t h a t a f a u l t i s detected, the f i r s t transmission control c i r c u i t i d e n t i f i e s whether or not the usage of the f i r s t transmission path is allowed according to the switch pattern t h a t has been set by the first 15 communication s t a t e control unit and a combination of existence or absence of a fault in the f i r s t board and existence o r absence of a fault in the second board, which is notified by the second board, and the f i r s t transmission control c i r c u i t gives an instruction of a result of the identification to the IF unit. 2 0

14. The communication relay control board according to any one of Claims 11 to 13, wherein when the f i r s t communication state control unit detects a fault, which.cannot be detected by.the first transmission control c i r c u i t , in the 25 f i r s t board, the f i r s t com~nunication state control unit n o t i f i e s the f i r s t transmission control c i r c u i t t h a t the f a u l t i s detected in the f i r s t board, and when the f i r s t transmission control c i r c u i t receives a notification from the f i r s t comnlunication state control u n i t , the first transmissioll 30 control c i r c u i t detects the fault as a fault in the f i r s t board.

DESCRIPTION
COMMUNICATION RELAY APPARATUS, ACTIVE SYSTEM
SWITCIIING METHOD, AND COMMlJNICATION RELAY CONTROL
BOARD
Technical Field
[OOOl]
The present invention relates to a comn~unicationr elay apparatus,
an active system switching method, and a communication relay control
10 board, and particularly to a communication relay apparatus including a
plurality of control boards mounted therein in a redundant manner, an
active system switching method, and a communication relay control
board.
15 Background Art
[0002]
'' Patent Literature 1 d i s c l o s e s a technique concerning a redundant
system including l i n e s composed of a SONETISDH (Synchronous Optical
NETworkISynchronous Digital Hierarchy) network. In the redundant
20 system of Patent Literature 1, the f a u l t detection unit of the INF on the
reception side monitors a fault in the respective paths in lines on the
reception side and notifies the switch evaluation unit of a result of
monitoring. Then, the switch evaluation unit selects a path according to
a notification and notifies the INF on the transmission s i d e .
2 5
Citation List
Patent Literature
[0003]
Patent Literature 1 : Japanese Unexamined Patent Application Publication
30 No. 2004-328687
Summary of Invention
Technical Problem
[0004]
As there i s one switch evaluation unit per communication relay
apparatus in Patent Literature 1, Patent Literature 1 has room for
improvement, which i s to provide redundant switching evaluation units.
In recent years, there is a need for a wired o r wireless communication
5 relay apparatus to support not only the time-division n~ultiplexing but
also the all-packet network.
[0005]
However, in the communication relay apparatus as in Patent
Literature 1, there has been a problem that it i s d i f f i c u l t to provide
10 redundant control units inside the apparatus while satisfying the above
need.
[0006]
In general, switching the communication in the time-division
multiplexing is often targeted to be completed within 50 ms. Thus, it
15 might be possible to use a board that i s composed by integrating a TDM
(Time Division Multiplexing) switching c i r c u i t (hereinafter referred to as
a "TDMSW") and a hardware c i r c u i t for monitoring a fault and to switch
the TDMSW in case of a fault. By providing a redundant board of such a
board and when a f a u l t occurs in one of the TDMSWs and switching to the
20 other TDMSW using the above-mentioned hardware c i r c u i t , i t would be
possible to achieve switching within 50 ms.
[0007]
However, as switching in the all-packet network requires takeover
of a communication s t a t u s and a protocol, it is necessary to switch the
25 control device, such as CPUs (Central Processing Unit). There are
various cases of the communication status and protocol in case of a fault,
and thus information to be taken over differs from case to case.
Therefore, such takeover cannot be performed by only the
above-mentioned hardware c i r c u i t dedicated for switching, thereby
30 disabling the comn~unication a f t e r the switching or making the
comn~unication state inaccurate. Accordingly, it is not possible to
achieve switching in the all-packet network by only providing redundant
hardware c i r c u i t s dedicated for switching. On the contrary, by simply
providing redundant CI'Us and switching them by only the CPUs, it takes
time t o s w i t c h the c o n ~ ~ n u n i c a t i oinn t h e t i m e - d i v i s i o n multiplexing,
thereby not a c h i e v i n g t h e s w i t c h i n g within 50 ms.
[OOOS]
'The p r e s e n t i n v e n t i o n i s made t o s o l v e s u c h a problem and aims to
5 provide a communication r e l a y a p p a r a t u s , an active systetn switching
method, and a communication r e l a y c o n t r o l board t h a t r e a l i z e a c c u r a t e
takeover of the colnmunication state while maintaining t h e s p e e d of
switching in t h e s w i t c h i n g c o n t r o l by t h e communication relay apparatus
t h a t p e r f o r m s a communication r e l a y i n the time-division multiplexing
10 and the all-packet network.
Solution to Problem
[0009]
According t o a f i r s t exemplary a s p e c t of t h e p r e s e n t i n v e n t i o n , a
15 communication relay apparatus includes:
an I F u n i t t h a t e x t e r n a l l y t r a n s m i t s and r e c e i v e s communication
data;
a f i r s t board t h a t i n c l u d e s :
a f i r s t transmission c o n t r o l c i r c u i t t h a t is c o n n e c t e d t o the
20 IF unit by a f i r s t t r a n s m i s s i o n path and controls usage of t h e f i r s t
t r a n s m i s s i o n p a t h by the IF u n i t ; and
a f i r s t communication s t a t e c o n t r o l u n i t t h a t manages a
conlmunication state of the comnlunication d a t a t h a t has passed through
t h e f i r s t t r a n s m i s s i o n p a t h ; and
2 5 a second board that i s mounted a s a redundant board of t h e f i r s t
board and comprises:
a second t r a n s m i s s i o n c o n t r o l c i r c u i t t h a t is c o n n e c t e d t o t h e
IF unit by a s e c o n d t r a n s m i s s i o n p a t h and c o n t r o l s u s a g e of the second
t r a n s m i s s i o n p a t h by the I F u n i t ; and
3 0 a second c o n ~ m u n i c a t i o n s t a t e c o n t r o l u n i t that manages a
communication s t a t e of the communication d a t a t h a t has passed through
the s e c o n d t r a n s m i s s i o n p a t h , in which
when an operation s t a t e o f t h e f i r s t board is an active systern and
t h e f i r s t t r a n s m i s s i o n c o n t r o l c i r c u i t d e t e c t s a fault in the f i r s t board, the
first trans~nission control c i r c u i t gives an instruction to the IF unit as to
whethcr or not the usage of the f i r s t transtnission path is allowed and
notifies the second transnlission control circuit and the f i r s t
comn~unication statc control unit t h a t the f a u l t i s detected,
5 in response to a notification from the f i r s t transmission control
c i r c u i t , the second transnlission control c i r c u i t gives an instruction to the
IF unit a s t o whether o r not the usage of the second transmission path is
allowed,
the f i r s t communication state control unit evaluates a s t o whether
10 or not to switch t h e operation state of the first board to a standby system,
and
when an evaluation i s made to switch the operation state of the
first board to the standby system, the f i r s t communication state control
unit starts to take over the communication state of the communication
15 data, which has passed through the f i r s t transmission path, to the second
communication stale control unit.
[OO l o ]
According to a second exemplary aspect of the present invention, a
20 method of switching an active system using a communication relay
apparatus that includes:
an IF u n i t t h a t externally transmits and receives communication
data;
a.first board that includes:
2 5 a f i r s t transmission control c i r c u i t that i s connected to the
IF unit by a f i r s t transmission path and controls usage of the first
transmission path by the IF unit; and
a f i r s t communication state control unit that manages a
conlmunication state of the communication data t h a t has passed through
30 the f i r s t transnlission path; and
a second board that is mounted as a redundant first board and
comprises:
a second transmission control c i r c u i t t h a t i s connected to the
IF unit by a second transmission path and controls usage of the second
transinission path by the IF unit; and
a second c o m ~ ~ ~ u n i c a tsitoante control unit that nlanages a
communication state of the communication data t h a t has passed through
the second transn~ission path, the method including:
5 when an operation s t a t e of the first board is an active system and
the first transmission control c i r c u i t detects a fault in the f i r s t board, by
the first transmission control c i r c u i t , giving an instruction to the IF unit
a s t o whether or not the usage of the f i r s t transmission path i s allowed
and notifying the second transmission control c i r c u i t and the first
10 conlmunication s t a t e control unit that the f a u l t i s detected,
in response to a notification from the first transmission control
circuit, by the second transmission control c i r c u i t , giving an instruction
to the IF unit as to whether o r not the usage of the second transmission
path i s allowed,
15 by the f i r s t communication state control u n i t , evaluating as to
whether o r not to switch t h e operation state of the first board to a standby
system, and
when an evaluation i s made to switch the operation state of the
first board to the standby system, by the f i r s t communication state control
20 u n i t , s t a r t i n g to take over the communication state of the communication
data t h a t has passed through the f i r s t transmission path.
