Line accommodation device and control method thereof

The present invention provides a line accommodation device comprising at least one first communication control unit for controlling information transmission/reception to/from a first communication system, at least one second communication control unit for controlling information transmission/reception to/from a second communication system using the first communication system as a communication medium and a route control unit for controlling the switching of an information transfer route between the first and second communication unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a line accommodation device, a control method and a control program thereof, and more particularly relates to a technology effective when applying them to a line accommodation technology for collecting a plurality of communication system stations and communication nodes or the like.

2. Description of the Related Art

In order to stably transmit/receive frames in many data network, networks utilizing a failure relief function possessed by a communication system, such as a synchronous optical network (SONET), a synchronous digital hierarchy (SDH), a wavelength division multiplexing (WDM) and the like are designed. In such a situation, a rating for realizing a failure relief function at a frame level while using SONET as a communication medium is the resilient packet ring (RPR). Thanks to the RPR rating, there becomes no need to build a redundancy configuration in order to relieve failures in SONET, SDH and WDM.

However, SONET or the like is still used as a communication medium, a network, such as SONET or the like must be built before an RPR is used.

As the prior art, there is IEEE 802.17 (RPR rating). In this rating, the detailed building method of an RPR network is not especially referred to. As indicated in the rating, in an RPR, it is important for RPR stations (hereinafter called “station”) are connected via two ring-shaped information transmission lines (ringlet) for transmitting information in mutually opposite directions. However, no attention is paid to how the stations are connected when SONET is used as a communication medium.

Judging from the disclosed contents of the rating, each station comprises one set of SONET interfaces (the combination of a clockwise SONET interface (SO1) and a counter-clockwise SONET interface (SO2)). If a station comprises a SONET interface, it is anticipated that a plurality of stations or a plurality of SONET interfaces is added/deleted to/from a line accommodation device accommodating the station (hereinafter called “shelf”). However, the configuration modification caused in such a shelf is not referred to.

Generally, a communication device capable of providing a large capacity of line services, such as a router, a transmission device or the like adopts a shelf structure. In this case, it is preferable to embody each communication service (such as a station, a SONET interface, etc,) in the form of a card (substrate) and to be able to freely insert/remove this card in/from the shelf.

If the RPR function is applied for such a usage, the contents disclosed of the above-mentioned rating is incomplete as it is. Particularly, a network must be built paying attention to the following points.(1) Disposing stations in a ring shape(2) Connecting a SONET interface in such a way not as to avoid wrong the East/West directions for a ring(3) Carefully connecting an optical fiber to a target ring if a plurality of RPRs is collected in the shelf

These setting (1) through (3) must be made for each station. As the combination of stations, not only the combination of stations in a shelf but also the combination of stations across a plurality of shelves are anticipated. In any case, attention must be paid so as to avoid a wrong connection.

In the RPR rating, the following alarms are issued if there is a wrong connection.(1) Mis-cable(2) Mis-cable connection(3) Keep-alive timeout(4) A regular report cannot be received from an adjacent station
However, these are not caused as long as there is no hardware failure, such as the wrong connection of east/west cables, a station failure or the like. Therefore, a method for detecting that a station is connected to an unintended RPR is not defined.

As to the failure relief of an RPR, if a station fails, it is clearly specified in the rating that the station should be disconnected. As the removal method, the steering/wrapping of the RPR is simply used. Therefore, when the station is broken and when the layer of a SONET, a SDH and a WDM fails, they are similarly relieved. In other words, even when a station is broken, the steering/wrapping of an RPR occurs.

Therefore, a network in which the RPR steering/wrapping occurs due to the failure of a station cannot activate a new RPR steering/wrapping until the station recovers from the failure. During this period, redundancy continues to be lost. In an RPR in which the length of one ring is assumed to be 2,000 km, there is a possibility that stations may be scattered a long distance away from each other. Therefore, it is not easy to switch the broken station. In this case, it takes a long time to recover the redundancy, that is, reliability of the station.

The above-mentioned problems of the prior art can be summarized as follows.(1) The addition of a station to an arbitrary ring is not assured.(2) The deletion of a station from an arbitrary ring is not assured.(3) The connection of stations to the same ring across a plurality of shelves is not assured.(4) When a station is broken, the station can be disconnected from the ring by RPR steering/wrapping. However, if another failure occurs by the influence, failure relief by RPR steering/wrapping cannot be realized.

