Multi-cast ABR service system and method

Details Multi-cast ABR service system and method Multi-cast ABR service system and method

1998-08-25

2001-06-26

Cangialosi, Salvatore (Department: 2732)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S232000

Reexamination Certificate

active

06252875

ABSTRACT:

BACKGROUNDS OF THE INVENTION
1. Field Of The Invention
The present invention relates to a multi-cast ABR service system and method for performing multi-cast ABR (Available Bit Rate) services in an ATM (Asynchronous Transfer Mode) network or other network.
2. Description Of The Related Art
This kind of multi-cast ABR service is used so that a plurality of receiving terminals could receive identical information at once after being broadcast from a sending terminal in an ATM or other network.
In the ABR (Available Bit Rate) service in the ATM network, a sending terminal recognizes the cell rate of the user cell capable of being transferred in a given time cycle and sends the cell to a receiving terminal by use of a cell called an RM (Resource Management), cell which is different from the user cell between the sending terminal and the receiving terminal. Thus, it is a service for making good use of the band area of a network while restraining the wasting rate of cell.
More specifically, a sending terminal periodically sends a Forward RM cell (hereinafter, abbreviated as an FRM cell) and a receiving terminal having received the FRM cell returns a Backward RM cell (hereinafter, abbreviated as a BRM cell). The rate capable of being transferred, which is called an ER (Explicit Rate), is set up in the RM cell (including the FRM cell and the BRM cell). The ER is rewritten in a receiving terminal and a switch, depending on the congestion in a network. In performing the multi-cast service by the ABR service using this rate control, it is necessary to put together the BRM cells sent from the respective receiving terminals into one RM cell in a switch which would be a branch point.
There are four conventional methods for putting together the BRM cells. Each method will be described hereinafter.
FIG. 4
is a block diagram showing the structure of a multi-cast ABR service system for realizing one of the above mentioned conventional methods. With reference to
FIG. 4
, a sending terminal
10
sends a Forward RM cell with some information and the transferable ER mounted thereon, to a switch
400
. The switch
400
confirms the destination of the FRM cell according to the VPI and VCI included in the FRM cell sent from the sending terminal
10
and classifies each FRM cell. In the switch
400
, ER rewriting units
410
and
430
respectively make a comparison between the ER within the RM cell and the ER set up beforehand and held by the ER rewriting units
410
and
430
and rewrite the ER within the RM cell to take the smaller ER. The switch
400
is provided with buffers
420
and
440
for use in sending the received RM cells. Upon receipt of an FRM cell through the switch
400
, a given receiving terminal of the receiving terminals
41
,
42
, and
43
sends a Backward RM cell toward the sending terminal
10
having sent the FRM cell.
The operation of the multi-cast ABR service system shown in
FIG. 4
will be described, this time.
FIG. 5
is a flow chart for use in describing the operation of the system shown in FIG.
4
. With reference to
FIG. 5
, the sending terminal
10
sends an FRM cell with the sending rate information [ER
0
] mounted thereon, to the receiving terminals
41
to
43
(Step
501
). The FRM cell sent from the sending terminal
10
is broadcast through the switch
400
to all the receiving terminals
41
to
43
(Step
502
). Thus, all the receiving terminals
41
,
42
, and
43
respectively receive the FRM cell (Step
503
).
All the receiving terminals
41
,
42
, and
43
, respectively having received the FRM cell, would try to return each BRM cell to the sending terminal
10
. However, it is only the receiving terminal
41
that can return a BRM cell. This is because only a path from the receiving terminal
41
is extended to the sending terminal
10
and no path from the other receiving terminals
42
and
43
is extended to the sending terminal
10
, in the structure of FIG.
4
.
The receiving terminal
41
sends a BRM cell with the transferable ER [ER
1
] mounted thereon, to the sending terminal
10
(Step
504
). The sending terminal
10
receives the BRM cell (Step
505
) and the ER [ER
1
] within the BRM cell is used so as to perform a rate control of a network for making good use of a band area.
FIG. 6
is a block diagram showing the structure of a multi-cast ABR service system for realizing the other one of the conventional methods. With reference to
FIG. 6
, the sending terminal
10
sends an FRM cell with some information and the transferable ER mounted thereon to a switch
600
. The switch
600
confirms the destination of the FRM cell according to the VPI and VCI included in the FRM cell having sent from the sending terminal
10
and classifies each FRM cell. The ER rewriting units
610
and
630
respectively make a comparison between the ER within the RM cell and the ER set up beforehand and held by the ER rewriting units
610
and
630
and rewrite the ER within the RM cell to take the smaller ER. The switch
600
is provided with buffers
620
and
640
for use in sending the received RM cells.
Upon receipt of the FRM cell through the switch
600
, each of the receiving terminals
41
,
42
, and
43
sends a BRM cell toward the sending terminal
10
having sent the FRM cell. An ER comparison holding unit
650
provided in the switch
600
makes a comparison among the ERs in every received BRM cell and holds the smallest ER in an ER table
660
. According to a timing control by a timer
680
, the smallest ER being held is notified to a BRM cell generating unit
670
. The BRM cell generating unit
670
generates a BRM cell according to the timing control by the timer
680
. The timer
680
makes a notification toward the BRM cell generating unit
670
and the ER comparison holding unit
650
in every fixed period of time and controls the operation thereof.
The operation of the multi-cast ABR service system shown in
FIG. 6
will be described this time.
FIGS. 7 and 8
are flow charts for use in describing the operation of the system shown in FIG.
6
. With reference to
FIGS. 7 and 8
, the sending terminal
10
sends an FRM cell with the sending rate information [ER
0
] mounted thereon, to the receiving terminals (Step
701
). The FRM cell sent from the sending terminal
10
is broadcast through the switch
600
to all the receiving terminals
41
to
43
. Thus, all the receiving terminals
41
,
42
, and
43
respectively receive the FRM cell. In the switch
600
, the timer
680
starts counting (Step
702
). Thereafter, the timer
680
continues counting to a predetermined value [X] and when the count value becomes [X], the timer
680
notifies it to the ER comparison holding unit
650
and the BRM cell generating unit
670
.
All the receiving terminals
41
,
42
, and
43
, each having received the FRM cell, return each BRM cell with the transferable ER for each receiving terminal
41
,
42
, and
43
mounted thereon, to the sending terminal
10
(Step
703
). The ER [ER
1
] is mounted on the BRM cell as for the receiving terminal
41
, the ER [ER
5
] is mounted on the BRM cell as for the receiving terminal
42
, and the ER [ER
3
] is mounted on the BRM cell as for the receiving terminal
43
. Hereinafter, the description will be made on assumption that the BRM cell
1
sent from the receiving terminal
41
, the BRM cell
2
sent from the receiving terminal
42
, and the BRM cell
3
sent from the receiving terminal
43
would reach the switch
600
in this order.
The BRM cells sent from all the receiving terminals
41
,
42
, and
43
are sent to the ER comparison holding unit
650
, the ERs mounted on the respective BRM cells are compared, and the smallest ER is held in the ER table
660
. The ER comparison holding unit
650
makes a comparison of the ERs of the BRM cells successively received and holds the smaller ER selectively (refer to Steps
706
,
707
,
714
,
715
,
722
, and
723
).
As illustrated in
FIG. 6
, the ER of the BRM cell sent from the re

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