Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
1999-11-19
2004-09-14
Patel, Ajit (Department: 2664)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S395200
Reexamination Certificate
active
06791946
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to connection control of virtual channels in an ATM (Asynchronous Transfer Mode) communication network, and particularly to a method of connection reservation control of an ATM communication network and an ATM exchange for performing the connection reservation control, wherein virtual channels are left reserved without executing their release.
In an ATM communication network, it is better for the resource efficiency to release a virtual connection every time when a communication, which has been performed thereby, is finished. However, somewhat complicated procedures are required for establishing and releasing the virtual connection.
FIG. 10
is a sequence chart illustrating procedures to be performed for establishing and releasing a virtual connection between a transmitter terminal TE
1
and a receiver terminal TE
2
through a transmitter-side exchange
500
, an intermediate exchange
501
and a receiver-side exchange
502
.
For establishing a virtual connection, the transmitter terminal TE
1
transmits a call setup request SETUP to the transmitter-side exchange
500
. The transmitter-side exchange
500
outputs an address message IAM (Initial Address Message) to the intermediate exchange
501
, which also outputs the same address message IAM to the receiver-side exchange
502
. The receiver-side exchange
502
transmits a call setup request SETUP to the receiver terminal TE
2
. By performing such a sequence of procedures as above described, a virtual connection is established.
In a similar way, a disconnection notification DISC or releasing request REL should be exchanged between the transmitter terminal TE
1
, the transmitter-side exchange
500
, the intermediate exchange
501
, the receiver-side exchange
502
and the receiver terminal TE
2
, for releasing the virtual connection.
FIG. 11
is a block diagram illustrating a configuration example of an ATM exchange taking charge of performing above procedures for establishing or releasing the virtual connection, which is described in a Japanese patent application laid open as a Provisional Publication No. 160851/'93.
Referring to
FIG. 11
, a first signal processing unit
94
performs necessary procedures for connecting a virtual channel between a terminal
100
and the ATM exchange
20
. A second signal processing unit
95
performs necessary procedures for connecting or disconnecting a virtual channel between the ATM exchange
20
and a neighboring node of an ATM network
400
.
Receiving a call setup request from the terminal
100
through a terminal interface
81
and the first signal processing unit
94
, a call processing unit
96
selects a virtual channel of a quality of service demanded by the terminal
100
and transmits an initial address message towards the ATM network
400
through the second signal processing unit
95
.
According to the virtual channel selected by the call processing unit
96
, a channel switch control unit
92
controls a channel switch
85
to switch ATM cells from the terminal
100
according to the selected channel.
In the example of
FIG. 11
, a cross connect processing unit
97
takes charge of selecting an appropriate detour path for each group of virtual channels when a virtual path assigned to the group is congested. According to the selection of the cross connect processing unit
97
, a path switch control unit
93
controls a path switch
86
to switch the virtual channel towards an appropriate port, by way of which ATM cells from the terminal
100
are transmitted through a network interface
82
.
Thus, a virtual channel is connected to the terminal
100
in the ATM exchange
20
.
When a releasing request of the virtual connection is received by the call processing unit
96
from the terminal
100
, the call processing unit
96
retrieves the concerning virtual channel and transfers the releasing request towards the ATM network
400
through the second signal processing unit
95
. The channel switch control unit
92
releases connection of the virtual channel in the ATM exchange
20
by deleting data of the virtual channel from the switching table of the channel switch
85
.
Such procedures as performed in the ATM exchange
20
should be executed in each of: the transmitter-side exchange
500
, intermediate exchange
501
and the receiver-side exchange
502
of
FIG. 10
, for establishing a virtual connection between the transmitter terminal TE
1
and the receiver terminal TE
2
. In other words, the establishment or release of a virtual connection is performed through connecting or disconnecting two neighboring ATM exchanges or an ATM exchange with a terminal with a virtual channel, one by one, by exchanging connection requests or releasing requests between them.
Conventionally, the virtual connection is established or released as above described every time a call setup or a call disconnection is requested from a terminal. However, there have been following problems in such connection control.
First, even for a short suspension of a communication, the virtual connection established for the communication should be released, by disconnecting the concerning virtual channels in every ATM exchange which participates in the virtual connection through exchanging releasing requests between neighboring nodes. And, secondly, even when the virtual connection, which is once released, is to be established again between the same pair of terminals, the same procedures as performed for firstly establishing the virtual connection should be repeated for connecting a virtual channel in every ATM exchange by exchanging connection requests among them.
Therefore, when the call setup request or the call disconnection request occurs frequently, the procedures for connecting or disconnecting virtual channels in the ATM exchanges increase, resulting in degradation of connection establishment ability of the ATM communication network. When the call setup requests and the call disconnection requests of the same pairs of terminals are repeated frequently, the concerning ATM exchanges are forced to repeat duplicated procedures.
A method of resolving this problem is to establish PVCs (Permanent Virtual Connections) between pairs of terminals. However, the PVC is not flexible and therefore uneconomical to be assigned for connecting terminals whereof communication may be interrupted for a long time.
As a prior art for dealing with this problem, a terminal adapter is disclosed in a Japanese patent application laid open as a Provisional Publication No. 239950/'92. In this prior art, when the terminal adapter, which is connecting a terminal A to a communication network for communicating with a terminal B through the network, for example, receives a connection release request of the communication channel from the terminal A, the terminal adapter returns a connection release acknowledge signal to the terminal A. However, the terminal adapter reserves the communication channel being connected for a fixed period without releasing the connection.
Therefore, when a call setup with the terminal B is requested again by the terminal A during the fixed period, the communication between the terminal A and the terminal B can be reopened at once without any procedure for re-establishing the communication channel in the network.
In the prior art, the terminal adapter has two ports and can connect the terminal A also to another terminal C through the network during the fixed period where the communication channel with the terminal B is reserved being connected.
This prior art is somewhat effective for reducing load of exchanges in the communication network for establishing and releasing the virtual connection, in the case where the terminal A repeats communication with the terminal B directly, or alternately with the terminal B and the terminal C, for example, within an interval shorter than the fixed period.
However, in the prior art, the connection reservation control is performed by the terminal adapter. Therefore, there have been following problems.
The first probl
NEC Corporation
Patel Ajit
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