Patent reference 1 discloses a transmission device for independently performing ring switching at a SONET/SDH network level and ring switching at a network level, such as an RPR or the like by providing a network signal processing means for switching a ring for each network signal using a synchronous signal obtained from a connection means connected to the SONET/SDH network. However, it does not recognize the above-mentioned technical problem in the case where a plurality of stations or SONET interfaces is installed in one shelf.Patent reference 1: Japanese Patent Application No. 2004-23620

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a technology capable of surely adding/deleting a second communication control means in a line accommodation device for accommodating the second communication control means connected to a second communication system using a first communication system as a medium.

It is another object of the present invention to provide a technology capable of assuring the accurate operation of a plurality of second communication control means belonging to each of a plurality of second communication systems in a line accommodation device for accommodating the second communication control means connected to a second communication system using a first communication system as a medium.

It is another object of the present invention to provide a technology capable of realizing the failure countermeasures of a second communication control means connected to a second communication system without degrading anti-failure function of the second communication system in a line accommodation device for accommodating the second communication control means connected to a second communication system using a first communication system as a medium.

The first aspect of the present invention is a line accommodation device. The line accommodation device comprises at least one first communication control unit for controlling the information transmission/reception to/from a first communication system, at least one second communication control unit for controlling the information transmission/reception to/from a second communication system using the first communication system as a communication medium and a route control unit for controlling the switching of an information transfer route between the first and second communication control unit.

The second aspect of the present invention is the control method of a line accommodation device comprising a first communication control unit for controlling the information transmission/reception to/from a first communication system and a second communication control unit for controlling the information transmission/reception to/from a second communication system using the first communication system as a communication medium. The control method comprises a first step of building the second communication system by connecting the first and second communication control unit via a route control unit for controlling the switching an information transfer route between the first and second communication control unit; and a second step of modifying the information transfer route when extending or removing the first and/or second communication control unit.

The third aspect of the present invention is a signal for carrying the control program of a configuration control device provided for a line accommodation device comprising a first communication control unit for controlling the information transmission/reception to/from a first communication system, a second communication control unit for controlling the information transmission/reception to/from a second communication system using the first communication system as a communication medium and a route control unit for controlling the switching of an information transfer route between the first and second communication control unit. The control program enables the configuration control device to realize: a function of enabling the route control unit to set the information transfer route for bypassing the failed second communication control unit when the second communication control unit fails or when it is disconnected from the line accommodation device; and a function of determining the adding position of the second communication control unit in the second communication system when adding the second communication control unit to the arbitrary second communication system.

The fourth aspect of the present invention is a signal for carrying a control program for controlling a second communication control unit in a line accommodation device comprising a first communication control unit for controlling the information transmission/reception to/from a first communication system, the second communication control unit for controlling the information transmission/reception to/from a second communication system using the first communication system as a communication medium and a route control unit for controlling the switching of an information transfer route between the first and second communication control unit. The control program enables the second communication control unit to realize: a function of adding identifying information to communication information transmitted to the second communication system; a function of detecting the identifying information added to the communication information; and a function of identifying each of the second communication systems, using the identifying information.

More specifically, since the RPR rating has no concept of registering a plurality of RPRs in one shelf (line accommodation device) or a plurality of stations (RPR station: the second communication control means) for example, when using a SONET/SDH as the first communication system and building an RPR in this SONET/SDH as the second communication system, the above-mentioned technical problems occur. In order to solve these problems, for example, the following methods are used.

Firstly, if a shelf accommodates a plurality of SDH interfaces and stations and the stations individually belong to the plurality of RPRs, a ring identification being a Ring-ID is attached to each RPR and RPRs related to the shelf are identified.

Secondly, the shelf comprises control logic for determining which SDH interface or station in the shelf should be connected according to a RING-ID. The control logic for this determination is executed by an intelligent card (configuration control means) provided in the shelf. An SDH interface or a station is connected according to the determination result without exchanging a line (frame). A shelf accommodating only one RPR needs no RING-ID.

Thirdly, a station comprises control logic for identifying each RPR by applying a RING-ID to a frame flowing through an RPR network in inter-station communication. Even when an RPR is connected across shelves in this way, stations in each shelf can surely prevent a failure, such as interference between different RPRs or the like by issuing an alarm, based on the Mismatch of the RING-ID, canceling the frame or the like if the frame is from an RPR with an expected RING-ID.

Fourthly, the array of stations belonging to each RPR can be managed in each shelf by using a RING-ID. When a failure occurs in each station or a service cannot be provided by removing a station from a shelf in this way, the station can be disconnected from the RPR by modifying the array of stations. In this case, since a station is not disconnected by an RPR function, the failure relief function of the RPR is not damaged, and accordingly, even when a failure occurs later, relief by the steering/wrapping function is possible.

