Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Reexamination Certificate
2001-01-12
2004-08-03
Cangialosi, Salvatore (Department: 2661)
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
C370S902000
Reexamination Certificate
active
06771600
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a packet switch system, applied to a broadband switch, a cross-connect switch, a router etc, for forwarding (that includes switching, transmitting and transferring, unless specifically limited) a packet for managing a communication system together with a user packet.
The present invention relates more particularly to a packet insertion interval control system and a packet insertion interval control method for controlling an insertion interval of management-oriented packets required to be periodically forwarded in order to manage an operation and maintenance of the communication system, and of packets previously accumulated.
An ATM (Asynchronous Transfer Mode) communication system, which is applied to a broadband switch and serves as a packet switch system for forwarding a fixed-length packet (cells), is required to, when transferring cell data of a user cell and an OAM (Operation And Maintenance) cell that are defined as basic data in ATM communications, keep a desired communication quality by controlling a transfer sequence of the cell data.
It is recommended that the OAM cells such as an AIS (Alarm Indication Signal) cell, an RDI (Remote Defect Indication) cell and a CC (Continuity Check) cell be transferred at a given cycle (a cycle of 1 sec according to ITU-T I.610) in order to notify of fault information when a fault occurs and to monitor a normality of connections (a VPC connection and a VC connection multiplexed with the physical layer connection) at all times.
In the ATM communication system for processing a plurality of connections by multiplexing these connections, when generating the cells of each connection at the cycle of 1 sec, if the cells are consecutively inserted into all the connections accommodated therein, a traffic falls into a burst, and consequently the cells are discarded due to an overflow of the cells from a cell buffer (memory) in a cell multiplexer provided at a rear stage. There exists a method of troubleshooting this problem by increasing a buffer capacity, however, this method brings about a scale-up of the hardware. While on the other hand, if the buffer capacity is not increased, a probability of occurrence of discarding the cells increases, resulting in a decline of the communication quality.
Accordingly, the conventional ATM communication system is specially provided with an insertion interval management counter of alarm cells such as the AIS cells, whereby an insertion interval of the alarm cells generated per connection is kept over a predetermined interval, and the alarm cells are controlled so that the alarm cells inserted are not sent in burst (refer to, e.g., Japanese Patent Application Laying-Open Publication Hei 9-107362).
Herein, this type of ATM communication system in the prior art will be explained referring to FIG.
1
. In this ATM communication system, valid data [1] or invalid data [0] of connections ID#
0
, ID#
1
, ID#
2
, . . . ID#n defined as logic paths of the cells, are set beforehand in a connection management table
10
. It is assumed that the connection numbers (ID#
0
, . . . ID#n) and address show one-to-one in the connection management table
10
. A table access management unit
11
, with a trigger that a notification of expiration of a counter value is inputted from an insertion interval management counter
12
at a timing corresponding to a desired cell insertion interval (e.g., a 2-cell interval), indicates an address counter
13
periodically cycling to count up the counter value, and reads the counted-up value as a connection number.
Note that the logic path implies a category of a unit for management when distinguishing between the packets according to a plurality of classes within the packet switch system, and corresponds to a category of connection in the case of a connection-oriented system such as the ATM communication system and, in the case of a connectionless system such as the router system, to a category of a flow, link or session.
Next, the table access management unit
1
, with the value read from the address counter
13
serving as an address, reads the valid/invalid state data from the connection management table
10
, and, if the connection concerned is in a valid state, requests a cell inserting unit
14
to insert the cell (alarm cell).
Thus, when controlling the cell insertion interval, the cell inserting unit
14
forwards the insertion cells at intervals of 2 cells to a cell highway
15
, corresponding to the valid connections. The address counter
13
is so constructed as to make one cycle at an interval of 1 sec, and hence an interval at which the cell is inserted into the same valid connection is 1 sec. This time interval of the cell insertion is based on the above ITU-T Recommendations.
As a result, the insertion interval of the cells generated per connection is kept over a predetermined interval. Note that if the cell insertion interval is not controlled, the insertion cells are forwarded in burst to the cell highway
15
, corresponding to the valid connections.
Further, there exist other types of ATM communication systems each adopting a method of inserting the cell at a given rate by a cell shaping (band regulation) scheme. In this ATM communication system is provided with an insertion interval monitoring counter per connection, and the cell is inserted into the connection of which the insertion interval monitoring counter comes to its expiration.
FIG. 2
shows one example of an architecture of the conventional ATM communication system as a whole. This ATM communication system is constructed of a plurality of input line interfaces
20
, a switch unit
21
, a plurality of output line interfaces
22
and a system management unit
23
. An alarm cell of the fixed-length packet, which is inserted from the cell inserting unit
24
of the input line interface
20
, is switched to a preset route by the switch unit
21
, and forwarded to an output-side cell highway
27
via the output line interface
22
.
Further, the cell inserting unit
24
of each input line interface
20
or a cell inserting unit
25
of each output line interface
22
inserts a new cell, or temporarily stores (buffering) the cells arrived from the cell highway
26
or
27
and inserts the cell at a desired timing. On this occasion, the system management unit
23
sets a serial number of the connection into which the cell should be inserted and insertion timing data for each cell inserting unit
24
or
25
.
Each of the cell inserting units
24
,
25
includes a connection management table
10
, a table access management unit
11
, an insertion interval management counter
12
, an address counter
13
and a cell inserting unit
14
, which constitutes the ATM communication system shown in FIG.
1
.
In this ATM communication system, when inserting the cells, the cell insertion interval and the timing are controlled so that the insertions are not consecutive, i.e., not burst. With this contrivance, it is possible to reduce a buffer capacity of a rear-stage buffer (e.g., when the cell inserting unit
24
of the input line interface
20
inserts the cell, it is a buffer
28
of the switch unit
21
, and, when inserting the cell from the output line interface
25
, it is a switch unit of a next-stage node (unillustrated)).
Based on the system architecture in the prior art, however, the insertion interval management counter for managing the cell insertion interval and the address counter for managing the connections, are individually provided, and therefore, if the number of connections and the insertion interval change per communication system, there is a necessity of previously providing counters corresponding to the number of connections and to the maximum insertion interval as well. This conduces to a problem in which the hardware is scaled up.
Further, there are in fact a less number of connections in use than the number of connections accommodated in the communication system. A problem inherent in the conventio
Kawarai Kenichi
Ohno Yasutaka
Ooba Yasuhiro
Terada Takeshi
Cangialosi Salvatore
Fujitsu Limited
Katten Muchin Zavis & Rosenman
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