ATM communication system, process migration method in the ATM communication system, and handover processing method

Abstract

An ATM communication system has a connection setting section for controlling a plurality of ATM switches to set an n:n bidirectional ATM connection having n terminals of a plurality of constituent terminals as terminal points and using the VPI/VCI for identifying the n terminal points, and a process ID allocating section for allocating an MID as a process ID to a plurality of processes, executed by the n terminals for sending a message to the bidirectional ATM connection. The ATM communication system migrates a process executed on an arbitrary terminal to another terminal while keeping the process ID allocated to the processes. Where a dead-lock occurs due to that a process becomes a sleep state for the reason of that the bandwidth of a physical link is insufficient for executing in parallel the processes on the ATM communication system, the bandwidth of the physical link that a sleeping process occupies is intercepted to avoid a CAC dead-lock.

Claims

What is claimed is:

1. An ATM communication system comprising:

a plurality of ATM switches; and

a plurality of terminals connected to each other through said plurality of ATM switches,

wherein, since a bandwidth of connection required to be set exceeds a remaining bandwidth of at least one physical link between said ATM switches or between said ATM switches and said terminals and/or a required computational resource for the process is assigned to another process, when dead-lock occurs and a process executed by one of said plurality of terminals becomes blocked, a control procedure executed by said ATM communication system intercepts a bandwidth of at least one physical link reserved by a group of blocked processes to allocate it to a bandwidth required by a process which requires the connection setting.

2. An ATM communication system comprising:

a plurality of ATM switches;

a plurality of terminals connected to each other through said plurality of ATM switches;

connection setting means for controlling said plurality of ATM switches to set an n:n bi-directional ATM connection having n terminals of said plurality of terminals as terminal points, and the same connection identifier for identifying said n terminal points;

process identifier allocating means for allocating, to a plurality of processes, executed by said n terminals, for sending a message to said bi-directional ATM connection, a process identifier for identifying the processes; and

migrating means for the migrating process executed on an arbitrary terminal of said n terminals to another terminal of said n terminals while keeping the process identifier allocated to the process by said process identifier allocating means,

wherein the process sends a message constituted by a single cell including the identifier of the terminal in which the process is executed and the process identifier allocated to the process to said bi-directional ATM connection at predetermined time intervals, when the message constituted by a single cell including the process identifier allocated to the process is received, holds the contents of the message, and forms and holds a table of the process identifier allocated to the process connected to said bi-directional ATM connection.

3. An ATM communication system according to claim 2, wherein a process group for managing resources in the processes respectively have a global unique resource identifier for identifying resources, and when said ATM communication system is powered on, a master resource process for allocating the resources to be managed by the processes to the process group identifies, by the process identifier, a process which manages a resource allocated when said ATM communication system is powered on.

4. An ATM communication system according to claim 3, wherein the process group for managing resources manages the bandwidth of at least one predetermined physical link between at least said ATM switches or between said ATM switches and said terminals, having a global resource identifier to identify said physical links, and identifies a process in which a master resource process which allocates physical links to be managed by the processes to the process group when said ATM communication system is activated manages a resource allocated by the process identifier when said ATM communication system is activated, and

since the bandwidth of a connection required to be set by a process executed in one of said plurality of terminals exceeds the remaining bandwidth of at least one physical link between said ATM switches or between said ATM switches and said terminals, when it is cleared by communication between the resource process groups that dead-lock occurs when the process becomes a sleep state, a process executed in said ATM communication system intercepts a bandwidth of at least one physical link assured by a group of sleeping processes, and allocates a bandwidth required by a process in which one of said resource process group requires the connection setting.

5. An ATM communication system comprising:

a plurality of ATM switches;

a plurality of terminals connected to each other through said ATM switches;

connection setting means for controlling said plurality of ATM stitches to set an n:n bi-directional ATM connection having n terminals of said plurality of terminals as n terminal points and using the same VPI and VCI of a cell header serving as a connection identifier for identifying the n terminal points;

process identifier allocating means for allocating, to a plurality of processes for sending a message to said bi-directional ATM connection, a multiplex identifier of an AAL3/4 as a process identifier for identifying the processes; and

migrating means for migrating the process executed on an arbitrary terminal of said n terminals to another terminal of said n terminals while the process identifier allocated to said processes by said process identifier allocating means,

wherein the process sends a message constituted by a single cell including the identifier of the terminal in which the process is executed and the process identifier allocated to the process to said bi-directional ATM connection at predetermined time intervals, when the message constituted by a single cell including the process identifier allocated to the process is received, holds the contents of the message, and forms and holds a table of the process identifier allocated to the process connected to said bi-directional ATM connection.

6. An ATM communication system according to claim 5, wherein a process group for managing resources in the processes respectively have a global unique resource identifier for identifying resources, and when said ATM communication system is activated, a master resource process for allocating the resources to be managed by the processes to the process group identifies, by the process identifier, a process which manages a resource allocated when said ATM communication system is activated.

7. An ATM communication system according to claim 6, wherein the process group for managing resources manages the bandwidth of at least one predetermined physical link between at least said ATM switches or between said ATM switches and said terminals, having a global resource identifier to identify said physical links, and identifies a process in which a master resource process which allocates physical links to be managed by the processes to the process group when said ATM communication system is activated manages a resource allocated by the process identifier when said ATM communication system is activated, and

since the bandwidth of a connection required to be set by a process executed in one of said plurality of terminals exceeds a remaining bandwidth of at least one physical link between said ATM switches or between said ATM switches and said terminals, when it is cleared by communication between the resource process groups that dead-lock occurs when the process is slept, a process executed in said ATM communication system intercepts a bandwidth of at least one physical link assured by the slept process group, and allocates it to a bandwidth required by a process in which one of said resource process group requires the connection setting.

8. An ATM communication system comprising:

a plurality of ATM switches;

a plurality of terminals connected to each other through said ATM switches;

connection setting means for controlling said plurality of ATM switches to set an n:n bi-directional ATM connection having n terminals of said plurality of terminals as n terminal points and using the same VPI of a cell header serving as a connection identifier for identifying the n terminal points;

process identifier allocating means for allocating, to a plurality of processes for sending a message to said bi-directional ATM connection, a VCI of a cell header serving as a process identifier for identifying the processes; and

migrating means for migrating the process executed on an arbitrary terminal of said n terminals to another terminal of said n terminals while the process identifier allocated to said processes by said process identifier allocating means,

wherein the process sends a message constituted by a single cell including the identifier of the terminal in which the process is executed and the process identifier allocated to the process to said bi-directional ATM connection at predetermined time intervals, when the message constituted by a single cell including the process identifier allocated to the process is received, holds the contents of the message, and forms and holds a table of the process identifier allocated to the process connected to said bi-directional ATM connection.

9. An ATM communication system according to claim 8, wherein a process group for managing resources in the processes respectively have a global unique resource identifier for identifying resources, and when said ATM communication system is powered on, a master resource process for allocating the resources to be managed by the processes to the process group identifies, by the process identifier, a process which manages a resource allocated when said ATM communication system is powered on.

10. An ATM communication system according to claim 9, wherein the process group for managing resources manages the bandwidth of at least one predetermined physical link between at least said ATM switches or between said ATM switches and said terminals, having a global resource identifier to identify said physical links, and identifies a process in which a master resource process which allocates physical links to be managed by the processes to the process group when said ATM communication system is activated manages a resource allocated by the process identifier when said ATM communication system is activated, and

since the bandwidth of a connection required to be set by a process executed in one of said plurality of terminals exceeds the remaining bandwidth of at least one physical link between said ATM switches or between said ATM switches and said terminals, when it is cleared by communication between the resource process groups that dead-lock occurs when the process becomes a sleep state, a process executed in said ATM communication system intercepts a bandwidth of at least one physical link assured by a group of sleeping processes, and allocates a bandwidth required by a process in which one of said resource process group requires the connection setting.

11. A communication system comprising:

a plurality of switches;

a plurality of terminals connected to each other through said plurality of switches;

a detection unit for detecting that a process executed by one of said plurality of terminals becomes blocked by a dead-lock since a required bandwidth for a connection to be set exceeds a remaining bandwidth of a physical link between said plurality of switches or between one of said plurality of switches and one of said plurality of terminals and/or a required computational resource for the process is assigned to another process; and

a bandwidth allocation unit for intercepting, when the detection unit detects the deadlock, a bandwidth of the physical link reserved by one or more blocked processes to allocate the required bandwidth to the connection.

12. A bandwidth allocating method in a communication system having a plurality of switches which connect a plurality of terminals, the method comprising the steps of:

detecting that a process executed by one of said plurality of terminals becomes blocked by a dead-lock since a required bandwidth for a connection to be set exceeds a remaining bandwidth of a physical link between said plurality of switches or between one of said plurality of terminals and one of said plurality of terminals and/or a required computational resource for the process is assigned to another process; and

intercepting, when the detecting step detects the deadlock, a bandwidth of the physical link reserved by one or more blocked processes to allocate the required bandwidth to the connection.

Description

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a communication system, including a plurality of terminals, for performing communication among these terminals and, more particularly, to an ATM communication system using an ATM (Asynchronous Transfer Mode) and a process migration method in the ATM communication system.

2. Description of the Related Art

ATM (Asynchronous Transfer Mode) has attracted attention as a technique aimed at increasing the speed of transmission/switching. ATM is a technique in which all pieces of information are carried by short fixed-length packets called cells to be transferred by packaging hardware for packet exchange, thereby making it easy to transmit/switch information at a high speed.

ATM is regarded as a "promised solution" of a future B-ISDN (Broadband aspects of Integrated Services Digital Network). For this reason, study and development for applying the ATM technique to various communication systems have been actively performed in recent years. For example, a so-called ATM-LAN in which the ATM technique is applied to not only a public network operated by a carrier but also a network, i.e., local area network (LAN), using a restricted area, e.g., one floor of an office; to improve inter-operability with a public network, or a method of applying the ATM technique to a so-called CATV network which presents communication services to a restricted area being developed.

In the ATM communication system using the ATM technique, before communication, a connection is established between terminals that will communicate with each other. When the terminals communicate with each other, a cell is sent to the communication system and, the identifier of the connection is written in the header portion of the cell. The communication system refers to the header portion of the cell when transferring the cell along the connection to which the cell belongs, thereby transferring the cell to a desired terminal. In the ITU-T standards, the identifier of the connection in an ATM layer is called a VPI/VCI.

In this manner, in the ATM communication system, communication is performed by using a connection. For this reason, an ATM switch included in the ATM communication system has a routing tag table for holding information indicating a specific output port to which a cell belonging the connection set on each input port is transferred and the value of a new VPI/VCI used when the cell belonging to the connection is sent from the ATM switch. Connection setting in the ATM layer is performed by setting the routing tag table on the ATM switch through which the connection passes to be a desired value.

The ATM communication system performs communication by setting a connection in advance as described above. Desired communication quality can be advantageously given to each terminal by allocating the bandwidth of each physical link to the connection in advance. However, the ATM communication system has the following problem.

A conventional ATM communication system cannot efficiently perform a multi-media application due to the following problem.

FIG. 18 shows the arrangement of an ATM-LAN serving as an example used to explain the problem. This ATM-LAN is constituted such that terminals #1 to #5 (P021 to P025) are connected to each other by hubs #1 to #5 (P011 to P015). Physical link pairs P031 to P039 are arranged to connect the hubs and terminals to each other in order to realize full duplex communication. Physical links such as optical fibers or UTPs provide unidirectional information transfer, and are used as pairs.

In addition, the terminal #1 (P021) has a file #1 (P041), the terminal #2 (P022) has a file #2 (P042), and, similarly, the terminal #5 (P025) has a file #5 (P045).