As described above, in the present invention, for example, when building an RPR function using a SONET network, the RPR can be more simply used than the conventional method. Alternatively, it can be more easily used than the conventional method by adding a relief function which can be performed at a shelf level.

For example, in order to build an RPR network being the second communication system on a SONET being the first communication system, a plurality of station functions (the second communication control means) of the RPR network and two optical interfaces for SONET connection (the first communication control means) are needed. Since the number of stations in the RPR network is rated to be 255, 255 supports are needed in the RPR network. An arbitrary number of them can be used to build the RPR network. Each of the two optical interfaces takes charge of the East or West side.

The shelf comprises a station card for providing an RPR function, an optical interface card for connecting shelves and a line switching card or frame switching card (route control means) for connecting station cards or an optical interface card to a station card.

In order to build an RPR network, it becomes necessary to dispose a plurality of shelves on the RPR network. For that purpose, it is necessary to build a ring-shaped transmission line by connecting the shelves using an optical interface.

If a configuration for providing the function of an RPR network can be secured when building an RPR network using a plurality of shelves, each shelf can also support a plurality of RPR networks. In this case, in order to provide an RPR function, each RPR network requires one station card and two optical interfaces.

If a plurality of these configurations can be set in a shelf, one shelf can accommodate a plurality of RPR networks. In this case, the present invention can accommodate an arbitrary number of RPR networks in the shelf, using an identifier being a RING-ID.

In the function to automatically add/delete a station to a shelf, a RING-ID is needed to identify a target RPR network. If one shelf accommodate only one RPR network and a station is added/deleted, the present invention can be applied without any special RING-ID.

When adding a station, by also registering the RING-ID in the station, the intelligent card (configuration control means) in the shelf calculates the adding position (topology) of the station in the RPR network and modifies the design of the line switching method so as to connect the station to the RPR network. If the route control means performs frame switching, it modifies the frame switching setting. In this case, the setting is automatically modified according to a specific rule even if there is no instruction (such as an input from an operator) from a monitor device or a terminal to which the intelligent card is connected.

As in the case of station adding, a station can be deleted (disconnected) by modifying the connection setting of the route control means using an intelligent card.

In order to minimize the influence on the RPR network during the setting modification, in the case of the line switching method, a path-switch function is utilized. The path-switch function means to switch inputs from two directions by the switching operation of a receiving unit. Since using this function, a line to be used can be modified simply by throwing down a switch to the opposite direction after setting the line, the inputs can be instantaneously (such as within 50 milliseconds) switched. For example, if only one line is usually set, firstly, one line is added when additional operation is activated and the total number of lines becomes two. Then, a connection route can be switched by operating a path-switch to pass signals through the added line.

If the route control means adopts the frame switching method instead of the line switching method, the present invention modifies a route through which frames pass by adding specifying information to a routing table. In this case, when adding/deleting a line, valid/invalid information is attached in order to instantaneously modify the table instead of rewriting the table. If valid/invalid information is used, no mis-operation occurs even when a source address (SA) or a destination address (DA) is overlapped and registered in the routing table.

In order to determine the RPR network connection order of stations in the intelligent card, it is necessary to make a rule determining in what order stations should be registered in the RPR network. If this rule exists, according to the rule, it can be calculated in what position of the RPR network with the same RING-ID the station should be added. When deleting a station, it can be detected how the remaining stations should be connected after deleting it.

The present invention prepares an intelligent card in order to control the inside of a shelf. This intelligent card can also receive instructions from the outside, and set, for example, a RING-ID or the like in each card of the shelf according to the instructions of the operator. If a plurality of RING-IDs is supported, a RING-ID to use the shelf can be freely set by the instructions of the operator. Since the intelligent card can also calculate, it can collect alarms and statistic information from an optical interface card, a station card and the route control means and can also notify the operator or the monitor device of them.

A RING-ID can also be used when stations are accommodated across shelves, besides for the connection in the shelf. In this case, a RING-ID is set in a part of a specific RPR frame and it is transmitted to a station in an adjacent shelf. By comparing a RING-ID contained in the RPR frame with its own RING-ID in the station, the validity of a received frame can be determined. If they are the same, it can be determined that they are normal. If they are different, they are determined to be abnormal and a necessary process can be performed.

If an unexpected RING-ID is received from the adjacent station, it is detected that an unexpected station exists in the RPR network. In this case, a function to alarm against the fact if the RING-ID is not expected, is provided and the operator is urged to check the stations in the RPR network.

Furthermore, if it is desired that not only an alarm is issued but communication signals are also disconnected when an unexpected station exists in the RPR network, they can also be disconnected by the setting of the operator. In this way, data belonging to a specific RPR network can be prevented to leak to an unexpected RPR network due to the mis-connection of the optical fiber.

