Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-11-24
2003-04-22
Kizou, Hassan (Department: 2662)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S310000, C370S321000, C370S395100, C370S396000, C370S400000, C370S410000
Reexamination Certificate
active
06553014
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the 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 in an ATM (Asynchronous Transfer Mode) and a process migration method in the ATM communication system.
2. Description of the Related Art
An ATM (Asynchronous Transfer Mode) attracts attention as a technique aiming at increasing the speed of transmission/switching technique. The ATM is a technique in which all pieces of information are carried by fixed-length short packets called cells to be transferred to aim at packaging hardware for packet exchange, thereby make it easy to transmit/switch information at a high speed.
The ATM is regarded as “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 are 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 are developed.
In the ATM communication system using the ATM technique, before communication, a so-called connection is set between terminals to communicate with each other. When the terminals to communicate with each other sends a cell to the communication system, 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 to transfer 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 constituting 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
(P
021
to P
025
) are connected to each other by hubs #
1
to #
5
(P
011
to P
015
). Physical link pairs P
031
to P
039
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
(P
021
) has a file #
1
(P
041
), the terminal #
2
(P
022
) has a file #
2
(P
042
), and, similarly, the terminal #
5
(P
025
) has a file #
5
(P
045
).
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 does 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, in consideration of execution of applications using communication bandwidths and a resource 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
(P
021
) assures the file #
1
(P
041
) and transfers it to the terminal #
3
(P
023
). In addition, a process B executed on the terminal #
2
(P
022
) 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
(P
041
) first. On the other hand, the process B obtain all the communication bandwidths on physical links P
036
and P
037
. In this state, the process A tries to obtain a route to the file #
3
(P
043
) and the communication bandwidths on the physical links P
036
, P
033
, P
034
, and P
038
. However, at this time, since all the communication bandwidths of the physical link P
036
has been assured by the process B. The process A fails to obtain the communication bandwidths. The process B tries to open the file #
1
(P
041
). However, since the file #
1
(P
041
) has been opened by the process A, the process B fails to open the file. When the processes A and B are slept in this state, a dead-lock state occurs.
Dead-lock of such a type occurs due to conflict of the usage requests of the processes A and B between the file #
1
(P
041
) and the communication bandwidth on the physical link P
036
. More specifically, the dead-lock of such a type occurs such that the CAC is executed to exclusively give the communication bandwidths 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 conflict on the communication bandwidths on the physical link P
036
, 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
(X
041
), #
2
(X
042
), . . . , #n (X
04
n) which are connected to each other by the ATM communication system. In the conventional ATM communication system, a Q. 2931 terminated portion X
01
which terminates Q. 2931 protocol for setting connections is present, a signaling VC#i (X
02
i) is set between the Q. 2931 terminated portion X
01
and the terminals X
04
i. The signaling VC#i (X
02
i) is used to cause each terminal to specify the terminal of a callee or destination for the Q. 2931 terminated portion X
01
. The Q. 2931 terminated portion X
01
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 constitutin
Kabushiki Kaisha Toshiba
Kizou Hassan
Logsdon Joe
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