In a conventional LAN such as an ethernet, a communication bandwidth on a coaxial cable is shared by connections. However, in an ATM-LAN, CAC (Connection Admission Control) which is unique to the ATM-LAN is performed before communication is started, a communication bandwidth is exclusively allocated to each connection. For this reason, in the conventional LAN, a communication bandwidth allocated to a connection changes due to the operation of other processes. In the ATM-LAN, since communication bandwidths allocated to connections do not change due to the operation of other processes, communication which assures QoS such as to read data from a file at a constant speed can be performed. On the other hand, in a conventional LAN, a process using the LAN can always send a message. In contrast to this, in the ATM-LAN, when communication bandwidths are not allocated by the CAC, communication cannot be performed. For this reason, when executing applications using communication bandwidths and a resources such as files, when the applications distributed on the ATM-LAN are executed, the following problem is posed.

This problem will be described with reference to the ATM-LAN shown in FIG. 18.

A process A executed on the terminal #1 (P021) reserves the file #1 (P041) and transfers it to the terminal #3 (P023). In addition, a process B executed on the terminal #2 (P022) refers to the contents of the file #1. When the processes A and B are executed simultaneously, the following may occur.

The process A opens the file #1 (P041) first. On the other hand, the process B obtains all the communication bandwidth on physical links P036 and P037. In this state, the process A tries to obtain a route to the file #3 (P043) and the communication bandwidths on the physical links P036, P033, P034, and P038. However, at this time, since all the communication bandwidths of the physical link P036 has been reserved by the process B. The process A fails to obtain the communication bandwidth. The process B tries to open the file #1 (P041). However, since the file #1 (P041) has been opened by the process A, the process B fails to open the file. When the processes A and B are blocked (i.e., put to sleep) in this state, a dead-lock state occurs.

Dead-lock of such a type occurs due to a conflict of the usage requests of the processes A and B between the file #1 (P041) and the communication bandwidth on the physical link P036. More specifically, the dead-lock of such a type occurs because the CAC exclusively gives the communication bandwidth to a certain process, and is called CAC dead-lock. When communication bandwidths are allocated by Q. 2931, each process cannot recognize that the dead-lock state is caused by conflicts on the communication bandwidth on the physical link P036, and the CAC dead-lock cannot be canceled.

In a general communication system, due to a defective terminal, it may be desired to migrate a process executed on the terminal to another terminal. Such migration of a process from one terminal to another terminal is generally called process migration. In the conventional ATM communication system, this process migration is performed by the following procedure.

FIG. 31 shows a procedure of process migration on the conventional ATM communication system. In this procedure shown in FIG. 31, terminals #1 (X041), #2 (X042), . . . , #n (X04n) which are connected to each other by the ATM communication system. In the conventional ATM communication system, a Q. 2931 terminated portion X01 which terminates Q. 2931 protocol for setting connections is present, a signaling VC#i (X02i) is set between the Q. 2931 terminated portion X01 and the terminals X04i. The signaling VC#i (X02i) is used to cause each terminal to specify the terminal of a callee or destination for the Q. 2931 terminated portion X01. The Q. 2931 terminated portion X01 sets a connection between a terminal which requests connection setting and a terminal specified by the connection setting request to use the connection for communication between the terminals. Although an ATM switch and physical links constituting the ATM communication system are omitted in FIG. 31 to avoid cumbersome illustration, it is considered that the ATM switch and physical links are present at a portion where the above VCs are set.

In the example shown in FIG. 31, a process #1 (X051) is executed on the terminal # (X041), and a process #2 (X052) is executed on the terminal #2 (X042). The process #1 (X051) communicates with the process #2 (X052) through a connection X03. Later, the process #2 (X052) running on the terminal #2 (X042) is migrated to the terminal #n (X04n).

FIG. 32 shows a state after the migration. In order to perform the communication between the process #1 (X051) and the process #2 (X052), a new connection Y02 is set between the terminal #1 (X041) and the terminal #n (X04n). A connection Y03 set to perform the communication between these processes before migration is released. In order to migrate the process #2 (X052) from the terminal #2 (X042) to the terminal #n (X04n), a connection Y01 is set between the terminal #2 (X042) and the terminal #n (X04n). Upon completion of migration, the connection Y01 is released.

FIG. 33 shows a migration procedure performed in a conventional ATM communication system to shift the state shown in FIG. 31 to the state shown in FIG. 32.

When the terminal #2 (X042) tries to migrate the process #2 (X052) executed on the terminal #2 (X042), the terminal #2 (X042) requests the Q. 2931 terminated portion X01 to set the connection Y01 (step Z01). When the Q. 2931 terminated portion X01 receives the connection setting request, the Q. 2931 terminated portion X01 writes a proper value in the routing tag table of the ATM switch in the ATM system to set the connection (step Z02), and notifies the terminal #n (X04n) that the connection is set (step Z03). When the terminal #n (X04n) can receive the newly set connection, after the terminal #n (X04n) performs a process for receiving the connection, the terminal #n (X04n) notifies the Q. 2931 terminated portion X01 that the process for receiving the connection is performed (step Z04). When the Q. 2931 terminated portion X01 receives the connection receivable notification from the terminal #n (X04n), the Q. 2931 terminated portion X01 notifies the terminal #2 (X042) of connection setting completion (step Z05). In this manner, since the connection Y01 is set between the terminal #2 and the terminal #n, the terminal #2 (X042) communicates with the terminal #n (X04n) by using the connection Y01 to transfer the process #2 (X052) from the terminal #2 (X042) to the terminal #n (X04n) (step Z06). At the same time, the terminal #2 (X042) uses a connection X03 to notify the terminal #1 (X041) that the process #2 (X052) executed on the terminal #2 (X042) is migrated to the terminal #n (X04n), i.e., that process migration is performed (step Z07).

When the terminal #1 (X041) is notified of process migration as described above, the terminal #1 (X041) temporarily stops execution of the process #1 (X051) and, at the same time, requests the Q. 2931 terminated portion X01 to set the connection between the terminal #1 (X041) and the terminal #n (X04n) serving as a migration destination (step Z08). When the Q. 2931 terminated portion X01 receives the request to set a connection, the Q. 2931 terminated portion X01 rewrites the routing tag table of the ATM switch on the route of the connection with a proper value to set the requested connection (step Z09). Upon completion of connection setting, the Q. 2931 terminated portion X01 notifies the terminal #n (X04n) that the connection is set (step Z10). When the terminal #n (X04n) is notified of connection setting, after the terminal #n (X04n) performs a predetermined process for receiving the connection, and notifies the Q. 2931 terminated portion X01 that reception of the connection is completed (step Z11).

When the terminal #n (X04n) notifies the Q. 2931 terminated portion X01 of the reception of the connection, the Q. 2931 terminated portion X01 notifies the terminal #1 (X041) which performs the connection setting request that the connection setting is completed (step Z12).

Since the connection Y02 between the terminal #1 (X041) and the terminal #n (X04n) is set by the above procedure, the terminal #1 (X041) uses the connection X03 and the connection Y02 to notify the terminal #2 (X042) and the terminal #n (X04n) that execution of the process #1 (X051) and the process #2 (X052) can be restarted (step Z13). By using this notification as a trigger, execution of the process #1 (X051) on the terminal #1 (X041) and execution of the process #2 (X052) on the terminal #n (X04n) are restarted.

On the ATM communication system, the connection X03 which has not been used in the communication between the process #1 (X051) and the process #2 (X052) and the connection Y01 used in only migration are still set. In order to release these connections, after the execution of the process #1 (X051) and the process #2 (X052) are restarted, the terminal #1 (X041) and the terminal #2 (X042) request the Q. 2931 terminated portion X01 to release the connection X02 and the connection Y01, respectively.

A sequences for releasing the connection X02 are shown in steps Z14, Z15, Z16, Z17, and Z18 in FIG. 33 (45), and a sequence for releasing the connection Y01 are shown in steps Z19, Z20, Z21, Z22, and Z23. Each sequence performs connection release according to the following sequence. The terminal of a connection release request sender sends a connection release request to the Q. 2931 terminated portion X01. When the Q. 2931 terminated portion X01 receives the connection release request, the Q. 2931 terminated portion X01 notifies the other terminal which performs communication by using the connection of connection release. The terminal notified of connection release executes a predetermined process executed in connection release, and then notifies the Q. 2931 terminated portion X01 that the connection release is received. When the connection release is received, the Q. 2931 terminated portion X01 changes the routing tag table of the ATM switch on the route of the connection to be released into a proper value, thereby releasing the connection. Upon completion of this operation, the Q. 2931 terminated portion X01 notifies the terminal which requires the connection release that the connection release is completed.

The above operation is a process which is executed when the process #2 (X052) is migrated from the terminal #2 (X042) to the terminal #n (X04n).

As is apparent from the above description, when process migration is to be executed on the conventional ATM communication system, connection setting/release must be performed many times. In addition, since the connection setting/release is executed by the Q. 2931 terminated portion X01, the throughput of the Q. 2931 terminated portion X01 must be increased to rapidly execute process migration, and a time required for rewriting the routing tag of the ATM switch must be shortened. However, when these measures are executed, the cost of the ATM communication system disadvantageously increases.

In addition, it should be noted that, as the values of the VPI/VCI used for identifying the connection Y02 by the process #1 (X051) and the process #2 (X052), i.e., the values of the VPI/VCI used when these processes send/receive a cell, values set when the connection X03 is used cannot be directly used. In the conventional ATM communication system, the VPI/VCI for identifying a connection on each physical link is managed by the Q. 2931 terminated portion X01, and the Q. 2931 terminated portion X01 notifies the VPI/VCI at the terminal point of the connection Y02 to the terminal #n in connection setting report at reporting connection setup in step Z10 and to the terminal #1 in connection setting completion in step Z12. The terminals #1 (X041) and #n (X04n) must use the notified VPI/VCI to identify message to the processes #1 (X051) and #2 (X052), thereby performing routing to a required process. From the terminal #n viewpoint, this fact means that it must be recognized that the set connection is a new connection set according to process migration in step Z10 in which connection setting is reported. This recognition can be executed by the following manner. That is, information indicating that the connection is a new connection according to process migration is written as user-user information serving as one information element of a Q. 2931 message, and the terminal in which the connection is set refers to the user-user information to perform matching between the notified VPI/VCI and the process using the VPI/VCI.

However, a change in VPI/VCI used before/after migration means that, when migration occurs, not only the migrated process but also a process whose execution is restarted on the same terminal refer to the information element of the message sent from the Q. 2931 terminated portion X01, the connections used when these processes input and output information must be reconnected. More specifically, the processes must refer to the message sent from the Q. 2931 terminated portion X01 to interact with to all the processes related to the process in which migration occurs. For this reason, a time required for migration is increased.

As described above, in the conventional ATM communication system, the CAD dead-lock occurs and a multi-media application cannot be efficiently executed. In addition, when process migration is to be performed, access to the Q. 2931 terminated portion must be performed in a complex pattern to set and release a large number of connections. In order to perform process migration at a high speed, the throughput of the Q. 2931 terminated portion X01 must be increased, and a time required for rewriting the routing tag of the ATM switch must be shortened. For this reason, the cost of the ATM switch disadvantageously increases. In addition, in order to realize high-speed process migration, it is a fault that a large number of processes must be performed to various processes in migration.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an ATM communication system capable of suppressing the occurrence of the CAC dead-lock and rapidly performing process migration without increasing a system cost, a process switching method in the ATM communication system, and a process migration method in the ATM communication system.

According to the present invention, there is provided an ATM communication system comprising a plurality of ATM switches, and a plurality of terminals connected to each other through the plurality of ATM switches, wherein, since the bandwidth of a connection required to be set exceeds the remaining bandwidth of at least one physical link between the ATM switches or between the ATM switches and the terminals, when dead-lock occurs because a process executed by one of the plurality of terminals is blocked, the process executed by the ATM communication system intercepts the bandwidth of at least one physical link obtained by a blocked process group to allocate a bandwidth required by the process which requires the connection setting.