The RPR uses switching logic provided by the RPR function not only when signals are not transmitted due to the disconnection or failure of an optical fiber but also when the station fails. In the present invention, if a station falls in the state where the RPR function cannot be clearly provided due to the failure of the station or the like, the station is disconnected by controlling the route control means. Therefore, logic for detecting that a station falls in the state where the RPR function cannot be provided is installed in the intelligent card.

If a station falls in an abnormal state (such as failure, etc.), the station is disconnected from the RPR network and is re-disposed in a ring shape. The re-disposition is performed by controlling the route control means. In this case, an intelligent card that detects abnormality re-calculates the topology in another station which can avoid the station and sets a bypassing circuit for disconnecting it in the route control means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows an example of the configuration of the line accommodation device in the one preferred embodiment of the present invention.FIGS. 2 and 3show the detailed configuration of a part of the line accommodation device in the one preferred embodiment of the present invention.

As shown inFIG. 1, the shelf (line accommodation device)10of this preferred embodiment comprises an intelligent card (configuration control unit)20, a plurality of slots11, a route control unit (route control unit)50.

The slot11comprises a station (the second communication control unit)30and an optical interface (the first communication control unit)40which are attachable/detachable. The station30constitutes the communication node (RPR station) of an RPR (the second communication system) using an optical communication system (the first communication system), such as a SONET or the like, as a communication medium.

The optical interface40provides an interface connecting an optical communication system, such as a SONET or the like, and the station30.

The route control unit50controls an information transfer route between the station30and optical interface40which are installed in each slot11. This route control unit50can adopt either a line switching method or a frame switching method, as described later.

FIG. 2shows an example of the configuration of the intelligent card20.

The intelligent card20of this preferred embodiment comprises a microprocessor unit (MPU)21, main memory22, ROM23, an input/output interface24and a bus25.

The main memory22stores information, such as an operating system26, a shelf control program27, a card management table28and the like.

The MPU21manages the entire shelf10, as exemplified in the flowchart described later, by executing the operating system26and shelf control program27which are stored in the main memory22. The card management table28is used to execute the shelf control program.

The ROM23is composed of re-writable non-volatile storage medium and stores information, such as the operating system26, shelf control program27, card management table28and the like. When the intelligent card20is activated, the information is loaded from the ROM23to the main memory22.

The input/output interface24transmits/receives information to/from an external device via control signal lines12a,12b,12cand12d.

Specifically, the input/output interface24is connected to the station30, the route control unit50and the optical interface40via the control signal lines12a,12band12c.

The card management table28stores a slot ID28aand a Ring-ID28b, which are related. The slot ID28ais identifying information uniquely attached to each of the plurality of slots11. The Ring-ID28bis a RING-ID for identifying the RPR network70to which the station30installed to the slot11belongs, which is described later.

FIG. 3shows an example of the configuration of the station30. The station30of this preferred embodiment comprises a control unit31, a RING-ID storage unit39, a data transmitting/receiving unit32, a clockwise interface33, a counter-clockwise interface34, and generic framing procedure (GFP) framers35and36.

The control unit31performs the protocol control of the RPR and further performs the entire control of the station30by controlling the clockwise and counter-clockwise interfaces33and34under the management of a higher-order intelligent card20.

The data transmitting/receiving unit32controls the information transmission/reception between the station30and a user network80, such as an external LAN or the like.

The clockwise interface33controls the information transmission/reception between a ringlet37(ringlet0) constituting the RPR and the data transmitting/receiving unit32.

The counter-clockwise interface34controls the information transmission/reception between a ringlet38(ringlet1) constituting the RPR and the data transmitting/receiving unit32.

The GFP framers35and36converts an RPR frame into a general frame and maps it on a SONET frame.

The RING-ID storage unit39stores RING-IDs attached to an RPR to which the station belongs. This RING-ID is provided by the intelligent card20.

In the following description, the station30and optical interface40are referenced as an SSn and an OPTSn, respectively, as required (n: a natural number).

In the free slot11of the shelf10, an optical interface40for connecting this station30to an RPR network70built on the SONET is installed, as necessary. The station30and optical interface40installed in the slot11can transmit/receive information via the route control unit50.

Specifically, each of the station30and optical interface40installed in the slot11is connected to the route control unit50via a main signal line13.

The optical interface40is connected to the SONET being the communication medium of the RPR network via an optical fiber41.

The station30is connected to a user network80via a communication cable81.

In this preferred embodiment, if a plurality of stations30installed in the shelf10is independently connected to different RPR networks70, a unique Ring-ID28bis attached to each RPR network70.