[00111
According to a t h i r d exemplary aspect of the present invention, a
communication relay control board includes:
2 5 a first transmission control c i r c u i t t h a t is connected to an IF unit,
which externally transmits and receives communication d a t a , by a first
transmission path and controls usage of the f i r s t transmission path by the
IF unit; and
a first comn~unications tate control unit that manages a control
30 state of the communication data that has passed through the f i r s t
transmission path, in which
the communication relay control board is mounted as a redundant
board of another board t h a t i s connectcd to the IF unit by a second
transmission path,
when an operation s t a t e of the f i r s t transmission control c i r c u i t i s
an active system and detects i t s own f a u l t , the first transmission control
circuit
gives an instruction to the IF unit as to whether o r not the
usage of the f i r s t transmission path i s allowed,
notifies the other board that the f a u l t i s detected and gives
an instruction to the IF unit whether or not usage of the second
transmission path i s allowed, and
notifies the f i r s t communication state control unit that the
10 f a u l t i s detected,
in response to a notification from the first transmission control
c i r c u i t , the f i r s t communication s t a t e control unit evaluates as to whether
or not to switch i t s own operation state to a standby system, and
when the first communication state control u n i t evaluates that its
15 own operation state i s switched to the standby system, the f i r s t
communication s t a t e control u n i t starts to take over the communication
state of the communication d a t a , which has passed through the first
transmission path, to the other board.
20 Advantageous E f f e c t s of Invention
[OO 121
According to the present invention, it is possible to provide a
communication relay apparatus, an active system switching method, and a
communica~ionr elay control board that realize accurate takeover of the
25 communication s t a t e while maintaining the speed of switching in
switching control by the communication relay apparatus t h a t performs a
communication relay in the time-division multiplexing and the all-packet
network.
30 Brief Description o f Drawings
100131
Fig. 1 is a block diagram showing a configuration of a
communication relay apparatus according to a f i r s t exemplary
embodiment of the present invention;
Fig. 2 is a sequence diagram showing a flow of active system
switching processing upon detection of a f a u l t according to the first
exemplary embodiment of the present invention;
Fig. 3 is a block diagram schematically showing a con~munication
5 relay apparatus according to a second exemplary embodiment of the
present invention;
Fig. 4 is a block diagram showing main components of the
communication relay apparatus according to the second exemplary
embodiment of the present invention;
10 Fig. 5 is a diagram showing an example of operation states of a
device control card according to the second exemplary embodiment of the
present invention;
Fig. 6 is a block diagram showing main components of the device
control card according to the second exemplary embodiment of the
15 present invention;
Fig. 7 is a diagram showing an example of an evaluation r u l e o f a n
ACT signal according to the second exemplary embodiment of the present
invention;
Fig. 8 is a diagram showing an example of a correspondence
20 relation between the operation s t a t e s and ACT operation patterns
according to the second exemplary embodiment of the present invention;
Fig. 9 is a sequence diagram showing a flow of an active system
switching process upon defection of a f a u l t according to the second
exemplary embodiment of the present invention;
2 5 Fig. 10 is a flowchart showing a flow of f a u l t analysis processing
according to the second exemplary embodiment of the present invention;
Fig. 11 is a diagram showing an example (116) of t h e a c t i v e system
switching operation upon detection of a f a u l t according to the second
exemplary embodiment of the present invention;
3 0 Fig. 12 is a diagram showing the example (216) of the active system
switching operation upon detection of a f a u l t according to the second
exemplary embodiment of the present invention;
Fig. 13 is a diagram showing the example (316) of the active system
switching operation upon detection of a f a u l t according to the second
exemplary elilbodilnent of the present invention;
Fig. 14 is a diagram showing the example (416) of the active system
switching operation upon detection of a f a u l t according to the second
exemplary embodiment of the present invention;
5 Fig. 15 is a diagram showing the example (516) of the active system
switching operation upon detection of a f a u l t according to the second
exemplary embodiment of the present invention; and
Fig. 16 is a diagram showing the example (616) of the active system
switching operation upon detection of a f a u l t according to the second
10 exemplary embodiment of the present invention.
Description of Embodiments
[00 141
Hereinafter, specific embodiments incorporating the present
15 invention s h a l l be explained in d e t a i l with reference to the drawings.
The same components are denoted by the same reference numerals
throughout the drawings, and a repeated explanation s h a l l be omitted as
necessary f o r c l a r i t y of the explanation.
[00 151
20
Fig. 1 i s a block diagram showing a configuration of a
communication relay apparatus 1 according to a f i r s t exemplary
embodiment of the present invention. The communication relay
apparatus 1 is.an apparatus that relays communication data 14 that is
25 exchanged among a plurality of external communication base stations and
colnmunication terminals. The comn~unicationr elay apparatus 1 may be,
for example, a microwave communication system (e.g., a communication
system apparatus that links mobile phone base stations). Note that
lilicrowave comlnunication systems often support optical microwave
30 communication, wireless comniunication and the l i k e .
[00 161
The con~municationre lay apparatus 1 includes a t l e a s t an IF unit 10,
a first board 11, and a second board 12. Note that the communication
relay apparatus 1 has other components necessary for relaying the
communication in addition to the ones stated above. However, as those
components are con~monly-knownc omponents, an illustration and
explanation thereof s h a l l be omitted.
LOO 171
5 The IF unit 10 externally transmits and receives the communication
data 14. The comn~unicationd ata 14 is data exchanged among a plurality
of external communication base stations and communication terminals.
The f i r s t board 11 is a board connected to the IF unit 10 by a first
transmission path 131. Moreover, the second board 12 is a board
10 connected to the IF unit 10 by a second transmission path 132. Both the
f i r s t transmission path 131 and the second transmission path 132 are
buses for transmitting the communication data 14.
[OO 181
Each of the first board 11 and the second board 12 is a control
15 board h.aving a function to independently control relay processing of the
communication data 14 in the communication relay apparatus 1. Further,
the first board 11 and the second board 12 are mounted i n t h e
communication relay apparatus 1 in a redundant manner. Normally, an
operation state of one of the boards i s an active system, and an operation
20 slate of the other board is a standby system. Moreover, the number of
control boards mounted i n t h e communication relay apparatus 1 i s not
limited to two and may be t h r e e or more.
[00 191
7. The first.board 11 includes a f i r s t transmission control c i r c u i t 11 1
25 and a f i r s t communication s t a t e control unit 112. The first transmission
control c i r c u i t 111 is a semiconductor integrated c i r c u i t t h a t controls
usagc of the f i r s t transmission path 131 by the IF unit 10. The first
transillission control c i r c u i t 11 1 can be implemented by, for example,
FPGA (Field Programmable Gate Array). Moreover, thc first
30 transmission control c i r c u i t 11 1 controls, for example, cross connections
and switching of paths in time-division n~ultiplexing communication.
The f i r s t communication state control u n i t 112 manages a communication
state of the communication data 14, which has passed through the f i r s t
transmission path 131. The c o n ~ n ~ u n i c a t i osnta te is, for example, f a u l t
and maintenance information in Ehter OAM (Operation Administration
and Maintenance) in the all-packet network, a communication state,
information and t h e l i k e of a control frame in a protection function, such
as STP (Spanning Tree Protocol), ( t h e control frame referred t o a s a
5 BPDU frame in the case oE the STP). The f i r s t communication state
control unit 112 can be implemented by, for example, causing a CPU to
read and execute a FW (Firmware), which i s a computer program
implementing communication relay control processing.