According to the present invention, there is provided an ATM communication system comprising a plurality of ATM switches, a plurality of terminals connected to each other through the ATM switches, a connection setting section for controlling the plurality of ATM switches to set an n:n bi-directional ATM connection having n terminals of the plurality of terminals as n terminal points and using the same VPI and VCI of a cell header serving as a connection identifier for identifying the n terminal points, a process identifier allocating section for allocating, to a plurality of processes for sending a message to the bidirectional ATM connection, a process identifier for identifying the processes, and a migrating section for migrating the process executed on an arbitrary terminal of the n terminals to another terminal of the n terminals while the process identifier allocated to the processes by the process identifier allocating section.

According to the first aspect of the present invention, there is provided a process migration method in an ATM communication system comprising the steps of: setting, through a plurality of ATM switches, an n:n bidirectional ATM connection having n terminals of a plurality of terminals as terminal points and using the same connection identifier for identifying the n terminal points; allocating, to a plurality of processes, executed by the n terminals, for sending a message to the bidirectional ATM connection, the process identifier for identifying the processes; and migrating the process executed on an arbitrary terminal of the n terminals to another terminal of the n terminals while keeping the process identifier allocated to the processes.

According to the second aspect of the present invention, there is provided a handover processing method in an ATM communication system in which a plurality of fixed terminals and a plurality of mobile terminal interface apparatuses arranged on different radio zones for interfacing mobile terminals are connected to each other through a plurality of ATM switches, comprising the steps of: setting an n:m first unidirectional ATM connection having n terminals of the plurality of fixed terminals as input side terminal points and m mobile terminal interface apparatuses of the plurality of mobile terminal interface apparatus and an m:n second unidirectional ATM connection having the m mobile terminal interface apparatus as input side terminal points and the n fixed terminals as output side terminal points by controlling the plurality of ATM switches; allocating the same connection identifier to identify the m input side terminal points of the first unidirectional ATM connection and identify the m output side terminals of the second unidirectional ATM connection; and specifying an ATM connection used in communication with the fixed terminals with the connection identifier allocated by the connection identifier allocating section when the mobile terminal communicates with the fixed terminal while moving.

According to the first aspect of the present invention, when process migration in which a process (process for transferring a message to an ATM connection) executed in a certain terminal is migrated to another terminal is to be performed, since the ATM connection for executing process migration is preset in n terminals including the terminal in which the process migration is executed, unlike the prior art, connection setting/release need not be performed by a Q. 2931 terminated portion. As the ATM connection for executing the process migration, an n:n bi-directional ATM connection having the same identifier at a terminal point is set. A process identifier used to perform a process of transferring a message to the bidirectional ATM connection is allocated to a process subjected to migration, and the process identifier is not changed before/after the migration. For this reason, influence on an inter-process communication process following the migration is minimized. Therefore, process migration can be performed at a speed higher than that in the prior art. In addition, since the process migration is performed without the Q. 2931 terminated portion, the throughput of the Q. 2931 terminated portion need not be increased, and a time required for rewriting the routing take of the ATM exchanger need not be shortened. For this reason, the cost of the ATM communication can be reduced.

The process which performs communication by the n:n bidirectional ATM connection sends/receives, through the ATM connection, a message of a single cell including the process identifier and the identifier of the terminal in which the process is executed, so that process identifiers respectively used by processes are exchanged with each other. In this case, when each process can access the n:n bidirectional ATM connection, the corresponding process can know unused process identifier by receiving only the notified message. For this reason, a new process can be easily added.

In a process of allocating a resource to be managed to a resource managing process group, when a process identifier is used to identify processes from each other, even if process migration in which a terminal in which one arbitrary process of the resource managing process group is merged to another terminal occurs, the process can conceal the occurrence of the process migration from the other resource managing processes. In addition, when resource identifiers of the resource managing process group can be made globally unique, even if a resource managing process is migrated, data of the resource managing process need not be rewritten. For this reason, high-speed process migration can be performed.

According to another aspect of the present invention, the connection identifier of the m output terminal points of an n:m first unidirectional ATM connection is made identical to the connection identifier of the m input terminal points of an n:m second unidirectional ATM connection. For this reason, even if a mobile terminal which accesses these input/output terminal points changes an access point, i.e., moves the access point to a different radio zone, an ATM connection used for communication with a fixed terminal without changing the connection identifier can be set to continue the communication, and migration of the mobile terminal, i.e., a handover process, can be performed with a simple protocol.

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention and, together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.

FIG. 1 is a view showing the arrangement of an ATM communication system according to Embodiment 2 of the present invention;

FIG. 2 is a flow chart showing a schematic procedure for process migration in Embodiment 1;

FIG. 3 is a view for explaining a setting method on the merging side of an n:n bidirectional ATM connection in Embodiment 1;

FIG. 4 is a view for explaining a first setting method on the copy side of the n:n bidirectional ATM connection in Embodiment 1;

FIG. 5 is a view for explaining a second setting method on the copy side of the n:n bidirectional ATM connection in Embodiment 1;

FIG. 6 is a view for explaining a third setting method on the copy side of the n:n bidirectional ATM connection in Embodiment 1;

FIG. 7 is a schematic view showing an n:n bi-directional ATM connection;

FIG. 8 is a schematic view showing the arrangement of an ATM communication system according to Embodiment 2 of the present invention;

FIG. 9 is a schematic view showing an m:n uni-directional ATM connection in Embodiment 2;

FIG. 10 is a view showing the arrangement of a system in which the first application of the present invention according to Embodiment 3 of the present invention;

FIG. 11 is a view showing the physical arrangement of radio zones and radio clusters in Embodiment 3;

FIG. 12 is a view showing an ATM connection set to execute the first application;

FIG. 13 is a flow chart showing a schematic procedure for a handover process in Embodiment 3:

FIG. 14 is a view showing the arrangement of a mobile terminal control section in Embodiment 3;

FIG. 15 is a view showing a method of setting a movement control connection in Embodiment 3:

FIG. 16 is a view showing message sequences exchanged between a mobile terminal and a communication network in Embodiment 3;

FIG. 17 is a view showing the format of an MID operation message in Embodiment 3;

FIG. 18 is a view showing the arrangement of a system in which the second application of the present invention is executed according to Embodiment 4 of the present invention;

FIG. 19 is a view showing the correspondence between physical resources and resource managing processes in Embodiment 4;

FIG. 20 is a view showing the correspondence among a resource managing process, a user process, and a process scheduler in Embodiment 4;

FIG. 21 is a view showing the principle of CAC dead-lock detection in the second application;

FIG. 22 is a view for explaining a process group for explaining the detailed operation of the second application;

FIG. 23 is a view for explaining a resource request of each process of the process group for explaining the detailed operation of the second application;

FIG. 24 is a first view for explaining a process scheduling by the second application;

FIG. 25 is a second view for explaining a process scheduling by the second application;

FIG. 26 is a third view for explaining a process scheduling by the second application;

FIG. 27 is a fourth view for explaining a process scheduling by the second application;

FIG. 28 is a fifth view for explaining a process scheduling by the second application;

FIGS. 29A and 29B are views showing the arrangement of a process queue used when the bandwidth of one physical link is allocated to a plurality of processes in Embodiment 4;

FIG. 30 is a view showing a process arrangement used when the present invention is applied to the second application;

FIG. 31 is a view showing the arrangement of a conventional ATM communication system;

FIG. 32 is a view for explaining process migration in the conventional ATM communication system; and

FIG. 33 is a view showing an executing procedure for process migration in the conventional ATM communication system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below with reference to the accompanying drawings.

The problem of process migration is described first.

FIG. 1 is a view showing the schematic arrangement of an ATM communication system according to an embodiment of the present invention, and shows the following state. That is, four terminals #1 to #4 (1011 to 1014) are connected to each other through three ATM switches #1 to #3 (1021 to 1023), and an n:n bidirectional ATM connection 103 having the terminals #1 to #4 (1011 to 1014) as terminal points is set. As a matter of course, physical links are present between the ATM switches and between the ATM switches and the terminals in which the n:n bidirectional ATM connection 103 is set. However, the physical links are omitted in FIG. 1 for descriptive convenience. In this example, as the n:n bidirectional ATM connection 103, a 4:4 bidirectional ATM connection is constituted by four terminals and three ATM switches. As a matter of course, an ATM communication system constituted by an n:n bidirectional ATM connection can be applied as an ATM communication system constituted by an arbitrary number of terminals and an arbitrary number of ATM switches.

In the terminals #1 to #4 (1011 to 1014), four processes #1 to #4 (1061 to 1064) which perform a process with interaction communicate with each other through the n:n bidirectional ATM connection 103. In this case, when process migration is performed according to the present invention, i.e., when the processes #1 to #4 (1061 to 1064) respectively executed in the terminals #1 to #4 (1011 to 1014) are migrated to other terminals #i (101i), it is one characteristic feature that some or all of the ATM switches #1 to #3 (1021 to 1023) are controlled by a connection setting section 104 to preset the n:n bidirectional ATM connection 103 to the terminals #i in which processes #i may be executed. The present invention also has the following characteristic feature. That is, the n:n bidirectional ATM connection 103 uses the same identifier (VPI/VCI in this example) as the connection identifiers for identifying the connection in the terminals #1 to #4 (1011 to 1014).

Note that the number of the processes are not limited to four, and the number may be larger or smaller than four. In this case, the following description is performed while the number of processes is assumed as four. In addition, communication need not be performed by using the n:n bidirectional ATM connection 103 having the number of branches which is equal to the number of processes, and an n:n bi-directional ATM connection having the number of branches which is larger than the number of processes can be used.

Assume that a variable length message is used to perform communication of the processes #1 to #4 (1061 to 1064). In this case, as well known, an adaptation process must be performed for each process and its bi-directional ATM connection 103. This adaptation process includes a cellulating packetization process for packetizing the length message into a series of fixed length cells, and a message assembling process for assembling the fixed length cells to reproduce a variable length message on the basis of the fixed length cells. In this case, in the terminals #1 to #4 (1011 to 1014), cellulating section 1071 to 1074 and message assembly sections 1081 to 1084 are arranged between the processes #1 to #4 (1061 to 1064) and the bi-directional ATM connection 103. Assume that, in the adaptation process in this case, an AAL3/4 defined by I. 363 of ITU-T standards is applied. The SAR sub-layer of the AAL3/4 includes an identifier called an MID. By using the MID, a plurality of messages simultaneously transferred can be correctly assembled in the same VPI/VCI.

Note that the adaptation process applied to the present invention is not limited to the AAL3/4 described in this embodiment, and any adaptation process in which, even if a plurality of messages are simultaneously transferred to the same VPI/VCI as described above, the messages can be correctly assembled may be used. In this case, information such as the MID of the AAL3/4 indicating that the same identifier is added to the cells formed from the same message, i.e., that the cells are from the same message source is present in the header portion of an adaptation layer.

The connection setting section 104 may be, e.g., a network control function which is set by a maintenance person of an ATM communication system from an OAM interface comprising an ATM switch such as SNMP/CMIS/CMIP, or may be a network control function which is set by a request from a terminal according to a call setting protocol such as Q. 2931 or a call setting program disclosed in Japanese Patent Application No. 6-31180. More specifically, the execution position of the connection setting section 104 may be the ATM switch of terminal in the ATM communication system. In the following concrete embodiments, the execution position of the ATM connection setting by the connection setting section 104 is both the ATM switch and terminal.

When the processes #1 to #4 (1061 to 1064) executed on the terminals #1 to #4 (1011 to 1014) change a message into cells and send the cells to the n:n bidirectional ATM connection 103, the terminals #1 to #4 (1011 to 1014) use process identifiers (to be referred to as process IDs hereinafter) added to the processes #1 to #4 (1061 to 1064) to change the message into cells in the cellulating section 1071 to 1074. In this case, when the processes #1 to #4 (1061 to 1064) executed on the terminals #1 to #4 (1011 to 1014) are migrated to other terminals, the same process IDs can be used before/after the migration to make cells from the message in sending them.