The RING-ID is registered in the shelf10from a monitor device60to the intelligent card20. In this case, the card management table28determines which optical interface40should be used by which RING-ID.

Specifically, in the slot ID28aof the card management table28, the identifying information of the station30or optical interface40installed in the slot11is set, and the RING-ID attached to the station30or optical interface40is set in the Ring-ID28b.

Therefore, in each of the corresponding station30and optical interface40, the same RING-ID is set.

InFIG. 4, the monitor device60sets a RING-ID “1” as an example. In this case, the optical interface40is registered in the RPR network using OPTS1and OPTS2for the east and west sides, respectively. When registering the RING-ID in the shelf10, the slot position (slot ID28a) of the optical interface40must be clear. However, there is no problem regardless of whether it is installed. There is also no problem even if the station30installed or if it is not under the control of the intelligent card20.

If the station30is added to the shelf10after the RING-ID is registered, the intelligent card20controls the route control unit50, according to the logic shown in the flowchart ofFIG. 5.

When the intelligent card20automatically registers the station30, the following two items become important.

(Item 1) The handling of the RING-ID for indicating the RPR network70to which the station30is added

(Item 2) The disposing method in the shelf10of the station30belonging to the same RING-ID (RPR network70)

As to item 1, since it is assumed that a plurality of RPRs is developed in the same shelf10, it is needed to distinguish the RPRs. If only one RPR is handled, no RING-ID is needed. There is no problem even if RPRs are unconditionally added against the optical interface40. Alternatively, the RING-ID can be provided with a default value (for example, RING-ID=0) so that the user of the RPR may not aware of the RING-ID (See flowchart inFIG. 6mentioned below).

Since the essential purpose is to accommodate a plurality of RPRs in the same shelf10, it is important to dispose stations30with the RING-ID according to a determined rule (the disposition rule in item 2). As the disposition rule of stations30in the shelf10, the following three rules can be considered.

Rule A: Array the stations30in ascending order of the installed slot number.

Rule B: Array the stations30in clockwise order of the ring.

Rule C: Array the stations30in order connected to the RPR.

In this preferred embodiment, Rules A and B are used. Alternatively, rule C can be used.

By arraying the stations30in the shelf10according to a specific rule in this way, stations30with the same RING-ID can be added to the RPR simply by calculating their number in the intelligent card20, without the help of the operator via the monitor device60.

Specifically, the adding operation of the station30is described below with reference toFIGS. 5,6,7and8. When adding a station30, firstly, the station30is registered in an arbitrary slot (step101), and a RING-ID is assigned to the station30(step102).

Then, it is determined whether another station30with the same RING-ID exists in the shelf10(step103).

If it does not exist, the east side connection destination is connected to the east side optical interface40(FSA1′) (step104), and the west side connection destination is connected to the west side optical interface40(FSA2′)(step105).

FIG. 7shows the transition of the connection route in the route control unit50in steps104and105.

If in step103it is determined that it exists, the array of the slot11is lined up clockwise to the RPR network70(step106).

Then, the slot numbers of stations to the right and left of the newly registered slot11(provided with the station) are checked (if there is no station30, the number of the optical interface40is checked) (step107).

Then, it is determined whether the east side connection must be modified (step108). If necessary, a connection between the east side connection destination and the east side of the target station30is added (FSA1) (step113).

Furthermore, it is determined whether the west side connection must be modified (step109) If necessary, a connection between the west side connection destination and the west side of the target station30is added (FSA2) (step114).

Then, it is determined whether a connection is added to the east side (step110). If it is added, the old connection on the east side is deleted (FSA3) (step115).

Similarly, it is determined whether a connection is added to the west side (step111). If it is added, the old connection on the west side is deleted (FSA4) (step116).

FIG. 8shows the transition of the connection route in the route control unit50in steps106through116.

After these processes, the added station30transmits/receives RPR information to/from an adjacent station, using the registered RING-ID (step112). Since in the logic of the flowchart shown inFIG. 5, the route control unit50simply relates the station30to the order of the optical interface40, according to the disposition logic of the station30, the logic of the flowchart is not affected by the optical interface40or station30with a different RING-ID. Therefore, as shown inFIG. 9, each station30can be connected to a different RPR network70by controlling the route control unit50using the intelligent card20.

One example of the preparation process in the case where no RING-ID exists is described with reference to the flowchart shown inFIG. 6.

Firstly, it is determined whether a RING-ID exists (step201). If it exists, the process is terminated. If in step201it does not exist, it is determined whether two optical interfaces40are not connected to the route control unit50(step202). If they exist, it is specified that RING-ID=1 (default value) and the support state of the RING-ID is generated using the optical interfaces not connected to the route control unit50(step203). Specifically, it is registered in the card management table28.