[0020]
10 The second board 12 includes a second transmission control c i r c u i t
121 and a second communication state control unit 122. The second
transmission control c i r c u i t 121 controls usage of the second
transmission path 132 by the IF unit 10. The second coinmunication
state control unit 122 manages a communication state of the
15 communication data 14, which passes through the second transmission
path 132. Other configurations are similar to those of the f i r s t board 11
[0021]
As explained above, when the f i r s t board 11 is an active system,
the IF unit 10 transmits the communication data 14 to the f i r s t board 11
20 through t h e f i r s t transmission path 131, whereas when the second board
12 is t h e a c t i v e system, the IF unit 10 t r a n s m i t s t h e communication data
14 to the second board 12 through the second transmission path 132.
[0022]
Fig. 2 i s a.sequence diagram showing a flow of active system
25 switch processing upon detection of a f a u l t according to the f i r s t
exemplary embodiment of the present invention. Assume t h a t the
operation state of the first board 11 i s the active system, and the
operation state of the second board 12 is the standby system. However,
the operation will be sitnilar to the operation explained below even when
30 the operation states of t h e f i r s t board 11 and the second board 12 are
reversed.
100231
F i r s t , the f i r s t transmission control c i r c u i t 11 1 detects a f a u l t
inside the first board 11 (S11). Next, t h e f i r s t transmission control
circuit I l l gives an instruction to the 1F unit 10 as to whether or not
usage of the first transnlission path 131 is allowed (S12). Usually, since
the communication relay apparatus 1 is unable to continue a
comn~unicationr elay due to the fault inside the f i r s t board 11, the first
5 trans~nissionc ontrol c i r c u i t 111 gives an instruction to the IF unit 10 that
the usage of the f i r s t transmission path 131 is not allowed. In this
manner, the f i r s t transmission control c i r c u i t 111, which is a hardware
circuit, can stop the communication data 14 from being transmitted
through the f i r s t transmission path 131 to the f i r s t board 11, which is
10 likely to be incapable of performing normal processing, imnlediately after
detecting a fault.
[0024]
Moreover, together with Step S12, the first transmission control
circuit 11 1 n o t i f i e s the second transmission control c i r c u i t 121 and the
15 first communication state control unit 112 that the fault is detected (S13
and S14).
[0025]
Next, in response to the notification from the f i r s t transmission
control c i r c u i t 111, the second transmission control c i r c u i t 121 gives an
20 instruction to the IF unit 10 a s t o whether o r not the usage of the second
transmission path 132 i s allowed (S15). As mentioned above, since the
usage of the f i r s t transmission path 131 is not allowed in Step S12, under
normal circumstances, the second transmission control c i r c u i t 121 gives
, an instruction to the IF unit 10 that the usage of the second transnlission
25 path 132 i s allowed. After t h e f i r s t transmission control c i r c u i t 11 1
gives an instruction t h a t the usage of the f i r s t transmission path 131 is
not allowed, the second transmission control c i r c u i t 121, which is a
hardware c i r c u i t , promptly allows the usage of the second transnlission
path 132. Thus, the IF unit 10 can switch the transmission path from the
30 f i r s t transmission path 131 to the second transmission path 132. It is
therefore possible to continue to receive the communication data 14,
which has been received by the first board 11 before the f a u l t occurs,
using the second board 12 that is the standby system. Thus, for example,
whcn TDMSW is made redundant in the first board 11 and the second
board 12, the TDMSWs can be switched by the hardware circuits.
Accordingly, it is possible to realize switching in time-division
multiplexing communication within 50 ms.
[0026]
5 Moreover, the first commu~~icatiosnta te control unit 112 evaluates
a s t o whether o r not to switch the operation s t a t e of the f i r s t board 11 to
the standby system according to the notification from the first
transmission control c i r c u i t 11 1 (S 16). For example, the f i r s t
communication state control unit 112 evaluates as to whether o r not to
10 switch according to a s t a t e of communication that has been started before
the f a u l t i s detected, a content of a protocol or the like. Next, when the
f i r s t communication state control unit 121 makes an evaluation to switch
the operation s t a t e of the f i r s t board 11 to the standby system, the f i r s t
communication state control unit 112 starts to take over the
15 communication state of the communication data 14, which has passed
through the f i r s t transmission path 13 1, to the second communication
s t a t e c o n t r o l unit 122 (S17). After t h e takeover i s completed, the second
communication state control unit 122 changes the operation state of the
second board 12 to the active system. Further, the f i r s t communication
20 s t a t e c o n t r o l unit 112 changes the operation state of the first board 11 to
the standby system at least before the operation state of t h e second board
12 i s changed to the active system. In this manner, it i s possible to
realize accurate switching of the active system accompanying the
. takeover of the communication s t a t e a f t e r a f a u l t occurs in t h e f i r s t board
25 11. Therefore, when, for example, L2SW is made redundant i n t h e first
board 11 and the second board 12, the L2SWs can be switched by control
of the firmware. It is thus possible to accurately switch in the all-packet
network.
[0027]
3 0 Generally, as the takeover processing of the communication state is
executed by the firmware in thc control device, it takes more time for
processing than when i t i s executed by the hardware c i r c u i t . Therefore,
suppose t h a t whcn the transmission path i s switched a f t e r the takeover of
the conlmunication state is con~pleted,t he IF unit 10 continues to transmit
the comnlunication data 14 to the f i r s t board I I , which has a fault,
through the f i r s t transnlission path 13 1 after the f a u l t i s detected until the
handover i s completed. Thus, there may be a lack in the data transmitted
a f t e r the f a u l t i s detected until the takeover is completed o r the data may
5 not be correctly processed. As a result, a retransmission request and the
like is made by the IF unit 10 to outside, thereby possibly causing a delay
in a communication relay.
[0028]
Accordingly, i n t h e f i r s t exemplary embodiment of the present
10 invention, the t r a n s n ~ i s s i o np ath of the comnlunication data 14, which has
been continued before the f a u l t occurs, is quickly switched to the second
transmission path 132, so t h a t the communication data 14 is continuously
received by and can be at least held i n t h e second board 12, which i s the
standby system with no fault. After that, when the communication state
15 i s correctly taken over, processing of the communication data 14, which
has been held after the switching by the second communication state
control u n i t 122, i s collectively resumed, thereby minimizing a delay in
the communication relay.
[0029]
2 0 That is, in the first exemplary embodiment of the present invention,
since thc switching of the transmission path by the hardware c i r c u i t has
the highest priority, the t r a n s n ~ i s s i o no f the communication data 14,
which has been performed by the f i r s t board 11, is resumed early. By
.doing so, a minimum communication relay can be maintained. Further,
25 by performing t h e takeover of the communication state under control of
the firmware in the meantime, it i s possible to correctly continue the
communication relay after the active system i s switched.
[0030]
As explained above, according to the first exemplary embodiment
30 of the present invention, it i s possible to realize accurate takeover of the
communication state while maintaining the spced of switching in
switching control by the communication relay apparatus that performs a
communication relay in the time-division multiplexing and the all-packet
network
[003 11

Fig. 3 is a block diagram scl~ematically showing a communication
relay apparatus 2 according to a second exemplary embodiment of the
5 present invention. The communication relay apparatus 2 includes, for
example, a plurality of s l o t s disposed in a casing shown in Fig. 3 , and a
card, which is a board with a predetermined size and includes an
inputloutput i n t e r f a c e , i s removably mounted in each of the slots. Fig. 3
shows that a plurality of interface cards 20, device control cards 21 and
10 22, an auxiliary card 23 and the l i k e are mounted in the communication
relay apparatus 2. Note that the number of the dcvice control cards may
be three or more. Moreover, assume t h a t the device control card 21
includes, for example, a CPU 212, a TDM Switch 2101, a Packet Switch
2102 and the like.
15 [0032]
Fig. 4 is a block diagram showing main components of the
communication relay apparatus 2 according to the second exemplary
embodiment of the present invention. The communication relay
apparatus 2 is an apparatus that performs a communication relay of the
20 time-division multiplexing and the all-packet network. The
communication relay apparatus 2 includes the interface cards 20, the
device control cards 21 and 22, and the auxiliary card (TERMinal) 23.
Note t h a t an i l l u s t r a t i o n and explanation of other commonly-known
cnmponents that are necessary for the communication relay apparatus
25 shall be omitted.
[0033]
The auxiliary card 23 includes an NMS (Network Management
System) t h a t can be connected to the communication relay apparatus 1 and
an interface for communicating with other external devices as a DCN
30 (Data Communication Network). The auxiliary card 23 i s connected to
each of the device control cards 21 and 22.