The process IDs are notified to the terminals #1 to #4 (1011 to 1014) by a process ID allocation section 105 when the processes #1 to #4 (1061 to 1064) are started or the n:n bidirectional ATM connection 103 is set. The processes #1 to #4 (1061 to 1064) themselves may have the function of the process ID allocation section 105, or another function of the ATM switch or another process of the terminal may have the function of the process ID allocation section 105. When the processes #1 to #4 (1061 to 1064) themselves have the function of the process ID allocation section 105, a method of statically acquiring process IDs in which the maintenance person of the ATM communication system allocates the process IDs in advance when a program for realizing the processes is described, or a method of causing the processes to communicate with each other to dynamically acquire the process IDs used by the processes may be used. The following concrete embodiments have the following two cases. That is, the process ID allocation section 105 is realized in such a manner that the process ID allocation section 105 is distributed into the processes which perform interaction by using the bidirectional ATM connection 103, and allocation of process IDs is performed in another process on the terminal side or on the ATM switch side.

<Procedure of Process Migration>

A schematic procedure of process migration in this embodiment will be described below with reference to the flow chart shown in FIG. 2.

When a service in which a process migration is predicted is started on an ATM communication system, the connection setting section 104 sets the bi-directional ATM connection 103 having the same connection identifier through the ATM switches #1 to #3 (1021 to 1023) (step S11).

The process ID allocation section 105 allocates the process IDs for identifying these processes to the plurality of processes #1 to #4 (1061 to 1064) which send a message to the bidirectional ATM connection 103 (step S12).

When a process migration request is generated, processes #i (106i) executed in arbitrary terminals #i (101i) of the n terminals #1 to #4 (1011 to 1014) are migrated to other terminals #j (101j) of the n terminals #1 to #4 (1011 to 1014) while process IDs allocated to the processes are held (step S13).

With the above procedure, the process migration in which the processes #i (106i) executed in the terminals #i (101i) are migrated to the terminals #j (101j) is executed.

<Concrete Operation of Embodiment 1>

The operation of this embodiment will be more concretely described below. The processes #1 to #4 (1061 to 1064) executed on the terminals #1 to #4 (1011 to 1014) are connected to each other by the 4:4 bi-directional ATM connection 103. An MID serving as a process identifier used when a message is sent to the bidirectional ATM connection 103 is allocated to each of the processes #i (106i). When each message received from the processes #i (106i) is to be divided into cells by a cellulating sections 107i, the MID is added to each of the divided pieces. When the messages are to be assembled by message assembly sections 108i, cells having the same MID are gathered to assemble the messages. In this manner, even if cells from a plurality of message sources are merged and given to the message assembly sections 108i, the message assembly sections 108i can correctly reproduce the messages unless the arriving order of the cells sent from the same process in each process is the same as the sending order of the cells in the 4:4 bi-directional ATM connection 103.

This MID is allocated to each process in such a manner that the same MID is not used among the processes which perform communication by the same bidirectional ATM connection, i.e., that the same number is prevented from being used. This allocating method will be described later.

When each of the processes #i (106i) tries to transfer some information to another process, the process #i (106i) changes the information into a message and sends the message to a corresponding one of the cellulating sections 107i. Each of the cellulating sections 107i divides the received message into cells and sends the cells to the bidirectional ATM connection 103. The bidirectional ATM connection 103 temporarily merges the cells sent from each of the cellulating sections 107i, copies each cell and sends the copies to each of the message assembly sections 108i. The message assembly section 108i refers to the MIDs of the received cells to gather the cells from the same message source, and assembles a message by referring to information except for the MIDs defined by I. 363 of the ITU-T standards. As a result, a message sent from one process is reproduced in all the message assembly sections 108i. In this case, since a message transferred with the MID used in a corresponding one of the cellulating sections 107i is a message formed and sent by the corresponding process 106i, the message assembly section 108i may discard such a message.

The message assembly sections 108i sequentially send the assembled messages to the processes #i (106i). For this reason, a message sent from one of the processes #i (106i) is received by one of processes #j (106j). Process migration means, for example, that the positions of the process #1 (1061) and the process #2 (1062) in the state shown in FIG. 1 are replaced with each other. At this time, when the processes #1 and #2 migrate together with their MIDs, i.e., when the MID used in the cellulating section 1071 and the MID used in the cellulating section 1072 are changed into 2 and 1, respectively, on the basis of the processes #3 and #4, it cannot be recognized that the processes are migrated. More specifically, migration of the processes does not influence other processes. From this point of view, the MID is can be regarded as a kind of identifier added to a process. The number of processes which can send and receive messages according to the above principle is determined by the bit length of the MID. According to I. 363 of the ITU-T standards, since an ID has 10 bits, a maximum of 1024 processes can perform communication.

As is apparent from the above description, VPI/VCI is not used to execute a message division process or a message assembly process for performing communication between these processes and indicate the destination of a message. For this reason, The VPI/VCI at each of the input/output points between the 4:4 bidirectional ATM connection 103 and the processes may have any value. In consideration of execution of process migration, the VPI/VCI values at the input/output points between the 4:4 bidirectional ATM connection and all the processes are preferably equal to each other such that communication can be performed with the same VPI/VCI in the destination to the process is migrated. That is, a message is changed into cells with the same VPI/VCI value in any input/output point, the cells are sent, and the message is preferably assembled by using the cells received with the same VPI/VCI value.

Assume that an adaptation process, called AAL5, in which, when a plurality of messages are simultaneously transferred with the same VPI/VCI, these messages cannot be correctly assembled, is to be applied. In this case, for example, a process may be identified by using a VCI in place of an MID such that an n:n bi-directional ATM connection is not presented by VC switching but is presented by VP switching. In this case, the same VPI is desirably used at the input/output points between the ATM connection and the processes. According to this method, a maximum of 2.sup.16 (=65536) can be connected to the same n:n connection. However, when the number of processes connected to the same n:n bidirectional ATM connection excessively increases, the following problems are posed. That is, (1) fault location identification, i.e. finding a faulty process, cannot be easily performed when a fault occurs, (2) a VPI/VCI space is pressed, i.e., a maximum of 255 (when a cell format at an interface point is UNI) n:n duplex connections described above are set, and (3) since the MID may be uniquely defined in the n:n bidirectional connection, the MID need not be changed at a position where the n:n bidirectional connection is set, but, since the VPI/VCI is uniquely defined at each interface point, the VPI/VCI may have to be changed in migration. For this reason, one of process identification by the VCI and process identification by the MID is selected depending on an application to be applied. Several services which can be presented will be described below according to the principle of the present invention. In these services, an application in which process identification is performed by using the VCI and application in which process identification is performed by using the MID are performed.

Note that a protocol in which an information element having the same mean as that of the MID is added to each cell may be defined as a user protocol on the AAL5. When the user protocol is defined as described above, a problem that process identification must be performed by the VPI/VCI in the AAL5 can be solved. In addition, in this case, unlike a case wherein an AAL3/4 is used, a user can set an MID having an arbitrary length. For this reason, the number of processes which perform communication on one n:n bi-directional connection and are subjected to migration can be set to be larger than 1024.

A method of realizing an n:n bidirectional connection on the ATM communication system, which plays an important role in this embodiment, will be described below.

<Arranging Method on Merging Side of n:n Duplex Connection>

FIG. 3 shows a method of realizing a portion where cells from message sources sent from the processes in an n:n bidirectional connection are merged. FIG. 3 shows only a portion to which the present invention is applied and which is cut from an ATM communication network. Terminals #1 to #4 (2011 to 2014) are connected to each other by ATM switch #1 to #3 (2021 to 2023) and VC links #1 to #7 (2031 to 2037). The ATM communication network is constituted by not only the terminals, the ATM switches, and the VC links, but also other terminals, ATM switches, and VC links. In addition, the number of terminals, ATM switches, and VC links and the connection state thereof included in the portion to which the present invention is applied are not limited to the number and states shown in FIG. 3, as a matter of course. In addition, the ATM switches and terminals are connected to each other by optical fibers, STP (Shielded Twisted Pair) cables, or UTP (Unshielded Twisted Pair) cables, in a full duplex form, i.e., the ATM switches and terminals are connected such a manner that transmission and reception can be simultaneously performed. In order to avoid cumbersome illustration, the above state is not shown in FIG. 3. Assume that the physical links are arranged at positions where at least the VC links #i (203i) are set.

The processes #i which communicate using an n:n bidirectional connection are substantiated by the calculation capability of terminals #j to be executed. More specifically, the terminals to which the present invention is applied can be regarded as a kind of "field". The processes are mapped on terminals selected according to a predetermined procedure to be executed. As a matter of course, the terminals #j in which the processes #i are executed are not necessarily fixed. In particular, when process migration is executed, a process #b executed on a terminal #a is temporarily stopped and, the process #b and its execution environment are migrated to a terminal #c. In addition, the processes #i need not be present at all the terminal points (positions where the processes #i transmit and receive messages) of a set n:n bidirectional connection. The n:n bidirectional connection may be set such that terminals are prepared for all the terminals which can be regarded as migration destinations.

Referring to FIG. 3, in order to structure the "field", constituted by the terminals #1 to #4 (2011 to 2014), for executing processes, only the VC links #1 to #7 (2031 to 2037) for merging messages in the VC links set in the ATM communication network are shown. A VC connection for merging messages is arranged in such a manner that the VC links #1 to #7 (2031 to 2037) are connected to each other by the ATM switch #1 to #3 (2021 to 2023). In this case, each VC link means a route for a cell which is transferred on one physical link by the same VPI and the same VCI. In addition, chaining of VC links means that a cell transferred on one VC link is sent to another VC link on a predetermined desired physical link, and is executed by an ATM switch #i (202i).

The chaining of VC links executed by the ATM switch #i (202i) is not limited to chaining shown in FIG. 3, and the moment the chaining of VC links is performed, chaining of VC links according to distribution of merging traffic (to be described later) is performed. In addition, if an ordinary point-to-point ATM connection is set between the terminal #1 (2011) and the terminal #2 (2012), the ATM switch #2 (2022) executes chaining of VC links for constituting the ATM connection simultaneously with the above chaining of the VC links executed by the ATM switch #i (202i).

In each of the ATM switches #i (202i), when cells are input from the VC links #i (203i) allocated to the merging side of an n:n bidirectional connection, the cells are transferred to a predetermined one of VC links #j (203j). For example, in the ATM switch #2 (2022), cells input from the VC link #1 (2031) and the VC link #2 (2032) are transferred to the VC link #5 (2035). More specifically, the VPI fields and VCI fields of all the cells input from the VC link #1 (2031) and the VC link #2 (2032) are rewritten into the VPI/VCI allocated to the VC link #5 (2035), and the cells are sent to the physical link set in the VC link #5 (2035).

For this reason, each of the ATM switches #i (202i) has a header conversion function for rewriting the header portion of a cell input from each physical link and a function of transferring the input cell to a desired physical link. As the ATM switch capable realizing these functions, an ATM switch disclosed in U.S. Pat. No. 5,274,641 can be used. However, since the method of realizing this ATM switch does not influence the validity of the present invention, the description of the present invention is carried out without being limited to the disclosed ATM switch.

As shown in FIG. 3, VC links are chained in a tree structure by the ATM switches #i (202i) to constitute the merging side of the n:n bidirectional ATM connection. Due to the VC connection having the tree structure, cells sent from the terminals #i (201i) serving as the "field" for process execution are finally transferred to the root of the tree structure to be merged to the VC link #7 (2037). In this case, in chaining of VC links in each ATM switch, it is required in the ITU-T standards that cells from given VC links are input to other VC links while keeping the sending order of the cells on the given VC links, i.e., that the cell order is kept. For this reason, in a merging traffic which is finally formed, it should be noted that a cell flow from the same terminal keeps an order in sending. For this reason, when a cell flow formed by copying the above cell flow to an ATM layer is send to each terminal, a message included in the cell flow can be correctly assembled in each terminal.