If in step202, no optical interfaces40unconnected to the route control unit50exist, the process is suspended since there are no optical interfaces to be connected to the RPR network70(step204).

The logic for deleting a station30is structured as shown by the flowchart inFIG. 10. When deleting a station30, the station30is disconnected from the RPR network70by directly connecting the east and west sides of the target station30.

FIGS. 11,12and13show the configuration of the shelf10before deletion, the transition of the connection route in the route control unit50during the deletion process of the station30and the configuration of the shelf10after deletion, respectively.

As exemplified inFIG. 10, in the deletion process of a station30, firstly, the switching destination of the cyclic frame of the target station is checked on each of the east and west sides (step301).

Then, it is determined whether the target station30is the last station belonging to the same RPR network70in the shelf10(step302).

If it is determined that the target station30is not the last station30, it is further determined whether a connection destination exists on both of the east and west sides (step303). If they are not detected, it is determined that the station30cannot be deleted (step307).

If in the step303, it is determined that a connection destination exists on both of the east and west sides, the connection route (FSD1inFIG. 12) of the route control unit50is set in such a way that the east and west side connection destination stations30can be connected (step304).

Then, the east side connection route (FSD2inFIG. 12) of the station30to be deleted is deleted (step305), and the west side connection route (FSD3inFIG. 12) of the station30to be deleted is deleted (step306).

If in step302the target station30is the last station30, steps305and306are executed, and the east and west side connection routes are deleted.

In either adding or deleting a station30and in either the line switching method or frame switching method, line disconnection time can be shortened to a level meeting the requirements of the RPR network70(for example, within 50 milliseconds) by the control method of the route control unit described later.

Specifically, in the case of the SONET/SDH method, a line can be switched within 50 milliseconds in the route control unit50by configuring a “path-switch”, which is described later. In the case of the frame switching method, a frame can be switched within 50 milliseconds by devising the setting of the routing table53, as described later.

Table 1 exemplifies the combination of connection routes inside the route control unit50in the above-mentioned addition/deletion of a station30.

When connecting stations30across a plurality of shelves10, the Ring-ID28b(RING-ID) is used. In this way, it can be checked whether the transmitting source of information from an adjacent shelf10is a station30with an expected RING-ID, more strictly than the existing error detection methods, such as “mis-cable”, “keep-alive” or the like.

For example, it is assumed that there is an RPR network70accommodating six stations30in three shelves10, as shown inFIG. 14. All the stations30in all the shelves10are managed on the condition of “RING-ID=1”. In this case, an RPR control frame containing an RPR protocol which is transmitted/received in the optical interface40exists. If there is a free band in it, an IDLE-Frame exists as a frame to be compulsorily transmitted.

By embedding a Ring-ID in an IDLE-Frame transmitted/received between stations30or shelves10, each station30or shelf10can know the Ring-ID of an adjacent station30when receiving the IDLE-Frame. If the received Ring-ID differs from the transmitting Ring-ID, an alarm is issued. Alternatively, the validity of the received data is nullified and discarded.

FIG. 15is a flowchart specifically exemplifying the process of each station30when transmitting/receiving a frame on the RPR network70.FIG. 16shows an example of the structure of the IDLE-frame.

As shown in the upper section ofFIG. 16, an idle frame71rated by the RPR rating includes a frame life72, a base control73, a transmitting source MAC address74, a reservation area75and a frame check sequence76.

The frame life72is eight bits long and indicates the life of the idle frame71in the RPR network70. The base control73is eight bits long and indicates a class by which the idle frame is transmitted. The transmitting source MAC address74is 48 bits long, and indicates the MAC address of the transmitting source station30generating the idle frame71. The reservation area75is 32 bits long, is provided for future use and is usually occupied by “0” entirely.

In this preferred embodiment, as shown in the lower section ofFIG. 16, a ring ID75ais stored using the former 16 bits of this reservation area75. The latter 16 bits are left as the remaining reservation area75b.

As described above, in this preferred embodiment, the ring ID75athat is stored in the idle frame71and is transmitted/received between stations30is used to determine the validity of a frame when receiving the frame.