[0034j
The interface card 20 and the device control card 21 are connectcd
by a main signal bus 231 and a control bus 232. Moreover, the interface
card 20 and the device control card 22 are connected by a control bus 233
and a main signal bus 234. The main signal buses 231 and 234 are
examples of the f i r s t transmission path 13 1 and the second transmission
path 132 in Fig. 1 and are transn~issionp aths for transmitting
5 con~municationd ata to be relayed by the communication relay apparatus 2
as a main signal. Further, when the main signal has data of the
time-division multiplexing and all-packet network, each of the main
signal buses 231 and 234 may include two transmission paths for the
time-division multiplexing and all-packet network. The control buses
10 232 and 233 are transmission paths for transmitting various control
signals from the device control cards 21 and 22.
[0035]
The interface card 20 i s one example of the IF unit 10 in Fig. 1 and
includes a selector 201 and an ACT signal detection unit 202. The
15 selector 201 i s connected to a main signal transmission unit 211 of the
device control card 21 by the main signal bus 231. Moreover, the
selector 201 i s connected to the main signal transmission u n i t 221 of the
device control card 22 by the main signal bus 234. The ACT signal
d e t e c t i o n u n i t 202 i s connected to an FPGA 212 of the device control card
20 21 by the control bus 232. Moreover, the ACT signal detection u n i t 202
i s connected to an FPGA 222 of the device control card 22 by the control
bus 233.
[0036]
The ACT signal detection u n i t 202 receives a control signal (an
25 ACT signal) indicating as to whether usage of the main signal bus 231 is
allowed through t h e control bus 232 and receives a control signal (an ACT
signal) indicating a s t o whether usage of the main signal bus 234 is
allowed through the control bus 233. The selector 201 selects o n e o f the
main signal buses 231 and 234 based on the control signals received by
30 the ACT s i g n a l d e t e c t i o n unit 202 and transmits the communication d a t a .
[0037]
The device control card 21 is one example of the first board 11 in
Fig. 1. The device control card 21 includes the main signal t r a n s n ~ i s s i o n
unit 211, the FPGA 212 and a CPU 213. The main signal transmission
unit 211 i s a t r a n s n ~ i s s i o nc i r c u i t t h a t transmits a main signal to the
interface card 20 through the main signal bus 23 1. The main signal
transmission unit 21 1 may include, f o r example, a TDMSW for
transmitting communication data o f the timc division multiplexing and an
5 L2SW f o r transmitting communication data o f the all-packet network.
[0038]
The FPGA 212 i s one example of the f i r s t transmission control
circuit 111 in Fig. 1 . The FPGA 212 i s a circuit t h a t t r a n s m i t s a c o n t r o l
signal to the interface card 20 through the control bus 232. The CPU
10 213 is one examplc of the first communication s t a t e c o n t r o l unit 112 in
Fig. 1. The CPU 213 performs communication relay control processing
by reading and executing the above-mentioned FW.
[0039]
The device c o n t r o l card 22 i s one example of the second board 12
15 in Fig. 1. The device c o n t r o l card 22 includes the main signal
transmission unit 221, the FPGA 222 and the CPU 223. The FPGA 222 is
one example o f the second transmission control circuit 121 in Fig. 1.
The CPU 223 i s one example'of the second communication s t a t e c o n t r o l
unit 122 in Fig. 1. The main signal transmission u n i t 221, the FPGA 222,
20 and the CPU 223 have a f u n c t i o n equivalent t o those of the main signal
transmission unit 211, the FPGA 212, and the CPU 213, respectively.
[0040]
Moreover, the device c o n t r o l c a r d s 21 and 2 2 a r e connected by a
. DC line 24 and Ethernet (registered trademark) 25. Thus, the FPGAs
25 212 and 222 transmit and receive various c o n t r o l s i g n a l s through the DC
line 24. Further, the CPUs 213 and 223 transmit and receive a
comnlunication state and the like via the Ethernet 25.
[0041]
Now the features and advantageous e f f e c t s of the second exemplary
30 embodiment according to the present invention shall be explained. First,
when the FPGA 212 d e t e c t s a fault in the device c o n t r o l card 21 while the
operation s t a t e o f the device c o n t r o l card 21 is the activc system, the
FPGA 212 gives an instruction t o the interface card 20 as t o whether or
not the usage o f the main s i g n a l bus 231 is allowed and also n o t i f i e s the
FPGA 222 and the CPU 213 t h a t t h e f a u l t i s detected. Then, in response
to the notification from the FPGA 212, the FPGA 222 gives an instruction
to the interface card 20 as to whether o r not the usage of the main signal
bus 234 is allowed. Moreover, in response to the notification from the
5 FPGA 212, the CPU 213 evaluates a s t o whether o r not to switch t h e
operation s t a t e of the device control card 21 to the standby system.
When an evaluation i s made to switch to the standby system, the CPU 213
starts to take over the communication state of the communication data,
which has passed through the main signal bus 231, to the CPU 223. It is
10 thus possible to achieve an advantageous effect similar to that of the first
exemplary embodiment.
[0042]
Furthermore, the FPGA 222 n o t i f i e s the FPGA 212 of existence or
absence of a fault in the device control card 22. When the FPGA 212
15 detects a fault in the device control card 21 while the operation state of
t h e device control card 21 is t h e a c t i v e system, the FPGA 212 evaluates as
to whether or not the usage of the main signal bus 231 i s allowed
according to existence o r absence of a fault in the device control card 22
and gives an instruction to the interface card 20 based on the evaluation
20 result. As described so far, by performing a switching evaluation using
the hardware c i r c u i t taking into account a fault in t h e a c t i v e system and
the standby system, it i s possible to handle the case in which a f a u l t
exists in both systems. For example, when there i s a fault in both
. systems, even when.switching is performed immediately, i t might not be
25 possible to continue the communication relay i n t h e switched board.
Therefore, in such a case, a switching evaluation i s performed t h r o u g h a
detailed analysis using a CPU on a subsequent c i r c u i t side without
forcefully switching the board by the hardware c i r c u i t , thereby making it
possible to avoid unnecessary switching.
30 [0043]
Furthermore, when the operation state of the device control card 21
i s switched, the CPU 213 determines a switch pattern for the FPGA 212 to
switch between whether or not the usage of the main signal bus 231 is
allowed according to the switched operation state and sets the determined
switch pattern in the FPGA 212. When the FPGA 212 detects a f a u l t in
the device control card 21 or receives the notification from the FPGA 222
t h a t a fault is detected, the FPGA 212 i d e n t i f i e s whether or not the usage
of the main signal bus 231 is allowed according t o t h e switch pattern that
5 has been set by the CPU 213 and a combination o f existence or absence of
a fault in the device control card 21 and existence or absence of a f a u l t in
the device control card 22, and gives an instruction of a r e s u l t o f the
identification t o the interface card 20. Thus, as the FPGA 212
autonomously performs an evaluation using only two pieces of fault
10 information and switches the main s i g n a l bus 231, high speed processing
is possible.
[0044]
Moreover, when a f a u l t i s detected in the device control card 21
that cannot be detected by the FPGA 212, the CPU 213 n o t i f i e s the FPGA
15 212 t h a t the f a u l t i n the device control card 21 is detected. When the
FPGA 212 receives the notification from the CPU 213, the FPGA 212
detects the fault as a fault in the device c o n t r o l card 21. In this manner,
a f a u l t t h a t cannot be detected by the hardware c i r c u i t alone is detected
by the FW, thereby making it possible t o switch the operation s t a t e i n a
20 s i m i l a r manner t o when a f a u l t i s detected by the hardware c i r c u i t alone.
That i s , the FW can make a comprehensive e v a l u a t i o n .
[0045]
Further, in response t o the notification from the FPGA 212, the
.FPGA 222 f u r t h e r n o t i f i e s the CPU 223 that. the device control card 21 is
25 faulty. At t h i s t i m e , in response to the notification from the FPGA 222,
the CPU 223 changes the operation s t a t e o f the device control card 22 t o a
state not allowed to be switched ( t h e operation s t a t e i s forcefully fixed)
and notifies the CPU 213 t o t h a t e f f e c t . Then, i n response t o the
notification from the CPU 223, the CPU 213 transfers the communication
30 state of the communication data, which has passed through the main
signal bus 231, to the CPU 223. Next, after the CPU 223 c o n ~ p l e t e s
s e t t i n g o f the communication s t a t e t h a t has been transferred from the CPU
213, the CPU 223 switches the operation state of the device control card
22 to the active system. In this manner, it i s p o s s i b l e to prevent failback
due to double f a u l t , such that after a f a u l t occurs in an operation system,
a f a u l t is incorrectly recognized in a standby system, thereby enabling a
stable switching of thc operation s t a t e .