Note that an order of cells among terminals is not assured in the merging traffic. More specifically, with respect to cells simultaneously sent from the terminals #1 and #2, depending on the operation timing of an asynchronous portion of the operation of the ATM switch #2, the cell may be sent from the terminal #1 first or the cell may be sent from the terminal #2 first.

When the cells sent from respective terminals are merged with each other, traffic sent from a plurality of terminals are gathered in VC links near the root of the tree structure. As a result, a bandwidth which must be allocated to the VC links increases in width. In order to prevent another communication from being adversely affected, a plurality of ATM switches must execute a function which is known as UPC (Usage Parameter Control) and is to control a bandwidth used in each VC link.

The UPC in each ATM switch may be executed in the following manner in the example shown in FIG. 3:

policing performed by input portion:bandwidth T1 of the ATM switch #2 of the VC link #1,

policing performed by input portion:bandwidth T2 of the ATM switch #2 of the VC link #2,

policing performed by input portion:bandwidth T3 of the ATM switch #3 of the VC link #3, and

policing performed by input portion:bandwidth T4 of the ATM switch #3 of the VC link #4.

As described above, it is the first method of the UPC that a bandwidth used when each terminal sends a cell to the 4:4 bidirectional ATM connection 103 is restricted in advance. According to this method, a point at which the UPC is performed is limited to the input portion of the ATM switch including the terminal, and other VC links need not execute the UPC. For this reason, it is satisfactory that the other VC links only execute CAC (connection acceptance control) based on the sum of bandwidths which are allowed to be used by terminals giving traffics.

The CAC, as well known, controls that the sum of bandwidths given to VC links set on physical links does not exceed the data transmission capability of the physical links. Although the CAC can be executed by only bandwidth management performed by a connection setting function, the UPC generally requires special hardware for executing the UPC. For this reason, this method can advantageously reduce the hardware required for the UPC, but each terminal cannot send a cell to a bandwidth T5 (T5=T1+T2+T3+T4 in the example described above) allowed to be used by a VC link (VC link #7 in FIG. 3) of the root portion of the merging traffic. Therefore, the peak flow rate of a cell which can be sent from each terminal is disadvantageously limited to a specific value.

The second method of the UPC executed on each ATM switch is as follows. That is, at the input portion of the ATM switch of VC links constituting the merging side of the n:n bidirectional ATM connection, policing is performed by the bandwidth T5 allowed to be used by the root of the merging side. In this case, each terminal can use up to the bandwidth T5 as a peak bandwidth. On the other hand, when a peak is allocated to each terminal, and when a plurality of terminals simultaneously give cell flows in peak bandwidths, adverse influence such as degradation of cell discarding rate is given to other connections treated by the ATM switches #i. In order to prevent this, the UPC must be performed at the input portion of the ATM switch of VC links constituting the merging side of the n:n bidirectional ATM connection, or at the output portion of the ATM switch of VC links constituting the merging side of the n:n bidirectional ATM connection. According to this method, a peak bandwidth in which each terminal can send a cell can be advantageously made large. On the other hand, UPC must be executed on a transmission path between an ATM switch and an ATM switch, and an amount of hardware for executing the UPC increases. Therefore, the second method has characteristics opposing the characteristics of the first embodiment.

In each of the first and second embodiments, as the method of the UPC, not only policing (when a bandwidth exceeds a limited band, cells are discarded until the bandwidth is equal to the limited bandwidth), but also shaping (when a bandwidth exceeds a limited band, sending of cells is stopped until the bandwidth is equal to the limited bandwidth) can be used. When shaping is performed, unlike a case wherein policing is performed, discarding of cells is not caused even if burst signals sent from the terminals collide with each other on an ATM switch. However, since a cell buffer must be arranged to temporarily wait sending of cells, an amount of hardware required for shaping disadvantageously increases.

Note that various methods of arranging the policing and shaping are known, and an example of the methods is disclosed in U.S. Pat. No. 5,274,641. Since this arranging method does not influence the validity of the present invention, the description of the present invention is carried out without being limited to the arranging method.

As described above, cell flows merged on the merging side of the n:n bidirectional ATM connection are transferred to the terminals while being copied. This portion is called a copy side of the n:n bi-directional ATM connection.

<Arranging Method on Copy Side of n:n Duplex ATM Connection>

FIG. 4 shows the first arranging method on the copy side of the n:n bidirectional ATM connection. FIG. 4 shows the arrangement of the copy side of the n:n bidirectional ATM connection when a "field", for process execution, constituted by the terminals #1 to #4 (2011 to 2014) shown in FIG. 3. The terminals and ATM switches in FIG. 4 are the same as those in FIG. 3, and the same reference numerals as in FIG. 3 denote the same parts in FIG. 4. VC links in FIG. 4 are different from the VC links shown in FIG. 3, and reference numerals different those in FIG. 3 are added to the VC links in FIG. 4. In addition, as in FIG. 3, physical links in which the VC links are set are not omitted in FIG. 4 to avoid cumbersome illustration.

The arranging method shown in FIG. 4 is an arranging method which can be applied when each of the ATM switches #i (202i) has a known function as a copy function. It is known that an ATM switch with copy function has various arrangements. The present inventor discloses one of the arrangements of ATM switches in Japanese Patent Application No. 6-140223. Since this arranging method does not influence the validity of the present invention, the description of the present invention is carried out without being limited to the arranging method.

As in the merging side of the n:n bidirectional ATM connection, VC links #8 to #14 (3011 to 3017) are chained in a tree structure by the ATM switches #i (202i). In each ATM switch, a predetermined number of copies are formed with respect to cells input from VC links constituting the copy side of the n:n bi-directional ATM connection, and the input cells and the copies of the cells are sent to predetermined VC links such that the cells and copies can be transferred to the terminals #i (201i) along the tree structure. For example, in the ATM switch #2 (2022), one copy of a cell input from the VC link #9 (3012) is formed, the input cell and the copy are sent to the VC link #11 (3014) and the VC link #12 (3015), respectively. As a result, respective cells constituting cell flows merged on the merging side of the n:n bidirectional ATM connection are transferred to the terminals #i (201i) realizing the "field" for execution of only one process. Therefore, the merging side shown in FIG. 3 is connected to the copy side shown in FIG. 4. More specifically, when the VC link #7 (2037) and the VC link #8 (3011) are connected to each other by an arbitrary ATM switch, a desired n:n bidirectional ATM connection can be realized.

In this case, it should be noted that UPC need not be executed in the VC links constituting the copy side of the n:n bidirectional ATM connection. It is satisfactory that only CAC is performed in a bandwidth allocated to the merging traffic at each physical link.

FIG. 5 shows the second arranging method on the copy side of the n:n bidirectional ATM connection. FIG. 5 shows the arrangement of the copy side of n:n bidirectional ATM connection when the "field", for process execution, constituted by the terminals #1 to #4 (2011 to 2014) shown in FIG. 3. The terminals and ATM switches in FIG. 5 are the same as those in FIG. 3, and the same reference numerals as in FIG. 3 denote the same parts in FIG. 5. VC links in FIG. 5 are different from the VC links shown in FIG. 3 or 4, and reference numerals different those in FIG. 3 or 4 are added to the VC links in FIG. 5. In addition, as in FIG. 3, physical links in which the VC links are set are not omitted in FIG. 5 to avoid cumbersome illustration.

The arranging method on the copy side shown in FIG. 5 is a method which can be applied when each of the ATM switches #i (202i) does not have a copy function. Since each of the ATM switches #i (202i) does not have a copy function, each of the terminals #i (201i) realizes a function which can be substituted for the copy function.

Traffics merged on the merging side are input to a VC link #15 (4011) at any place in the ATM communication network, and are input to the ATM switch #1 (2021). In the ATM switch #1 (2021), the traffics are output to a VC link #16 (4012). Subsequently, in the ATM switch #2 (2023), the traffics are related from the VC link #16 (4012) to a VC link #17 (4013). As a result, the merging traffic is given to the terminal #4 (2014) first. The terminal #4 (2014) receives the merging traffic and rearranges a message, and, at the same time, loops the merging traffic to input it to a VC link #18 (4014). Similarly, the merging traffic is caused to sequentially pass through VC links #19 to #24 (4015 to 4020), thereby giving the merging traffic to the terminal #3 (2013), the terminal #2 (2012), the terminal #1 (2011).

In the arranging method shown in FIG. 5, since each of the ATM switches #i (202i) has no copy function, the terminal #i (201i) loops the merging traffic to obtain the substitution of the copy function. For this reason, the arranging method shown in FIG. 5 has the following disadvantages compared with the arranging method shown in FIG. 4. (1) The route of the n:n bidirectional ATM connection is larger, and latency is degraded. (2) Since the calculation capability required to the terminals #i (201i) increases, a bandwidth which can be given to the merging traffic (since looping is performed at the terminals #i (201i), the physical link identical to that of the merging side of the n:n bidirectional ATM connection is used) is smaller than that of the arrangement in FIG. 4. (3) Although the n:n bidirectional ATM connection does not operate when a fault occurs at the terminals #i (201i). However, this arranging method has the advantage that a function such as a copy function which increases a hardware scale is not required, and the VC links #i (202i) can be advantageously constituted at low cost.

In each VC link in the arrangement shown in FIG. 5, as in the arrangement shown in FIG. 4, it is satisfactory that only CAC is performed without performing UPC.

As a matter of course, the copy side of the n:n bidirectional ATM connection cannot be formed by methods other than the methods shown in FIGS. 4 and 5. The copy side of the n:n bidirectional ATM connection can be formed by the following manner obtained by combining the formats shown in FIGS. 4 and 5. That is, in particular, when each ATM switch has a copy function with a small bandwidth, for example, when each ATM switch includes a cell switch realizing only a point-point connection, and a copy function for forming a desired number of copies of a cell input from the cell switch to be returned to the cell switch is connected to one inlet/outlet pair of the cell switch, as shown in FIG. 6, the merged traffic is copied into several branches by one of the copy function, and one of the branches is sent to one of the terminals performing loopbacking the marged traffic in order to hand another terminal sequentially, and another branch is sent to another copy function in order to make copy traffics which are sent some terminals directly.

In the setting format of the n:n bidirectional ATM connection described above, whether a communication resource can be effectively used is largely dependent on the function of ATM switches constituting the ATM communication network and its physical topology. However, from the point of view for performing the present invention, the n:n bidirectional ATM connection may be set in any format. Therefore, in this case, assume that the setting format of the copy side of the n:n bidirectional ATM connection is determined by a policy decided by the manager of the ATM communication network, and the description of the present invention is carried out without being limited to the setting format.

The above is the description of a method of constituting the n:n bidirectional ATM connection. Note that, in order to cumbersome illustration, the n:n bidirectional ATM connection is schematically shown in FIG. 7. In order to clearly show that the ATM connection is a bidirectional connection, two arrows having different directions are drawn at each input portion of the connection 103.

(Embodiment 2)

The present invention can be applied in not only a situation wherein messages sent from all processes must be received as shown in FIG. 1, but also a situation a process group for sending messages is different from a process group for receiving the messages. FIG. 8 shows a situation wherein four processes for sending messages and two processes for receiving the messages are present. Such a situation occurs in a case wherein respective processes specially realize different functions, e.g., so-called server client computing. Other concrete examples wherein such a situation occurs will be described later.

