Multiplex communications – Data flow congestion prevention or control
Reexamination Certificate
1998-03-26
2001-03-27
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Data flow congestion prevention or control
C370S395430, C370S468000, C709S235000
Reexamination Certificate
active
06208619
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a packet data flow control method and device for a network comprising one or a plurality of packet exchanges that respectively accommodate a plurality of communication terminals in which point-to-multipoint communication or point-to-point communication is performed, and more specifically relates to a packet data flow control method and device whereby communication can be effectively implemented by narrowing of transmission bandwidth or drops in the transmission rate caused by local congestion by means of buffers provided in the packet exchanges.
2. Description of the Related Art
With development of an “information society”, networking of communications continues in progress and LANs (Local Area Networks), of which examples are Ethernets or FDDIs (Fibre Distributed Data Interfaces) are becoming commonplace. Such conventional LANs efficiently implemented simultaneous transmission or multicast transmission, which are important for CL (Connectionless) communication, by taking advantage of the feature of shared media.
On the other hand, in recent years, ATM (Asynchronous Transfer Mode) has attracted attention as a system for implementing multimedia communication, and methods are being studied of implementing the CL communication on a network constructed in ATM.
However, ATM is basically a connection type communication system in which communication is performed after negotiation with the remote party and unlike the conventional shared media type LAN it is difficult to implement multicast transmission or simultaneous transmission.
In particular, in the ABR (Available Bit Rate) service that is recently being studied by the ARM forum which is a de facto standard organisation, the packet data flow control is even more difficult. This is because in the ABR service, with the object of increasing reliability, packet data flow control is performed between a sending terminal constituting the root of point-to-multipoint connection (hereinbelow referred to as pump connection) and the receiving terminals constituting the leaves.
FIG. 7
is a diagram given in explanation of packet data flow control relating to an ABR service that is currently being studied by the ATM forum, showing an operation image in an ATM network when packet data flow control represented by ABR is performed.
FIG. 7
assumes that the connection is a point-to-point connection (hereinbelow called a p-p connection) and that the flow control is implemented in accordance with a congestion indication from a terminal where congestion has occurred. Terminals
10
-
1
,
10
-
2
in this network may be considered as repeaters for connection to networks other than ATM.
In
FIG. 7
, a sending terminal
10
-
1
effects communication with a destination terminal
10
-
2
by setting up a p-p connection through the network connecting a plurality of ATM exchanges
20
-
1
,
20
-
2
,
20
-
3
. When sending terminal
10
-
1
has data that it wishes to send to destination terminal
10
-
2
, it converts the data to the form of cell (data cell) and sends the data cell to destination terminal
10
-
2
and also sends on the same connection a congestion notification cell
50
(see FIG.
9
), to be described, at intervals of a prescribed number of cells that is determined at the time of connection set-up.
These congestion notification cells
50
, just like the data cells are sent to destination terminal
10
-
2
via ATM exchanges
20
-
1
,
20
-
2
,
20
-
3
and are then returned by the destination terminal
10
-
2
so that they are finally sent back to sending terminal
10
-
1
. That is, congestion notification cells
50
flow in a loop.
Any ATM exchange
20
-
1
,
20
-
2
,
20
-
3
or destination terminal
10
-
2
that is on the way to receive the congestion notification cell
50
, if it is in an overloaded condition, sets the congestion indication bit (CI bit) of the incoming circulating congestion notification cell
50
. And if it is in normally-loaded condition it transfers the congestion notification cell as it is without modification.
If congestion is indicated by the congestion notification bit of a received congestion notification cell
50
, sending terminal
10
-
1
lowers the transmission rate by a prescribed amount and, if congestion is not indicated, raises the transmission rate by a prescribed amount within the bit rate range specified at the time of the connection set-up.
In the example of
FIG. 7
, congestion occurs at ATM exchange
20
-
2
and as a result the congestion notification bit is set at ATM exchange
20
-
2
(i.e. CI is made=1), thereby notifying sending terminal
10
-
1
of the congestion.
FIG. 8
shows another example of flow control typified by ABR in an ATM network. While in the network of
FIG. 7
, the transmission rate is controlled in accordance with a congestion indication from the terminal where congestion occurred, in the network of
FIG. 8
, the terminal where congestion was generated is made to explicitly indicate its allowable transmission bandwidth and the transmission rate is controlled in accordance with the explicitly indicated allowable transmission bandwidth.
In the network of
FIG. 8
, any ATM exchange
20
-
1
,
20
-
2
,
20
-
3
or destination terminal
10
-
2
that is on the way to receive the congestion notification cell
50
, if it is in normally loaded condition, transfers the congestion notification cell
50
as it is without modification and, if it is in overloaded condition, records explicitly the allowable transmission bandwidth that it is capable of receiving (i.e. the Explicit Rate: ER) in the incoming circulating congestion notification cell
50
before returning it to sending terminal
10
-
1
.
Also, in the same network, as another method of explicitly indicating the allowable transmission bandwidth, it may be so arranged that any ATM exchange
20
-
1
,
20
-
2
,
20
-
3
or destination terminal
10
-
2
that is on the path within the network itself issues a congestion notification cell
50
as a backward explicit congestion notification cell (BECN) and sends this in the direction of the sending terminal.
If an allowable transmission bandwidth is indicated by a received congestion notification cell
50
, sending terminal
10
-
1
lowers the transmission rate to this explicitly indicated transmission rate and, if congestion is not indicated, raises the transmission rate by a prescribed amount within the range of the peak transmission rate specified at the time of connection set-up
In the example of
FIG. 8
, congestion occurs at ATM exchange
20
-
2
as a result of which the congestion indicating bit is set by ATM exchange
20
-
2
(CI=1) and the allowable transmission bandwidth is set to (ER=xx) and sending terminal
10
-
1
is thereby notified of congestion. It should be noted that, in the example shown in this Figure, if a backward explicit congestion notification cell as mentioned above is employed, a flag to indicate that the cell in question is such a cell is set (BECN=1) so as to make it possible to identify these cells.
FIG. 9
shows the format of the congestion notification cell
50
used in the congestion control discussed above. Congestion notification cell
50
comprises at least ATM cell header
501
, protocol ID field
502
, DIR field
503
that indicates the direction of flow of the cell (towards the destination terminal or towards the sending terminal), BN field
504
that indicates whether the cell is a backward explicit congestion notification cell or not, CI field
505
that gives the congestion indication, ER field
507
for explicitly indicating allowable bandwidth, and CCR field
508
for indicating the current transmission rate. The Res. fields
506
,
509
provided in addition to these in the above format serve as reserves. However, a value is not necessarily set in the ER field
507
but this is employed if a terminal
10
or ATM
20
where congestion has occurred wishes to suddenly lower the transmission rate.
In the ATM cell header
504
is entered a VC
Finnegan Henderson Farabow Garrett & Dunner
Ho Duc
Hsu Alpus H.
Kabushiki Kaisha Toshiba
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