[0046]
5 Fig. 5 is a diagram showing an example of operation s t a t e s of the
device control card according to the second exemplary embodiment of the
present invention. Fig. 5 shows, for example, seven operation s t a t e s ,
which are "UNMOUNT", " I N I T " , "ACT", "SBY (StandBY)", "ACT-FLT
(FauLT)", "SBY-FLT", and " 0 0 s (Out Of Service)". Moreover, the
10 operation s t a t e s of "FORCED ACT" and "FORCED SBY" may also be
internally used as states to temporarily change during the switching.
Note t h a t the operation state is not limited to t h o s e examples of the
operation s t a t e s .
[0047]
15 Fig; 6 i s a block diagram showing main components of the device
control card according to the second exemplary embodiment of the
present invention. In Fig. 6 , an internal configuration of the device
control card 21 i s focused on, and as for other configuration, only the
related parts are i l l u s t r a t e d .
20 [0048]
The device control card 21 includes the CPU 213, an FW
(Firmware) detecting own-system Fail 214, an HW (Hardware) detecting
own-system Fail signal 215, an OR c i r c u i t 216, a Pattern 217, a State
Machine 218, an OR circuit 219 and the like.
25 100491
The FW detecting own-system Fail 214 is a r e g i s t e r that records
existence o r absence of a f a u l t t h a t cannot be detected by the hardware
circuit and detected by the FW. Specifically, the CPU 213 updates a f l a g
of this register. The HW detecting own-system Fail signal 215 is a
30 signal indicating existence o r absence of a f a u l t that is detected by the
hardware c i r c u i t . Note that the hardware c i r c u i t t h a t detects a f a u l t
inside the device control card 21 shall be included in the FPGA 212. The
OR c i r c u i t 216 is a c i r c u i t for obtaining an OR between the flag of the FW
detecting own-system Fail 214 and the Fail signal 215. Hereinafter, an
output signal of the OR circuit 216 is referred to as an own-system FLT
(FauLT) signal S I G l l . Thc own-system FLT signal S I G l l indicates
existence o r absence of a fault in the device control card 21. The
own-system FLT signal SIGI I i s input to the CPU 213, the State Machine
5 218, and the device control card 22. Note that the device control card 22
receives the own-systen~ FLT signal S I G l l from the device control card
21 as a Fail signal SIG28 of the other system.
[0050]
The Pattern 217 is a register that records a switch pattern t h a t i s
10 determined according to the operation state of the device control card 21.
[005 11
The OR circuit 219 is a c i r c u i t t h a t inputs a plurality of signals
regarding a fault in the device control card 22, which i s the other system,
and outputs an OR of those signals as an other-system FLT signal SIG12.
15 As the plurality of signals regarding a fault i n t h e other system here, a
power OFF signal SIG24 indicating power-down of the device control
card 22, an unmount signal SIG25 indicating t h a t the device control card
22 is unmounted from the communication relay apparatus 2, and a Fail
signal SIG21 indicating an own-system FLT of the device control card 22
20 are illustrated. Note that the signals regarding a fault in the other
system are not limited to these.
[0052]
The State Machine 218 evaluates as to whether o r not the usage of
the main signal bus 231 is allowed according to the own-system FLT
25 signal S I G l l , the other-system FLT signal SIG12, and t h e switch pattern
recorded in the Pattern 217, and outputs the evaluation as an ACT signal
SIG13. The ACT signal SIG13 i s input to the CPU 213, the device
control card 22, the interface card 20, and the auxiliary card 23. Note
that t h e device control card 22 receives the ACT signal SIG13 from the
30 device control card 21 as an ACT signal SIG29 of the other system. The .
State Machine 218 evaluates as to whether o r not the usage of the main
signal 213 i s allowed according t o , for example, an evaluation rule of the
ACT signal show11 in Fig. 7.
I00531
F i g . 7 is a diagram showing an example o f the evaluation rule o f
thc ACT signal according to the second exemplary embodiment o f the
present invention. In F i g . 7, whether the ACT signal is turned ONIOFF
is shown in association with combinations o f ONIOFF o f the own-system
5 FLT signal and the other-system FLT signal and ACT operation patterns 0
to 15.
lo0541
Fig. 8 is a diagram showing an example o f a correspondence
relation between the operation states and t h e ACT operation patterns
10 according to the second exemplary embodiment o f the present invention.
The CPU 213 can record one o f the seven patterns, which are from "INIT"
to "FORCED SBY" from among the above-mentioned operation states
shown in F i g . 5, in the Pattern 217. However, when all o f the operation
states are recorded to create the ACT operation patterns, the number o f
15 conlbinations shown in Fig. 7 w i l l b e enormous, t h e r e b y increasing the
size o f the circuit o f the State Machine 218. Moreover, some o f the
seven operation states can have the same pattern o f the ACT signal
operation as a r e s u l t o f an evaluation according to the fault information
o f the own system and the other system. T h u s , the associations between
20 t h e s e v e n operation states and the four ACT operation patterns are
defined as shown in Fig. 8, and Fig. 7 is defined based on Fig. 8. A f t e r
t h e operation state o f t h e d e v i c e control card 21 is switched, the CPU 213
determines the ACT operation pattern using the switched operation state
based on the associations o f Fig. 8. Then, the CPU 213 records the
25 determined ACT operation pattern in the Pattern 217. In this manner,
the size o f the circuit o f the State Machine 218 can be controlled. In
addition, since an output o f an ACT line can bc evaluated by only the
fault information o f the own system and other system in processing b y t h e
FPGA, the speed o f the processing can be increased. Note that the
30 associations o f Fig. 8 are not limited to those explained above. Those
associations can be updated by, for example, changing the setting o f the
FPGAs 212 and 222.
[0055]
An example shall be explained below. When the opcration state o f
the device control card 21 is "ACT", the operation s t a t e o f the device
control card 22 is "SBY", the device control card 21 is faulty, and the
device control card 22 is not faulty, in the FPGA 212, if the ACT
operation pattern is "Il(OxB)", the own-system FLT signal SIGlI=ON and
5 the other-system FLT signal SIG12=OFF. Thus thc ACT signal
SIG13=OFF. Meanwhile, in the FPGA 222, when the ACT operation
pattern is "2(0x2)", thc own-system FLT signal ( F a i l signal SIG21)=OFF
and the other-system FLT signal (OR o f the power OFF s i g n a l SIG26, the
unmount signal SIG27, and the F a i l signal SIG 28)=ON. Thus the ACT
10 signal SIG 23=ON.
[0056]
Referring back t o F i g . 6, the explanation shall be continued. The
CPU 213 inputs the ACT s i g n a l SIG13 from the State Machine 218, the
ACT signal SIG23, the own-system FLT signal S I G l l , and the
15 other-system FLT signal SIG12 from the device control card 22. In
particular, when the CPU 213 receives the own-system FLT signal S I G I l
or the other-system FLT signal SIG12, the CPU 213 analyzes a content o f
the fault in the own system and the other system and comprehensively
evaluates as t o whether it is necessary to switch the operation state.
20 [0057]
Moreover, the device c o n t r o l card 22 inputs the power OFF signal
SIG14, the unmount signal SIG15, the own-system FI,T signal S I G l l , and
the ACT signal SIG13 from the device control card 21 a s the other-system
signals, and outputs the power OFF signal SlG24, the unmount signal
25 SIG25, the Fail signal SIG21, and the ACT signal SIC23 to the device
control card 21. Note t h a t the device c o n t r o l card 22 receives the power
OFF signal SIG14 and the unmount signal SIG15 from the device c o n t r o l
card 21 a s the power OFF signal SIG26 and the unmount s i g n a l SIG 27 o f
the other system.