In the embodiment shown in FIG. 8, four processes (to be referred to as sending processes hereinafter) #1 to #4 (7011 to 7014) for sending messages are connected to the information input side of a 4:2 uni-directional ATM connection 702, and two processes (to be referred to as reception processes hereinafter) #1 (7031) and #2 (7032) are connected to the information output side of the 4:2 unidirectional ATM connection 702. As in the embodiment in FIG. 1, the number of processes is not limited to a value in the embodiment shown in FIG. 8. This embodiment can be applied when a smaller number of processes or a larger number of processes are used. In addition, the embodiment is not applied only when the number of sending processes is larger than the number of reception processes, but can be applied when the number of reception processes is larger than the number of sending processes. In this case, four sending processes and two reception processes are set as one example, and the following description is carried out. Communication need not be performed by an m:n ATM unidirectional connection having branches equal to processes in number, an m:n ATM unidirectional having branches larger than processes in number can be used as in FIG. 1.

In addition, VPI/VCI values sent from the sending processes to the 4:2 unidirectional ATM connection 702 are equal to each other in the sending processes, and VPI/VCI values received by the reception processes from 4:2 unidirectional ATM connection 702 are equal to each other in the reception processes. These conditions are desirable to execute process migration as in FIG. 1. It is to be determined by the nature of an application whether the VPI/VCI values used by the sending processes are equal to each other or not or whether the VPI/VCI values used by the reception processes are equal to each other or not.

<Actual Operation of Second Embodiment>

Messages sent from sending processes #i (701i) to the 4:2 unidirectional ATM connection 702 are given to the processes #1 (7031) and #2 (7032) through the 4:2 unidirectional ATM connection 702. As in the case shown in FIG. 1, in order to perform communication and to use a variable length message, cellulating functions 1035 to 1038 in an adaptation process are arranged between the sending processes and the 4:2 unidirectional ATM connection 702, and message assembly functions 1045 and 1046 of the adaptation process are arranged between the 4:2 unidirectional ATM connection 702 and the reception processes. Functions realized by these cellulating functions and message assembly functions are the same as those in FIG. 1. Therefore, when the MIDs of an AAL3/4 are allocated to the sending processes #i (701i) for sending messages to the 4:2 unidirectional ATM connection 702, according to the following manner, messages sent from the sending processes #i (701i) can be received by reception processes #i (703i).

The messages sent from the sending processes #i (701i) are changed into cells by cellulating functions (103i), and the cells are given to the 4:2 uni-directional ATM connection 702. After the 4:2 uni-directional ATM connection 702 merges the given cells, the 4:2 unidirectional ATM connection 702 gives the merged cells to message assembly functions 104i. The message assembly functions 104i reproduces messages with reference to the MIDs belonging to the sending processes, and gives the messages to the corresponding reception processes #i (703i), respectively. A method of allocating the MIDs to the sending processes #i (701i) will be described below. Note that when an adaptation protocol such as an AAL5 which does not include an MID is used, as in the case shown in FIG. 1, it is considered that an m:n unidirectional ATM connection is presented by a VP switch, a VCI may be used in place of the MID, or the MID may be defined on the AAL5 as a user protocol as described above.

Therefore, even if migration of a sending process in the sending processes or migration of a reception process in the reception processes occurs, the occurrence of the process migration can be concealed from a process in which migration does not occur, and high-speed process migration can be realized at low cost.

<Method of Setting m:n Unilateral ATM Connection>

A method of setting an m:n unidirectional ATM connection in an ATM communication network can be easily estimated based on the setting method on the merging side of the n:n bidirectional ATM connection shown in FIG. 2 and the setting method on the copy side of the n:n bidirectional ATM connection shown in FIGS. 4 to 6. For example, when a "field" where the sending processes #i (701i) are executed and a "field" where reception processes #j (703j) are executed are different terminals, the following operation is preferably performed. That is, the input terminal of the merging side is connected to the terminal which is the "field" where the reception processes #i (703i) are executed, and the output terminal of the copy side is connected to the terminal which is the "field" where the reception processes #j (703j) are executed. When a VC link where a merging traffic is constituted on the merging side is connected to the root of the copy side, an m:n unidirectional ATM connection capable of performing a desired operation can be obtained.

As in the case wherein UPC is performed in the n:n bidirectional ATM connection, UPC in the m:n uni-directional ATM connection is preferably performed by policing or shaping performed by bandwidths allocated to the terminals at the output portions of the terminals which are "fields" of sending process execution or policing or shaping performed by bandwidth allocated to merging traffics in the physical links where the connection on the merging side is set.

In order to avoid cumbersome illustration, the m:n unidirectional ATM connection is schematically shown in FIG. 9. In order to clearly show that the ATM connection is a unidirectional connection, arrows having directions toward the connection 702 are drawn at the input portions of the connection 702, and arrows having direction toward the output portions of the connection 702 are drawn at the output portions of the connection 702.

The above description about the basic embodiments of the present invention is completed. Services which can be presented to a user of a communication network will be described below by performing the present invention. By this description, the spirit of the present invention will be clearly shown.

A compromise mobile terminal service on a CATV network which is the first application to which the present invention is applied will be described below in detail.

The mobile terminal service, as represented by a mobile telephone or a portable telephone, is a service in which a subscriber can perform communication while moving. In order to make it possible that a subscriber (mobile terminal) can perform communication while moving, a process which is generally called a handover process and in which a radio zone used in communication between the mobile terminal and a fixed terminal is switched according to moving of the mobile terminal. In this case, when the subscriber or the mobile terminal is regarded as a process in which communication is performed while the subscriber moves, this handover process can be equivalently regarded as a kind of process migration. According to the present invention, as described later, the handover process can be simply realized.

FIG. 10 shows the arrangement of a CATV network in which the first application of the present invention is executed. In the CATV network, ATM switches #1 (E011) and #2 (E012) are connected to each other, and a plurality of radio zone forming sections #1-1 to #1-m (E0311 to E031m) and radio zone forming sections #2-1 to #2-m (E0321 to E032n) which are mobile terminal interface units are interfaced by passive star optical couplers #1 (E021) and #2 (E022). The passive star optical coupler is an optical part for coupling a plurality of optical fibers so that the light signal input from one of the optical fibers is uniformly distributed and output to the remaining optical fibers.

In the CATV network having the arrangement shown in FIG. 10, a backbone network is constituted by ATM switches (E01i). The CATV network has an object to interface subscribers at low cost by the passive star optical couplers (E02i) on which information transmission is performed in an ATM manner. In a range shown in FIG. 10, the radio zone forming sections only are connected to the passive star optical coupler. However, an user's local machine called a set top box and a radio zone forming section may be connected together to a single passive star optical coupler. In this manner, it is a great advantage of the ATM CATV network that a single passive star optical coupler can be used for various purposes.

Each of the radio zone forming sections #1-j (E03ij) respectively constitute radio zones. When a mobile terminal (E041) using the second application is in any one of the radio zones, the mobile terminal (E041) can perform speech communication or data communication with a communication destination GOC through a mobile terminal controller E051 which can be regarded as a fixed terminal. In this case, a radio channel in the radio zone may be an ATM radio channel disclosed by the present inventor in Japanese Patent Application No. 5-349634. The following description is carried out with assuming that communication is performed by this radio channel. When an ATM radio channel is used, a mobile terminal can relatively freely use not only a bandwidth of 64 kbps but also various bandwidths of, e.g., 8 kbps or 128 kbps. As a result, as a service presented to the mobile terminal (E041), not only a speech communication service but also a data transfer service which requires a relatively small number of bits and in which a subscriber holding the mobile terminal (E041) notifies another subscriber of a place where the subscriber holding the mobile terminal (E041) can be presented at low cost.

In addition, when a mobile terminal in communication is stopped in one radio zone, and does not move to another radio zone (i.e., no handover process is performed), a data transfer service, such as downloading of a file of a computer, having a high bit rate can also presented. In this case, it should be noted that the handover process must be stopped only while wide-band communication is performed. For example, the following service can be easily realized. That is, while a user of a mobile terminal performs communication in walking, the user stops when the mobile terminal accesses a relatively large file, the user begins to walk when the access to the file is completed.

The radio zone forming sections #1-j (E03ij) broadcast cell flows (cell flows of downstream links) given from the ATM switches (E01i) through the passive star optical couplers E02i to the radio zones formed by the radio zone forming sections #1-j (E03ij), and, at the same time, gives cells (cell flows of upper stream links) sent from a mobile terminal being present in the radio zone formed the radio zone forming sections #1-j (E03ij) to the ATM switches through the passive star optical couplers E02i. As disclosed by the present inventor in Japanese Patent Application No. 5-349634, a carrier frequency for carrying the cell flows of the downstream links is made different from the carrier frequency for carrying the cell flows of the upper stream links to make full duplex communication possible. The radio zone forming sections #i-j may have various arrangements. For example, each radio zone forming section may have the arrangement disclosed in Japanese Patent Application No. 5-349634. However, the radio zone forming section described in Japanese Patent Application No. 5-349634 is designed to be directly connected to an ATM switch, but exchanges cells with an ATM switch through a passive star optical coupler. When a radio zone forming section exchanges cells with an ATM switch through a passive star optical coupler, a function for measuring the distance between the radio zone forming section and the ATM switch, a function of changing a timing for sending a cell flow, and a access protocol for sharing the upper stream link with other radio zone forming sections must be executed. It is assumed that the radio zone forming section described in this case includes these functions. Since a method of the access protocol in the upper stream link of the passive star optical coupler does not influence the validity, the description of the present invention is carried out without being limited to this method. For example, the scheme disclosed by the present inventor in Japanese Patent Application No. 6-140223 may be used.

When the mobile terminal E041 tries to start communication, and the mobile terminal E041 is present at a radio zone, the mobile terminal E041 outputs a connection setting request to a network side by using the control information channel of the radio zone. In response to the connection setting request, a required connection is set inside of the communication network. The mobile terminal E041 performs communication by using the connection set up as described above. Upon completion of the communication, the mobile terminal E041 outputs a connection release request to the network side. In response to the connection release request, the connection which has been used by the mobile terminal E041 is released. A communication method in the control information channel of the radio zone will be described later.

A handover process is controlled by the mobile terminal controller (E051) connected to the ATM switch #1 (E011). This mobile terminal controller (E051), in the handover process, has (a) a connection function for controlling the ATM switches #1 (E011) and #2 (E012) to set an n:m unidirectional ATM connection (e.g., G03) having the mobile terminal controller (E051) as an input side terminal point and m radio zone forming sections of the radio zone forming sections #1-j (E03il) serving as the mobile terminal interface units as output side terminal points, and an m:n uni-directional ATM connection (e.g., G04) having m radio zone forming sections of the radio zone forming sections #1-j (E03il) as input side terminal points, and the mobile terminal controller (E051) which is n fixed terminal as an output terminal point, and (2) a connection identifier allocating function for allocating the same connection identifier for identification of the m input side terminals of the n:m unidirectional ATM connection and identification of the m output side terminals of the m:n uni-directional ATM connection. In the example shown in FIG. 12, only the mobile terminal controller (E051) is used, and n=1. However, when n=2 or more, the present invention can be applied. When viewing from these ATM connections, the mobile terminal controller can be regarded as a kind of a fixed terminal.

When an ATM switch receives a connection setting request from a mobile terminal, the ATM switch sets an ATM connection (to be described later) between the mobile terminal controller E051 and each of the radio zone forming sections E03ij. Although a connection must be reformed during communication by a mobile terminal, this sends a connection reform request toward an ATM switch.

<Method of Realizing Handover Process>

A method of realizing a handover process by the mobile terminal controller E051, the ATM switches E01i, and the radio zone forming sections E03ij in the second application of the present invention will be described below.

Before interaction among the mobile terminal controller E051, the ATM switches E01i, and the radio zone forming sections E03ij is actually described, a method of setting a radio zone for realizing the handover process will be described below.

As shown in FIG. 11, a CATV network company installs the radio zones along roads in a city area where the company performs services in such a manner the radio zones partially overlap on each other. At this time, the frequencies of radio waves used in the overlapping portions of the radio zones are set to be different from each other. Note that radio zones (called radio clusters) formed by the radio zone forming sections connected to one passive star optical coupler are continuously arranged along the roads as shown in FIG. 11. The diameter of each of these radio zones is set to be small, e.g., 100 m, to obtain high-speed data transmission at low cost in the radio zone.