The station30waits for the reception of the idle frame71containing the ring ID75afor a specific period. Simultaneously, it transmits the idle frame71containing the ring ID75aof an RPR network70to which the station30belongs as the transmitting side. When receiving no ring ID75afor a specific period, like the keep-alive essential to an RPR, determines that no adjacent station30is seen, and detects a Ring-Id-Mismatch. When detecting no Ring-Id-Mismatch, it accepts the received frame as correct one. The behaviors of the station30while detecting the Ring-ID-Mismatch can be set by the intelligent card20. In this case, one of the two operations of an operation to discard the frame and one to accept the frame can be set. The station30discards or accepts the frame according to the setting, and the process proceeds to a subsequent step. The monitor logic of the Ring-ID is operated as long as the station30belongs to the RPR network70. When the station30is disconnected from the RPR network70, the monitor logic is terminated.

Specifically, as exemplified by the flowchart in theFIG. 15, firstly, the station30refers to a RING-ID storage unit39and determines whether a Ring-ID is registered in the station30(step401). If it is registered, it is determined whether there is a failure at an optical communication medium level (that is, in the SONET being a communication medium) (step402).

If no failure is detected in an optical medium, the station30waits for the reception of the RPR control frame (in this preferred embodiment, idle frame71) (step403), and also transmits the idle frame71containing the ring ID75a(step404).

The station30determines whether the waiting time of the idle frame71has elapsed or the idle frame71has received (step405). If the station30has received the idle frame71within the waiting time, it determines whether the ring ID75astored in the received idle frame71matches the transmitted value of its own station (that is, the Ring-ID28bof the RPR network70to which its own station belongs) (step406). If they are matched, the station30accepts the received idle frame71and applies a prescribed process (step407), and the process returns to the step401.

If in the step405, the waiting time has elapsed, the station30notifies the intelligent card20of the detection of the RING-ID-Mismatch (step409). Then, the station30determines whether the received frame should be nullified, according to an instruction from the intelligent card20(step410). If it is nullified, the station30discards the received frame (step411) and the process returns to the step401. If in step410the received frame is validated, the process is branched into the step407.

If in the step402, a failure is detected in the optical medium, the station30notifies the intelligent card20of the detection of optical failure (step408), and then the process returns to the step401.

If a plurality of stations30exists in a specific Ring-ID in the same shelf10and if the station falls into no service-available state due to a failure, disconnection or the like, the station30is disconnected by controlling the route control unit50using the intelligent card20. In this way, even when a failure requiring the replacement of a station30occurs, the failed station30can be disconnected. Therefore, time the RPR switching function is affected can be minimized.

One specific example of the logic is shown by the flowchart inFIG. 17. The disconnecting operation can be realized by setting a connection route for bypassing a station30to be disconnected in the route control unit50. This disconnection process of a station30is similar to that of adding/deleting a station30. As the setting method of the bypassing connection route in the route control unit50, in the case of the line switching method, the path-switch switching function is used. In the case of frame switching method, the switching can be realized by devising the setting information of a frame switching routing table53.

As an example, a case where in the connecting configuration of a plurality of shelves10exemplified inFIG. 18, a failure occurs in a station30(SS21) is studied. For the reason of this failure, the station (SS21) is disconnected from the RPR network70in which Ring-ID=1 by controlling the route control unit50as shown inFIG. 19.

Specifically, as exemplified by the flowchart inFIG. 17, firstly, it is determined whether a Ring ID is registered in the station30(step501). If it is registered, it is determined whether a failure occurs in the station30(step502).

If a failure occurs in the station30, a disconnecting operation is activated (step503), and the east side connection destination and west side connection destination of the station30to be disconnected are connected (step504).

If in the step502, no failure occurs in the station30, it is determined whether the station30is disconnected (step505). If the station30is disconnected, a reconnecting operation is activated (step506), and the connection set in step504is deleted (step507).

Next, referringFIG. 20A through 20C, a case where a connection is modified by SONET/SDH line switching is studied. In the case of the line switching method, the route control unit50comprises a line switching unit51as a route control function. This line switching unit51comprises a path51aand a path-switch function composed of path switching units51band51cfor instantaneously switching this path51a.

Signals passes through a route indicated by a line (PT1) before disconnection, as shown inFIG. 20A. In order to disconnect the station30(SS21) in this state, as shown inFIG. 20B, a line (PT2) is newly established. Then, the line (PT1) is switched to the line (PT2). In this way, the station30(SS21) is disconnected.

If the station30(SS21) is recovered from the failure by substrate replacement or the like, as shown inFIG. 20C, the original route using the line (PT1) is restored by connecting back the path switching units51band51cto the line (PT1) switched and unused without being deleted.

However, if the connection between the station30and the optical interface40is modified by frame switching in the route control unit50, as shown inFIG. 21, the route control unit50comprises a frame switching unit52. This frame switching unit52comprises a plurality of connection ports to each of which the station30and the optical interface40are connected, which is not shown inFIG. 21. Using the routing table53exemplified inFIG. 22A, a connection route set between the connection ports is controlled. Specifically, in the routing table53, a transmitting source address53aand a destination address53bare set for each connection route.