30 [0058]
Fig. 9 i s a sequence diagram showing a flow of operation system
switch processing upon detection of a f a u l t according t o the second
exemplary embodiment of the present i i ~ v e n t i o n . In the following
explanation, r e f e r t o Figs. 11 to 16 as appropriate. Figs. 11 to 16 are
diagrams showing an example o f an active system switch operation upon
detection o f a f a u l t according t o the second exemplary embodinlent o f the
present invention. Assume t h a t the operation statc of the device control
card 21 is "ACT", while the operation state o f the device s t a t e card 22 is
5 "SBY". Therefore, in Fig. 11, the CPU 213 recognizes t h a t the operation
s t a t e ( h e r e i n a f t e r referred t o a s a "mode") ml is "ACT", and the FPGA
212 recognizes that the ACT operation pattern (hereinafter referred t o as
a " p a t t e r n " ) p l is "OxB." Moreover, the CPU 223 recognizes t h a t a mode
m2 is "SBY", and the FPGA 222 recognizes a pattern p2 is "0x2."
10 Further, since the ACT signal from the device control card 21 is "ON", the
selector 201 inside the interface card 20 selects the main s i g n a l bus 231.
Furthermore, the device control card 21 performs communication relay
processing, and the CPU 213 holds a communication state CS. Assume
t h a t a p a r t o f the device c o n t r o l card 21 becomes faulty at t h i s t i m e .
15 Firstly, the FPGA 212 d e t e c t s the f a u l t inside the device c o n t r o l c a r d 21
(S201, F i g . 1 1 ) .
[0059]
Next, the FPGA 212 outputs the ACT s i g n a l SIG13=OFF t o the
interface card 20 (S202, Fig. 12). Specifically, a s the own-system FLT
20 SIGll=ON, and the other-system FLT SIG12=OFF, and the ACT operation
p a t t e r n i s "ll(OxB)", the FPGA 212 e v a l u a t e s the ACT signal SIG13 t o he
"OFF" according to Fig. 7. Next, the FPGA 212 outputs the ACT signal
SIG13=OFF t o the interface card 20 through the control bus 232. Then,
the s e l e c t o r 201 immediately stops using the main signal bus 231.
25 [0060]
At the same t i m e , the FPGA 212 n o t i f i e s the FPGA 222, which is
t h e o t h e r system, of the f a u l t (S203, Fig. 12). Specifically, the FPGA
212 outputs the own-system FLT signal S I G l l ( F a i 1 signal)=ON through
the DC l i n e 24. Then, the device c o n t r o l card 22 can recognize that the
30 f a u l t h a s occurred in the device control card 21. Furthermore, the FPGA
212 notifies the CPU 213 o f the f a u l t i n the own system (S204, Fig. 12).
Specifically, the FPGA 212 outputs the own-system FLT signal SIGll=ON
to the CPU 213.
[006 11
Next, the FPGA 222 outputs the ACT signal SIG23=ON to the
interface card 20 ( S 2 0 5 , Fig. 13). S p e c i f i c a l l y , in the FPGA 222, since
the ACT operation pattern is "2(0 x 2 ) " , the usage o f t h e main signal bus
234 i s not allowed at t h i s point, and the ACT signal SIG23 is in the state
5 o f "OFF." Further, since t h e own-system FLT signal (Fail signal
SIG21)=OFF, and the other-system FLT (Fail signal SIG28)=ON by the
fault n o t i f i c a t i o n from t h e d e v i c e control card 2 1 , w h i c h is the other
system for the device control card 22, t h e ACT signal SIG23 is evaluated
to be "ON". N e x t , the FPGA 212 outputs t h e ACT signal SIG23=ON to
10 the interface card 20 through the control bus 233. Then, the selector 201
immediately starts using the main signal b u s 2 3 4 . That i s , t h e i n t e r f a c e
card 20 switches a s e l e c t i o n o f the transmission path f r o m t h e main signal
bus 231 to the main signal bus 234 ( S 2 0 7 , Fig. 13).
[0062]
15 At the same t i m e , the FPGA 222 n o t i f i e s t h e CPU 223 o f the fault
in the other system ( S 2 0 6 , Fig. 13). S p e c i f i c a l l y , t h e FPGA 222 outputs
t h e o t h e r - s y s t e m FLT signal=ON to the CPU 223.
[0063]
A f t e r t h a t , each o f the CPUs 213 and 223 performs fault analysis
20 processing (S208 and S209). Fig. 10 is a flowchart showing a flow o f
the fault analysis processing according to the second exemplary
embodiment o f the present invention. An explanation o f the CPU 213
shall be g i v e n now.
[0064] ,
2 5 Firstly, the CPU 213 checks detailed information o f an own-system
fault ( S 3 0 1 ) . Moreover, the CPU 213 checks detailed information o f an
other-system fault ( S 3 0 2 ) . The CPU 213 reads the detailed information
o f t h e o w n - s y s t e m fault and t h e o t h e r - s y s t e m fault that is written in, for
example, a register inside the device control card 21, and evaluates a
30 l o c a t i o n , a content, a degree and the l i k e o f the fault. Note that the CPU
213 i s n o t i f i e d o f the content o f the fault as appropriate by t h e d e v i c e
control card 22 via the Ethernet 25 or the l i k e , and the content or the like
is recorded.
[0065]
Next, the CPU 213 evaluates as to whether o r not to switch the
operation s t a t e (S303). As the operation s t a t e of the device control card
21 is "ACT", which indicates the active system, the CPU 213 evaluates as
to whether or not to switch to the standby system. When the device
5 control card 21 is no longer able to continue the communication service
according to the content of the f a u l t in the own system and no f a u l t i s
occurring in the other system based on Steps S301 and S302, the CPU 213
evaluates that the operation state of the device control card 21 is
switched to the standby system.
10 [0066]
When an evaluation i s made to switch, the CPU 213 evaluates as to
whether o r not the device control card 21 i s subject to take over the
communication state (S304). Since the device control card 21 i s the
active system, the CPU 213 evaluates t h a t the device control card 21 is
15 subject to take over the communication state and determines the operation
state of the device control card 21 to be "SBY-FLT" (S305).
[0067]
Moreover, in the case of the CPU 223 of the device control card 22,
an evaluation i s made t h a t the device control card 22 i s not subject to take
20 over the communication state in Step S304 and determines the operation
state of t h e device control card 22 to be "FORCED ACT" (S306).
[0068]
Note that when an evaluation i s made not to switch in Step S303,
the CPU 2.13 ends the processing. While the device control card 22,
25 which has originally been SBY, enters a faulty s t a t e ( i s changed to
SBY-FLT), when a f a u l t occurs in the device control card 21, which i s in
the state of ACT, both systems will become faulty. However in this case,
as f o r t h e operation of the FPGA 212, since the own-system FLT signal
SIGl ]=ON and the other-system FLT signal SIG12=ON when the ACT
30 operation pattern i s "ll(OxB)", the ACT signal SIG13 remains ON, and
the CPU 213 evaluates t h a t it is not necessary to switch and the operation
state of the device control card 21 is "ACT-FLT" and may change
[0069]
Referring back to Fig. 9 , the explanation s h a l l be continued. The
CPU 223 is changed to the operation s t a t e "FORCED ACT" t h a t i s
determined in Step S209 (S210, Fig. 14). Specifically, the CPU 223
records "FORCED ACT" in the register inside the Fl'GA 222, and the
FI'GA 222 recognizes t h a t the pattern p2 is "OxF." After t h a t , the CPU
5 223 n o t i f i e s the CPU 213 t h a t the s t a t e change has been completed (S211,
Fig. 14). Then, the CPU 213 is changed t o the operation state
"SBY-FLT" that is determined in Step S208 (S212, Fig. 14). Specifically,
the CPIJ 213 records "SBY-FLT" in the r e g i s t e r inside the FPGA 212, and
the FPGA 212 recognizes that the pattern pl is "0x0."
10 [0070]
After t h a t , the CPU 213 transmits the communication s t a t e CS to
the CPU 223 (S213, Fig. 15). Then, the CPU 223 sets the transferred
communication state CS i n the device control card 22 (S214). After t h a t ,
the CPU 223 changes the operation state of the device control card 22 t o
15 "ACT" (S215, Fig. 16). Specifically, the CPU 223 records "ACT" in the
r e g i s t e r inside the FPGA 222, and the FPGA 222 recognizes that the
pattern p2 is "OxB."
[0071]
As explained so far, even when a f a u l t occurs in the device c o n t r o l
20 card 21, the FPGAs 212 and 222, which a r e t h e hardware c i r c u i t s ,
immediately switch OFFION of the ACT s i g n a l , and the selector 201 can
continue t o transmit the communication data through the switched main
signal bus 234. Since the switching by the FPGA 212 and 222 can be
realized within 50 ms, a delay i n the communication can be minimized.