On the other hand, the mobile terminal always monitors frequencies used as downstream links in the CATV network, and operates to reproduce information by using, of these frequencies, a reception radio wave of a reception having the highest reception intensity. A radio wave which transfer information of a downstream link is monitored to automatically select a radio zone. In addition, a handover process can be realized at low cost by setting a connection in the following manner.

In this case, the pairs of frequencies of the downstream links and the upper stream links are not changed. More specifically, is should be noted that the following relationship is fixed in the CATV network. That is an upper stream link in the radio zone in which a downstream link has a frequency of fd1 is fu1, and a down stream link in the radio zone in which a downstream link has a frequency of fd2 is fu2. Therefore, when the frequency of the downstream link used by the mobile terminal is determined, the frequency of the upper stream link can be automatically determined, and information can be sent to the radio zone.

These radio zones are not necessarily arranged along the roads in the city area. For example, a radio zone is preferably installed at a dangerous place (e.g., pond) in the city area. A parent gives his/her child a radio terminal, and an alarm is given to the parent when the child gets close to a dangerous place while the child has fun in the city area. In addition, a radio zone may be installed the rooms such as a living room and dining room of the house of each subscriber. It is assumed that a CATV network manager installs a radio zone at a position where a subscriber wants to use the above service.

Sincerely, FIG. 12 shows connections set between the mobile terminal controller E051 and each of the radio zone forming sections E03ij when a mobile terminal service is executed. These connections are set inside the ATM communication network in calling from the mobile terminal or call arriving to the mobile terminal. Although data transfer routes are also required in calling from each mobile terminal or call arriving from each mobile terminal, the data transfer routes will be described later. In order to avoid cumbersome illustration, these routes are omitted in FIG. 12. In addition, when a mobile terminal performs calling, or call arriving to mobile terminal is received, a specific radio zone in which the mobile terminal is located must be notified to the network side. This will be described below.

In calling from the mobile terminal E041 or call arriving to the mobile terminal E041, 1:m uni-directional ATM connections G03 and G0A and m:1 uni-directional ATM connections G04 and G09 are set on each of the passive star optical couplers E02i, and these connections are connected to the mobile terminal controller E041 by 1:1 unidirectional ATM connections G01, G02, G05, G06, G07, and G08.

A 1:1 bidirectional ATM connection G0B is set between a communication destination G0C of the mobile terminal and the mobile terminal controller E051. In this case, it is assumed that the communication destination G0C of the mobile terminal does not move and is seamlessly connected to the mobile terminal controller E051 by an ordinary ATM connection. When the communication destination G0C of the mobile terminal is a mobile terminal, as in the case shown in FIG. 12, a 1:m unidirectional ATM connection and an m:1 unidirectional ATM connection are set toward the mobile terminal serving as the communication destination, and these connections are connected to the mobile terminal controller E041 by the 1:1 uni-directional ATM connection.

The 1:m unidirectional ATM connection G03 and the m:1 unidirectional ATM connection G04 is used to realize a handover process with respect to moving the mobile terminal E041 between the radio zones formed by the radio zone forming sections E031j connected to the same passive star optical coupler, i.e., in a radio cluster.

The 1:m unidirectional ATM connections G04 and G0A are spontaneously set when ATM connections are set in the passive star optical coupler by the nature of the passive star optical coupler. In the radio zones formed by the radio zone forming sections E031j connected to the same passive star optical coupler, cells which treats the same information can be received by the same VPI/VCI. Therefore, as described above, the mobile terminal E041 operates to reproduce information on the basis of a reception radio wave having the highest response intensity, and the radio zones are arranged to geographically overlap. For this reason, even if the mobile terminal moves between the radio zones, in the same radio cluster, frame synchronization and cell synchronization are released when the reception frequency is changed by moving the radio zones. Only when an operation for reestablish the frame synchronization and cell synchronization, mobile terminal E041 can continue communication. That is, an interrupt time of the reception information is short even if the radio zones are changed.

At this time, it should be noted that the VPI/VCI of extracted cells need not be changed. When information such as voice information whose interrupt can be interpolated is used, the interrupt time of the reception information can be shorter than a time which can be interpolated or neglected by human being, communication can be continued without interrupting a connection. In an ATM radio channel disclosed in Japanese Patent Application No. 5-349634, the interrupt time of radio information in the radio channel is a time required to establish frame synchronization and cell synchronization. When a frame structure is properly selected by shortening the overhead interval of the frames of the radio channel, the interrupt time of the reception information can be suppressed with in a required range. In this case, when communication in which the frame synchronization and cell synchronization between the radio zones are not allowed to be reestablished is to be performed, it is apparent that communication is preferably performed when a user does not move between the radio zones, i.e., when a user stops. Since ATM radio zones are used, when a service in which a user performs speech communication with walking, receives a transferred file with stopping, and performs speech communication again with walking is performed, it should be noted that a simple method in which a new ATM connection having a bandwidth required to perform file transfer is set is performed.

When a mobile terminal sends information in the radio cluster, a cell is preferably sent by a simply allocated VPI/VCI. The sent cell is naturally transferred to a portion of a desired communication destination through the 1:1 unidirectional ATM connection G02 by the operation of the m:1 uni-directional ATM connection G04.

By realizing only the above processes, a switching process of the radio zones performed when a handover process in the radio cluster, i.e., when a mobile terminal moves from a radio zone to another radio zone in the same radio cluster. In this case, when the handover process is performed in only a single radio cluster, the mobile terminal controller E051 is not required. The 1:1 unidirectional ATM connections G01 and G02 are preferably connected to the 1:1 bi-directional ATM connection G0B for the communication destination G0C.

However, in order to realize relatively high speed communication at low cost, the diameter of a radio zone formed by radio zone forming sections E03ij is desirably small, i.e., 100 m. For this reason, a radio cluster constituted by one passive star optical coupler can not present compromise mobile terminal service to the entire area required by subscribers of the CATV network. Therefore, a handover process between a plurality of radio clusters must be performed. The mobile terminal controller E051 is arranged to perform the handover process between the plurality of radio clusters.

When calling to a radio terminal or call arriving to the radio terminal occurs, the network sets the connection shown in FIG. 12 in a given radio cluster in which the radio terminal is present, and, at the same time, the same connection as described above is set in a radio cluster adjacent to the given radio cluster. In FIG. 12, the connections G03 and G04 correspond to the given radio cluster in which the radio terminal is currently present. On the other hand, the ATM connections G09 and G0A correspond to the radio cluster adjacent to the given radio cluster.

The mobile terminal controller E051 chains the connection on the radio cluster in which the mobile terminal is present to the connection to the communication destination, and, at the same time, chains the connection set on the radio cluster adjacent to the radio cluster to the connection to the communication destination. More specifically, in the example shown in FIG. 12, cell flows given from the connection G0B to the mobile terminal controller E051 are copied, and the obtained copies are given to the connections G01 and G05. At the same time, the cell flows given from the connection G02 and G06 are merged and given to the connection G0B. In this manner, a cell flow sent from the communication destination G0C is given to the radio cluster in which the mobile terminal E041 is present and a cluster adjacent to the radio cluster. For this reason, even if the mobile terminal E041 is given to the radio cluster, when the mobile terminal reproduces information on the basis of a radio wave having the highest intensity, the reception information can be switched by the same process as that in which reception information is switched while the radio terminal moves between the radio zones in the same radio cluster. In addition, when the mobile terminal E041 is currently present in a given radio cluster or a radio cluster adjacent to the given cluster, a cell sent from the mobile terminal E041 is given to the communication destination. As a result, a handover process between the radio clusters can be performed by the same process as the handover process between the radio zones in the radio cluster.

Note that when the handover process between the radio clusters occurs, the adjacent radio cluster is changed. More specifically, a radio cluster which is not the adjacent cluster becomes the adjacent radio cluster, or a radio cluster which is regarded as the adjacent radio cluster becomes a radio cluster which is not adjacent.

In the radio cluster which is newly used as the adjacent cluster, the connection shown in FIG. 12 is set for a new handover process. In each radio zone in the new adjacent radio cluster, the same VPI/VCI as that used in another radio cluster is used as matter of course. This connection setting is requested by the mobile terminal controller E051 to the communication network. In order to realize this, the position of the mobile terminal must be notified to the mobile terminal controller E051. For this purpose, a 1:1 bi-directional connection is set between the mobile terminal controller E051 and each of the radio zone forming sections E03ij, and each radio zone forming section may notify the mobile terminal controller E051 of the position of the radio terminal, or the following method may be used. That is, as will be described later, each radio zone forming section broadcasts an identifier allocated to the radio zone forming section to a radio zone formed by the radio zone forming section, an identifier allocated to the radio zone is received by the mobile terminal E041, and the identifier is notified to the mobile terminal controller E051.

Connections set on a radio cluster which has been an adjacent radio cluster are preferably released for effective used of a communication bandwidth. On the other hand, since a probability that the mobile terminal E041 returns to the same radio cluster is high, in order to reduce a process amount related to a handover process, it is preferred that the connections remain to be released. It is determined by the behavior pattern of a human being having the mobile terminal E041 whether these connections are released or reduced. However, if the connections are released, the mobile terminal controller E051 requests the network to release the connections.

As described above, since connection setting/release according to a handover process can be performed after the mobile terminal moves between radio clusters, the above described method can advantageously perform a high-speed handover process with a low-cost structure.

When the CATV network according to the present invention is used, the mobile terminal service must perform a process which is different from communication performed by an ordinary ATM connection and is related to the special connection described above. For this reason, the mobile terminal service is regarded as an optional service, i.e., a service which need not be performed. In this case, as in a conventional ATM communication system as shown in FIG. 12, a connection setting section G0D may be arranged, and the mobile terminal controller E051 may request the connection setting section G0D to perform connection setting according to the mobile terminal.

The connection setting section G0D receives a request from the mobile terminal controller E051 or a request of another ordinary ATM connection setting and controls the ATM switches E011 and E012 in the ATM communication system, thereby setting the ATM connection. From this point of view, the mobile terminal controller E051 is added to the ATM communication system, and functions as a fixed terminal for realizing a kind of service function for realizing a special service (mobile terminal, in this case). As described above, since the special service is realized as the fixed terminal, a packaging method which is advantage in cost and in which the special service can be realized with a desired ATM communication network by only connecting the fixed terminal to the ATM switch can be obtained.

<Schematic Procedure of Handover Process>

The schematic procedure of the handover process described above will be described below with reference to FIG. 13. When a mobile terminal moves between radio clusters, for a handover process between the radio clusters, the mobile terminal controller E051 requests an n:m unidirectional ATM connection and an m:n unidirectional ATM connection to be set (step S21). At this time, the connection setting section (G0D) of the ATM communication network sets requested connections while allocating the same connection identifiers (VPI/VCI in this example) to identify m input side terminal points of the requested n:m unidirectional ATM connection and identify m output terminal side end terminals of the m:n unidirectional ATM connection (step S22). In this manner, preparation for the handover process of the mobile terminal E041 between the radio clusters is completed. Even if the mobile terminal E041 is subjected to a handover process between the radio clusters, an ATM connection used in communication with the mobile terminal controller E051 can be specified by the VPI/VCI above described, thereby realizing the handover process (step S23).

FIG. 14 shows the arrangement of the mobile terminal controller E051 for realizing the handover process described above. The mobile terminal controller E051 is constituted by a physical layer section H01, a pay load cipher section H02, a pay load decoding section H03, a subscriber cipher key table H04, a control cell branch/insert section H05, a VPI/VCI rewriting section H06, a copy tag adding section H08, a copy buffer H07, and a control processor H09.

The mobile terminal controller E051 has a function of chaining connections set to radio clusters to a connection set to the communication destination of a mobile terminal, a function of realizing a handover process between the radio clusters, and a cipher function of the pay load portion of a cell to improve security which is always problem in a mobile terminal service. These functions are sequentially described below.