The transmitting source address53aindicates the address of the connection port of the frame switching unit52to which the transmitting source station30or optical interface40is connected.

The destination address53bindicates the address of the connection port of the frame switching unit52to which the destination station30or optical interface40is connected.

Furthermore, in this preferred embodiment, a freeze flag53cis set for each connection route defined by the routing table53.

This freeze flag53cis set to prevent the route from being forgot from the routing table53while bypassing a specific route (connection route) when controlling the route using the routing table53. Specifically, “YES” and “NO” are set in the table entry of a route that must be restored and those other than the route, respectively.

In the initial setting state shown inFIG. 22A, in the frame switching unit52, a connection port (a22a) to which OPTS22is connected and a connection port (a2w) to which the west side of SS22is connected are bi-directionally connected. A connection port (a2e) to which the east side of SS22is connected and a connection port (a1w) on the west side of SS21are bi-directionally connected. A connection port (a21a) to which OPTS21is connected and a connection port (a1e) to which the west side of SS22is connected are bi-directionally connected.

In this way, a plurality of SS22and SS21are connected to OPTS22and OPTS21, respectively, in a loop. If in the normal state set as shown inFIG. 22A, one station30(SS21) is disconnected, as shown inFIG. 22B, a bypassing route for bi-directionally connecting the connection ports (a21a) and (a2e) is newly established in the routing table53, and a freeze flag53c(in this case, “YES”) is set in a table entry corresponding to the old bypassed route.

When the station30(SS21) is restored, as shown inFIG. 22C, the table entry added for bypassing is deleted from the routing table53and the setting of the freeze flag53cof the table entry in the old route is released (“NO”), thereby restoring the station30(SS21) to a normal state.

Even when the station30(SS21) is being disconnected, the intelligent card20can uniquely calculate how he connection route should be modified in the route control unit50when disconnecting it since for a rule on the positional relationship (such as clockwise disposition, etc.) among stations30in the RPR network70is determined.

Even if a part of the stations30is disconnected from the RPR network70, the ring state of the transmission line of the RPR network70is maintained. Therefore, although remedies by the anti-failure function of the RPR itself is temporarily applied while being disconnected, the remedies of the RPR itself are released when the RPR network70is restored to a ring state.

Therefore, when a multi-failure occurs, firstly countermeasures, such as the disconnection of the station30by the route control of the route control unit50functions. If a failure further occurs in the station30or the like in that state, the essential failure countermeasures of the RPR function. As a result, tolerance to a multi-failure can be improved compared with the prior art.

As a factor for disconnecting the station30, the failure of a circuit substrate constituting the station30(including keep-alive failure), the falling of the station30off the slot11, the occurrence of Ring ID-Mismatch or the like can be considered.

As described above, according to this preferred embodiment, if a plurality of stations belonging to the same or different RPR networks70is installed in a shelf10, a station30added/deleted to/from the shelf can be automatically registered/deleted, respectively, in/from an RPR network70.

Even if a plurality of shelves10each provided with a plurality of stations30is connected to the RPR network70, accurate communication without interference among different RPR networks70can be realized by applying appropriate anti-error measures, such as the issuance of an alarm for a mis-connection or the like when connecting a station30to a wrong RPR network70, using a Ring-ID set in the RING-ID storage unit39of the station30, from the intelligent card20.

Furthermore, since the intelligent card20monitors the operating condition of the station30and optical interface40, the intelligent card20can automatically disconnect the station30by controlling the route control unit50if the station30must be disconnected from the RPR network70for the reason of the failure of the station30or the like. If the failure of the station30is recovered by replacing a circuit substrate constituting the station30or the like, the station30can be automatically restored to its original state by controlling the route control unit50.

According to the present invention, the second communication control means can be accurately added/deleted to/from a line accommodation device for accommodating the second communication control means connected to the second communication system using the first communication system as a medium.

In a line accommodation device for accommodating the second communication control means connected to the second communication system using the first communication system as a medium, the accurate communicating operation of a plurality of the second communication control means belonging to each of a plurality of the second communication systems can be assured.

In a line accommodation device for accommodating the second communication control means connected to the second communication system using the first communication system as a medium, anti-failure measures can be applied to the second communication control means connected to the second communication system, without degrading the anti-failure performance of the second communication system.

The application of the present invention is not limited to the above-mentioned preferred embodiments, and the present invention can also variably modified as long as the subject matter of the present invention is not deviated.