25 Moreover, as it is not r e a l i s t i c to take over the communication s t a t e CS by
the hardware c i r c u i t s , the takeover c a n b e accurately performed between
the CPUs 213 and 223 via the Ethernet 25. Therefore, as soon as the
communication s t a t e CS i s taken over to the device control card 22,
comn~unicationr elay can be resumed correctly.
30 [0072]
Note that the present invention is not linlited by the above
exenlplary enlbodinlents and appropriate modifications can be made
without departing fro111 t h e s c o p e thereof.
[0073]
The p r e s e n t a p p l i c a t i o n c l a i m s priority rights of and is based on
J a p a n e s e P a t e n t A p p l i c a t i o n N o . 2011-237985 filed on Oct 2 8 , 2011 in the
J a p a n e s e P a t e n t Office, the entire contcnts of which are hereby
incorporated by r e f c r e n c e .
5
I n d u s t r i a l A p p l i c a b i l i t y
[0074]
The p r e s e n t invention is useful as a r a d i o communication a p p a r a t u s
i n which when a communication a p p a r a t u s 011 a t r a n s m i s s i o n s i d e c a n n o t
10 d i r e c t l y comlnunicate w i t h a communication a p p a r a t u s 011 a r e c e p t i o n s i d e ,
a relay apparatus r e l a y s and transmits a s i g n a l between these
commttnication apparatuses.
R e f e r e n c e S i g n s List
15 [0075]
1 COMMUNICATION RELAY APPARATUS
10 IF UNIT
11 FIRST BOARD
11 1 FIRST TRANSMISSION CONTROL CIRCUIT
2 0 1 1 2 FIRST COMMUNICATION STATE CONTROL UNIT
1 2 SECOND BOARD
121 SECOND TRANSMISSION CONTROL CIRCUIT
1 2 2 SECOND COMMUNICATION STATE CONTROL UNIT
13 1 FIRST.TRANSMISSION PATH
25 132 SECOND TRANSMISSION PATH
14 COMMUNICATION DATA
2 COMMUNICATION RELAY APPARATUS
2 0 INTERFACE CARD
201 SELECTOR
30 202 ACT SIGNAL DETECTION UNIT
2 1 DEVICE CONTROL CARD
2101 TDM SWITCH
2102 PACKET SWITCI-I
21 1 MAIN SIGNAL TRANSMISSION UNIT
212 FPGA
213 CPU
214 FW DETECTING OWN-SYSTEM F a i l
215 NW DETECTING OWN-SYSTEM F a i l SIGNAL
5 216 OR CIRCUIT
217 PATTERN
218 STATE MACHINE
219 OR CIRCUIT
22 DEVICE CONTROL CARD
10 221 MAIN SIGNAL TRANSMISSION UNIT
222 FPGA
223 CPU
2 3 AUXILIARY CARD
231 MAIN SIGNAL BUS
15 232 CONTROL BUS
233 CONTROL BUS
234 MAIN SIGNAL BUS
24 DC LINE
2 5 Ethernet
20 ml MODE
P 1 PATTERN
m2 MODE
~2 PATTERN
CS COMMUNICATION STATE
25 ST000, ST004, ST005, ST010, ST012, ST014, ST015, ST030, ST034,
ST035, ST140, ST150, S T l O l , ST121, ST141, ST151, ST103, ST143, and
ST153 STATE
S I G l l OWN-SYSTEM FLT SIGNAL
SIG12 OTHER-SYSTEM FLT SIGNAL
30 SIG13 ACT SIGNAL
SIG14 POWER OFF SIGNAL
SIGl5 UNMOUNT SIGNAI,
SIG21 FAIL SIGNAL
SIG23 ACT SIGNAL
SIG24 I'OWER OFF SIGNAL
SIG25 UNMOUNT SIGNAL
SIG26 POWEIi OFF SIGNAL
SIG27 UNMOUNT SIGNAL
5 SIG28 FAIL SIGNAL
SIG29 ACT SIGNAL
WE CLAIM:
1 . A communication relay apparatus comprising:
an IF unit that externally transmits and receives c o n ~ n ~ u n i c a t i o n
5 data;
a first board that comprises:
a f i r s t transmission control circuit that is connected to the
IF unit by a first transmission path and controls usage o f the first
transmission path by the IF u n i t ; and
10 a first communication state control unit t h a t manages a
communication state o f the communication data that has passed through
the first transmission path; and
a second board that is mounted as a redundant board o f the first
board and comprises:
15 a second transmission control c i r c u i t t h a t is connected to the
IF unit by a second transmission path and controls usage o f the second
transmission path by the IF unit; and
a second communication state control unit t h a t manages a
communication state o f the communication data that has passed through
20 the second transmission path, wherein
when an operation state o f the first board is an active system and
the first transmission control c i r c u i t detects a fault in the f i r s t board, the
first transmission control circuit gives an instruction to the IF unit as to
. whether or not the usage o f the first transmission path is allowed and
25 n o t i f i e s t h e second transmission control circuit and the first
con~nlunications tate control u n i t t h a t the fault i s d e t e c t e d ,
in response to a n o t i f i c a t i o n from the first transmission control
circuit, the second transmission control circuit gives an instruction to the
IF unit as to whether or not the usage o f the second transmission path is
30 allowed,
the first communication state control unit evaluates as to whether
or not to switch the operation state o f the first board to a standby system,
and
when an evaluation is made to s w i t c h t h e operation state o f the
first board to the standby system, the f i r s t communication state control
unit starts to take over the communication state of the conln~unication
data, which has passed through the f i r s t transmission path, to the second
coinn~unication state control unit.
5
2. The conlmunication relay apparatus according to Claim 1;
wherein
the second transmission control c i r c u i t n o t i f i e s the first
transmission control c i r c u i t of existence or absence of a f a u l t in the
10 second board,
when the operation state of the f i r s t board is t h e a c t i v e system and
the first transmission control c i r c u i t detects a f a u l t in the first board, the
f i r s t transmission control c i r c u i t evaluates a s t o whether or not the usage
of the f i r s t transmission path i s allowed according to existence or absence
15 of a f a u l t in the second board, and
the first transmission control c i r c u i t gives an instruction to the IF
unit based on an evaluation r e s u l t .
3. The communication relay apparatus according to Claim 2,
20 wherein
when t h e operation s t a t e of the f i r s t board is switched, the first
communication state control unit determines a switch pattern f o r t h e first
transmission c i r c u i t to switch between whether o r not the usage of the
, first transmission p,ath i s allowed based on the switched operation state
25 and sets the determined switch pattern in the f i r s t transmission control
circuit,
when the f i r s t transmission control c i r c u i t detects a f a u l t in the
first board o r receives, from the second transmission control c i r c u i t , a
notification t h a t a f a u l t i s detected, the first transmission control c i r c u i t
30 i d e n t i f i e s whether o r not the usage of the f i r s t transmission path i s
allowed according to the switch pattern t h a t has been set by the first
col~tmunications tate control u n i t and a combination of existence o r
absence of a fault i n t h e first board and existence or absence of a f a u l t in
the second board, which i s notified by t h e second transmission control
circuit, and
the first transmission control c i r c u i t givcs an instruction of a
rcsult of the identification to the IF unit.
4. The communication relay apparatus according to any one of
Claims 1 to 3, wherein
when the f i r s t con~munication state control u n i t detects a fault,
which cannot be detected by the first transnlission control c i r c u i t , in the
first board, the first c o n ~ n ~ u n i c a t i osnta te control unit n o t i f i e s the first
10 translnission control c i r c u i t that the f a u l t i s detected in the f i r s t board,
and
when the f i r s t transmission control c i r c u i t receives a notification
from the f i r s t communication state control u n i t , the first transmission
control c i r c u i t detects the f a u l t as a fault in the first board.
15
5. The communication relay apparatus according to any one of
Claims 1 to 4, wherein
in response to the notification from the first transmission control
c i r c u i t , the second transmission control c i r c u i t further n o t i f i e s the second
20 communication state control unit that the first board is faulty,
in response to a notification from the second transmission control
c i r c u i t , the second communication s t a t e control unit changes an operation
state of the second board to a s t a t e not allowed to be switched and
. notifies the f i r s t communication state control u n i t to t h a t e f f e c t ,
2 5 in response to a notification from the second comn~unication state
control u n i t , the first conln~unication state control unit transfers the
communication state of the communication d a t a , which has passed
through the f i r s t transmission path, to the second communication s t a t e
control unit, and
3 0 a f t e r the second co~nmunication state control unit c o n ~ p l e t e s
setting of the communication s t a t e , which has been transferred from the
first comnlunication state control u n i t , the second communication s t a t e
control unit switches the operation state of the second board to the active
system.