The function of chaining the connections set to the radio clusters to the connection set to the communication destination of the mobile terminal is described first. This function is constituted by a function of copying a cell given from the communication destination of the mobile terminal to send the copy to the radio cluster in which the mobile terminal is present and to an adjacent radio cluster, and a function of transferring the cell given from the mobile terminal to the communication destination.

In this embodiment, since the mobile terminal controller E051 is connected to the ATM switch #1 (E011) by a physical link, an ATM connection set to execute the mobile terminal service must be designed to identify the mobile terminal controller E051. More specifically, the interface points between the mobile terminal controller E051 and the ATM switch #1 (E011), different VPI/VCIs are added. The mobile terminal controller E051 can identify a radio cluster to which a cell is sent when the cell is sent to a specific VPI/VCI. In addition, in order to cause the mobile terminal controller E051 to present a mobile terminal service to a plurality of mobile terminals at once, the mobile terminal controller E051 must be able to identify ATM connections requested to mobile terminals. More specifically, the mobile terminal controller E051 can identify a mobile terminal to which a cell is sent when the cell is sent to a specific VPI/VCI. For this reason, an identifier for identifying a mobile terminal serving as a process migrated in the first application is not the MID serving as a process identifier used in the ATM-SYSTEM shown in FIG. 1 but the VPI/VCI serving as a connection identifier.

In order to chain connections set to the radio clusters to a connection set to the communication destination, the following process is preferably performed.

A function of copying a cell received from the communication destination of the mobile terminal to send the copy to a radio cluster in which the mobile terminal is present and the adjacent radio cluster is described first. As will be described below, this function is realized by a cell copy function of forming a plurality of cell flows.

Cell flows given from the communication destination G0C through the connection G0B are given to the reception side of the physical layer section H01 through an ATM switch. The physical layer section H01 performs a frame synchronization process and a cell synchronization process to a bit stream given from the ATM switch to reproduce cell flows. The cell flows are given to the copy tag adding section H08 through the pay load decoding section H03 and the control cell branch/insert section H05. The copy tag adding section H08 refers to the VPI/VCIs of the given cell flows to add information called a copy tag to the cells, and gives the cells to the copy buffer H07. In each copy tag, information indicating a connection to which the cell belongs and the number of copies to be formed. The former is called a copy connection identification, and the later is called the number of copies. For example, in the connection arrangement shown in FIG. 12, cells input from the connection G0B is transferred to the connection G01 and the connection G05, and the number of copies is set to be 2. The copy connection identification is uniquely added to each connection processed by the mobile terminal controller E051 to identify communication between the mobile terminal E041 and the communication destination G0C. For example, in order to identify this connection, value 1 is set as the value of the copy connection identification.

The copy buffer H07 refers to the number of input cells, forms copies which is equal in number to the number of copies, gives the copies to the VPI/VCI rewriting section H06. In this case, the copy buffer H07 writes sequence numbers in a field in which the number of copies is written in the sending order of the copies of the same cell. This sequence numbers are called copy numbers. For example, a cell input when the number of copies=4 is output from the copy buffer H07 four times. At this time, the copy numbers of the output copied cells are changed one, two, three four. This copy number are used to select a connection to which the copied cells are sent in the VPI/VCI rewriting section H06. Note that a field for copy connection identification is transparently output in the copy buffer H07.

The cells output from the copy buffer H07 are input to the VPI/VCI rewriting section H06. The VPI/VCI rewriting section H06 refers to the connection identification and the copy numbers to identify a connection to which the cells are to be sent. The VPI/VCI rewriting section H06 rewrites the VPI/VCI fields of the cells with VPI/VCI values for identify the connection, deletes the copy tags, and gives the cells to the transmission side of the physical layer section H01 through the control cell branch/insert section H05 and the pay load cipher section H02. When a plurality of cells from the same cell source having VPI/VCIs which can be respectively transferred to desired clusters are sent to the ATM switch, routing of these cells in the ATM switch can be performed, and these cells are transferred to the desired clusters as a matter of course. For example, in the connection arrangement shown in FIG. 12, since the copy connection identification is 1, it can be recognized that the cells are to be transferred to the connection G01 or G05. For example, if a cell having copy number 1 and a cell having copy number 2 are to be sent to the connections G01 and G05, respectively, the VPI/VCI of the cell having the copy connection identification of 1 and copy number 1 is rewritten with a value for identifying the connection G01, and the VPI/VCI of the cell having the copy connection identification of 1 and copy number 2 is rewritten with a value for identifying the connection G05.

Note that a VPI/VCI added to other terminal points of these connections, i.e., the same VPI/VCI allocated to each mobile terminal and used in all the radio zones to simplify the handover process and the VPI/VCI of a cell sent from the VPI/VCI rewriting section H06 have different values, respectively. The VPI/VCIs at terminal points on the radio zone sides of these connections are sent from an ATM switch to a passive star optical coupler or rewritten by a radio zone forming section.

With the above operation, cells sent from the communication destination G0C are transferred to desired radio clusters, and the cells having desired VPI/VCIs are given to the mobile terminal E041.

The cells sent from mobile terminals, as described above, are given to the mobile terminal controller E051 through the m:1 unidirectional ATM connection. At this time, it is noticed that a connection is set such a manner that a cell sent from a specific mobile terminal can be identified by the VPI/VCIs of the cells sent from the mobile terminals in the input portion of the mobile terminal controller E051. In this case, the mobile terminal controller E051 treats the input cells as described above, the cells can be transferred from the connections set in the radio clusters to a connection set to the communication destination of the mobile terminal.

A cell input from the connection G01 or G06, like the cell input from the connection G0B, is input to the copy tag adding section H08 through the physical layer section H01, the pay load decoding section H03, and the control cell branch/insert section H05. The copy tag adding section refers to the VPI/VCI allocated to the connection G02 or G06, adds a copy tag to the cell, and transfers the cell to the copy buffer H07. In this case, the number of copies in the copy tag may be 1. As a copy connection identification, the same value is allocated to the connections G02 and G06. Since the number of copies of the cell belonging to the connection G02 or G06 is set to be 1, the copy buffer H07 gives only one of the cells each having copy number 1 to the VPI/VCI rewriting section H06.

When the VPI/VCI rewriting section H06 refers to the copy identification and the copy number and recognizes that the input cell is a cell belonging to the connection G02 or G06, the VPI/VCI rewriting section H06 rewrites the VPI/VCI of the cell with the VPI/VCI allocated to the connection G0B, and outputs the cell to the ATM switch through the control cell branch/insert section H05, the pay load cipher section H02, and the physical layer section H01. When the value of the VPI/VCI is equal to that allocated to the connection G0B, the ATM communication network transfers the cell to the communication destination G0C. As described above, even if the mobile terminal E041 is present in any cluster, the cell sent from the mobile terminal is transferred to a desired communication destination.

When the two operations described above, i.e., an operation of transferring a cell from a communication destination to desired radio clusters and an operation of transferring the cell in the desired radio clusters to a desired communication destination, are performed, chaining between connections set to the radio clusters and a connection set to the communication destination of the mobile terminal can be realized.

The function of realizing an handover process between radio clusters performed in the mobile terminal controller E051 will be described below in detail.

As described above, connections are set in a radio cluster in which a mobile terminal is present and in a radio terminal adjacent to the radio terminal for a handover process. When the request of the handover process is generated, i.e., when the radio cluster in which the mobile terminal changes, a connection is set in a radio cluster adjacent to the new radio cluster for a new handover process. In order to realize the simple handover process described above, a radio cluster in which the mobile terminal must be recognized, and the communication network is requested to set a connection. In order to achieve these objects, the function of the handover process performed by the mobile terminal controller E051 is used. The capability of calculation for the handover process is presented by the control cell branch/insert section H05 and the VPI/VCI rewriting section H06.

FIG. 15 shows a connection set between the radio zone forming sections #1-j (E03ij) and the mobile terminal controller E051 in advance to perform mobile terminal control such as a handover process. A connection of such type is called a movement control connection. FIG. 15 shows only a movement control connection related to the radio zone forming section #i-j belonging to one radio cluster.

A 1:m unidirectional ATM connection I01 and a m:1 unidirectional ATM connection I02 are arranged as movement control connections between the mobile terminal controller E051 and the radio zone forming sections #1-j (E03ij) in each radio cluster. When information is transferred from the radio zone forming sections #1-j (E03ij) to the mobile terminal controller E051, the m:1 unidirectional ATM connection I02 is used; and when information is transferred from the mobile terminal controller E051 to the radio zone forming sections #1-j (E03ij), the 1:m uni-directional ATM connection I01.

A VPI/VCI is added to each cluster between the mobile terminal controller E051 and an ATM switch to identify a movement control connection related to a specific radio cluster. The same VPI/VCI is given to the 1:m unidirectional ATM connection I01 and the m:1 unidirectional ATM connection I02 which constitute the mobile control connection related to one radio cluster. More specifically, when a cell is to be transferred to the radio cluster of the sender of the input cell, a cell having the same value as that of the VPI/VCI of the input cell is given to the movement control connection.

In communication between the radio zone forming sections #1-j (E03ij) and the mobile terminal controller E051, an AAL3 is used as an adaptation layer to obtain a variable length message. For this purpose, an MID is allocated to each of the radio zone forming sections E03ij.

Each radio zone forming section divides a messages into cells by using the allocated MID when the message is to be transferred to the radio zone forming sections E03ij. Thereafter, the VPI/VCI values of these cells are sent as VPI/VCI values allocated to the connection I02 between the radio zone forming sections and a passive star optical coupler. As a result, with the operation of the connection I02, these cells are guided to the mobile terminal controller E051. In the mobile terminal controller E051, a message is assembled by cell flows transferred from the radio clusters with reference to the MIDs. In this manner, the radio cluster which sends a message assembled with reference to the VPI/VCI and the radio cluster which sends a message assembled with reference to the MID are identified by the radio zone forming section.

On the other hand, when the mobile terminal controller E051 sends a message of one of the radio zone forming sections E03ij, the mobile terminal controller E051 divides the message into cells by an MID allocated to the radio zone forming section E03ij to which the cells are to be sent. Thereafter, the VPI/VCI values of the cells are sent as VPI/VCIs allocated to the connection I01 between the mobile terminal controller E051 and the ATM switch. As a result, with the operation of the connection I01, these cells are guided to the radio zone forming sections E03ij in the same radio cluster. The radio zone forming section E03ij extracts only cells each having the same MID as that allocated to the radio zone forming section E03ij to assemble a message.

In the embodiment shown in FIG. 1, a message is changed into cells by an MID allocated to a sender. However, even if the mobile terminal controller E051 changes the message into cells by the MID allocated to a destination, a process for sanding the message to the connection I01 is only the mobile terminal controller. For this reason, it should be noted that normal message assembly can be performed by the radio zone forming sections E03ij without simultaneously changing different messages into cells by the same MID. When packaging is performed as described above, it can be advantageously determined with reference to only an MID whether a message is a message sent to the radio zone forming section, and an unnecessary message does not have to be assembled.

In the mobile terminal controller E051, a cell belonging to the connection I02 is transferred to the control cell branch/insert section H05 through the physical layer section H01 and the pay load decoding section H03. In the control cell branch/insert section H05, a cell given from a radio cluster as information for controlling a mobile terminal is branched to the control processor H09. The branching conditions in the control cell branch/insert section H05 are as follows. That is, the control cell branch/insert section H05 refers to the VPI/VCI of the cell input from the pay load cipher section H02 side, and branches cells having VPI/VCIs allocated to movement control connections set between the mobile terminal controller E051 and the ATM switch to the control processor H09.

A cell belonging to the 1:m unidirectional ATM connection I01 is transferred in the mobile terminal controller E051 in the following manner. The control processor