6 . A nletltod of switching an active system using a con~munication
relay apparatus that comprises:
an IF unit that externally transmits and receives communication
5 data;
a first board that comprises:
a first transmission control circuit that i s connected to the
IF unit by a first transmission path and controls usage of the f i r s t
transmission path by the IF unit; and
10 a first communication state control unit t h a t manages a
con~munication state of the communication data t h a t has passed through
the f i r s t transmission path; and
a second board t h a t i s mounted as a redundant f i r s t board and
comprises:
15 a second transmission control c i r c u i t that is connected to the
IF unit by a second transmission path and controls usage of the second
transmission path by the IF unit; and
a second communication state control unit t h a t manages a
communication s t a t e of the communication data t h a t has passed through
20 the second transmission path, the method comprising:
when an operation state of the first board is an active system and
the first transmission control c i r c u i t detects a f a u l t in t h e f i r s t board, by
the f i r s t transmission control c i r c u i t , giving an instruction to the IF unit
a s t o whether o r not t h e usage of t h e f i r s t transmission path is allowed
25 and notifying the second transmission control c i r c u i t and the f i r s t
communication state control u n i t t h a t the f a u l t i s detected,
in response to a notification from the first translnission control
circuit, by the second transmission control c i r c u i t , giving an instruction
to the IF unit a s t o whether o r not the usage of the second transmission
30 path i s allowed,
by the f i r s t communication slate control unit, evaluating as to
whether o r not to switch the operation state of the first board to a standby
system, and
when an evaluation i s made to switch the operation state of the
first board to the standby system, by the f i r s t communication s t a t e c o n t r o l
unit, starting to takc over the communication state of the communication
data that has passed through the f i r s t transmission path.
7. The method according to Claim 6 , wherein
the second transmission control c i r c u i t n o t i f i e s the f i r s t
transmission control c i r c u i t of existence o r absence of a f a u l t in the
second board,
when the operation state of the f i r s t board i s the active system and
10 the first transmission control c i r c u i t detects a f a u l t in the f i r s t board, the
f i r s t transmission control c i r c u i t evaluates a s t o whether or not the usage
of the first transmission path i s allowed according to existence or absence
of a f a u l t in the second board, and
the first transmission control c i r c u i t gives an instruction to the IF
15 unit based on an evaluation r e s u l t .
8. The method according to Claim 7, wherein:
when the operation state of the first board i s switched, t h e f i r s t
communication state control u n i t determines a switch pattern for the first
20 transmission c i r c u i t to switch between whether o r not the usage of the
f i r s t transmission path i s allowed based on the switched operation state
and sets the determined switch pattern in the f i r s t transmission control
circuit,
when the f i r s t transmission c o ~ l t r o l circuit detects a f a u l t in the
25 first board o r receives, from the second transmission control c i r c u i t , a
notification t h a t a f a u l t is detected, the f i r s t transmission control c i r c u i t
i d e n t i f i e s whether o r not the usage of the f i r s t transmission path i s
allowed according to the switch pattern that has been set by the f i r s t
communication state control unit and a combination of existence o r
30 absence of a f a u l t in the first board and existence o r absence of a f a u l t in
the second board, and
the first transmission control c i r c u i t gives an instruction of a
result of the identification to the IF unit.
9. The method according to any one of Claims 6 to 8, wherein
when the first communication state control tinit detects a f a u l t ,
which cannot be detected by the f i r s t transmission control c i r c u i t , in the
first board, the first communication state control unit n o t i f i e s the f i r s t
5 transmission control c i r c u i t that the fault is detected in the f i r s t board,
and
when the first transmission control c i r c u i t receives a notification
from the first communication s t a t e control unit, the first transmission
control circuit detects ihe fault as a f a u l t in the f i r s t board.
10
10. The method according to any one of Claims 6 to 9, wherein
in response to the notification from the first transmission control
c i r c u i t , the second transmission control c i r c u i t further n o t i f i e s the second
communication state control unit t h a t t h e f i r s t board is faulty,
15 in response to a notification from the second transmission control
c i r c u i t , the second communication state control unit changes an operation
state of the second board to a state not allowed to be switched and
n o t i f i e s the f i r s t communication state control u n i t to t h a t e f f e c t ,
in response to a notification from the second communication state
20 control unit, the first communication state control unit t r a n s f e r s t h e
communication state of the communication d a t a , which has passed
through the f i r s t transmission path, to the second communication state
control unit, and
. a f t e r the second co,mmunication state control u n i t completes
25 setting of the communication state, which has been transferred from the
first communication s t a t e c o n t r o l unit, the second communication state
control u n i t switches the operation state of the second board to the active
system.
3 0 11. A co.n~municationr elay control board comprising:
a f i r s t transmission control c i r c u i t that i s connected to an IF unit
by a f i r s t transmission path and controls usage of the first transnlission
path by the IF unit, the IF unit externally transmitting and receiving
communication data; and
a first comnlunication s t a t e control unit that manages a control
state of the colnmunication data that has passed through the f i r s t
transmission path, wherein
the communication relay control board is mounted as a redundant
5 board of another board that is connected to the IF unit by a second
transmission path,
when an operation state of the first transmission control c i r c u i t i s
an active system and detects i t s own f a u l t , the f i r s t transmission control
circuit
10 gives an instruction to the IF unit as to whether or not the
usage of the first transmission path i s allowed,
notifies the other board that the f a u l t i s detected and gives
an instruction to the IF unit whether o r not usage of the second
transmission path i s allowed, and
15 n o t i f i e s the first communication state control u n i t t h a t the
fault is detected,
in response to a notification from the first transmission control
circuit, the f i r s t communication state control unit evaluates a s t o whether
or not to switch i t s own operation state to a standby system, and
2 0 when the first communication state control u n i t evaluates t h a t its
own operation state i s switched to the standby system, the first
communication s t a t e control u n i t starts to take over the communication
state of the comnlunication d a t a , which has passed through t h e f i r s t
trans'mission path, to the other board.
2 5
12. The communication relay control board according to Claim 11,
wherein
when the operation state of the f i r s t board i s the active system and
the first transmission control c i r c u i t d e t e c t s a fault in the first board, the
30 first t r a n s n ~ i s s i o nc ontrol c i r c u i t evaluates as to whether or not the usage
of the f i r s t transmission path i s allowed according to existence o r absence
of a fault in the second board, and
the f i r s t transmission control circuit gives an instruction to the IF
unit based on an evaluation result.
13. The c o m ~ n u n i c a t i ore~l~a y control board according to Claim 12,
wherein
when the operation state of the first board i s switched, the f i r s t
5 communication state control unit determines a switch pattern f o r t h e first
transmission c i r c u i t to switch between whether o r not the usage of the
f i r s t transmission path i s allowed based on the switched operation slate
and sets the determined switch pattern in the f i r s t transmission control
circuit,
10 when the f i r s t transmission control c i r c u i t detects a fault in the
first board or receives, from the second transmission control c i r c u i t , a
notification t h a t a f a u l t i s detected, the f i r s t transmission control c i r c u i t
i d e n t i f i e s whether or not the usage of the f i r s t transmission path is
allowed according to the switch pattern t h a t has been set by the first
15 communication s t a t e control unit and a combination of existence or
absence of a fault in the f i r s t board and existence o r absence of a fault in
the second board, which is notified by the second board, and
the f i r s t transmission control c i r c u i t gives an instruction of a
result of the identification to the IF unit.
2 0
14. The communication relay control board according to any one of
Claims 11 to 13, wherein
when the f i r s t communication state control unit detects a fault,
which.cannot be detected by.the first transmission control c i r c u i t , in the
25 f i r s t board, the f i r s t com~nunication state control unit n o t i f i e s the f i r s t
transmission control c i r c u i t t h a t the f a u l t i s detected in the f i r s t board,
and
when the f i r s t transmission control c i r c u i t receives a notification
from the f i r s t comnlunication state control u n i t , the first transmissioll
30 control c i r c u i t detects the fault as a fault in the f i r s t board.