Selective congestion control mechanism for information networks

Details Selective congestion control mechanism for information networks Selective congestion control mechanism for information networks

1996-04-17

1998-06-16

Chin, Wellington

Multiplex communications

Data flow congestion prevention or control

Flow control of data transmission through a network

370235, H04J 314

Patent

active

057682585

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention concerns a congestion control mechanism for switch-based information networks. The Asynchronous Transfer Mode (ATM) of these networks can be introduced also for local area networking. A Local Area Network (LAN) predominantly has to cope with nonreserved bandwidth traffic, which is inherently unpredictable and very loss-sensitive. This application necessitates a congestion control mechanism that reacts immediately upon detection of a traffic bottleneck by temporarily holding back the data traffic that is to pass the bottleneck. Other traffic should be influenced as little as possible. The present invention discloses a selective congestion control mechanism which fulfills these needs and which is generally applicable in switch-based networks. It may be used in ATM switches and other types of switches.


BACKGROUND OF THE INVENTION

Communication in switch-based ATM networks is connection-oriented and all ATM cells belonging to a connection follow the same path by swapping their routing labels at the input port of each switch. (See R. Handel, M. N. Huber, "Integrated Broadband Networks: An Introduction to ATM-Based Networks," Addison-Wesley Publishing Company, 1991, and W. E. Denzel. A.P.J. Engbersen, I. Iliadis, G. Karlsson, "A Highly Modular Packet Switch for Gb/s Rates," International Switching Symposium, Yokohama, Japan, Oct. 1992, pp 236-240.) Thus, the actual routing decisions take only place during connection set-up, and routing is not considered as a critical issue in the ATM environment. In contrast, congestion control is already today considered to be one of the difficult challenges that must be solved. This is particularly true for the envisioned LAN emulation service.
The principle of throttling or holding back cells selectively is quite natural and in some sense it has been reported since the early days of packet switching. Still, only recently the advance in technology has made it possible to realize this idea economically and in a more sophisticated manner. Recent studies in this direction have been reported in H. J. Chao, "A General Architecture for Link-Layer Congestion Control in ATM Networks", International Switching Symposium, Yokohama, Oct. 1992, pp. 229-233; J. Cherbonnier. j.-Y. Le Boudec "A GFC Protocol for Congestion Avoidance in the ATM Connectionless Service," EFOC/LAN 92, Paris, Jun. 1992, paper LAN/150, pp. 305-309; P. O. Mishra. H. Kanakia, "A Hop-by-Hop Rate-Based Congestion Control Scheme", COMM'92, pp. 112-123. The Mishra et al reference; compares the behavior of a hop-by-hop congestion control mechanism with an end-to-end control mechanism. Simulation results clearly show its superiority over the slow reacting end-to-end control in terms of higher throughput, lower delay, smaller loss probability, and smaller buffer requirements. The Chaos reference shows the use of a dedicated Trafic Regulator & Scheduler (TRS) at each output port. If a switch's queue is congested, its TRS can send control information backwards to some previous nodes along the paths to produce selective back-pressure. A TRS uses back-pressure signals from a congested node to selectively throttle traffic by reducing the average transmission rates of congested routes.
In a data environment, congestion cannot be resolved by discarding cells. Discarding cells owing to buffer overflow is a practice that originates from the telecommunication culture with a strong bias to real-time voice and video connections, which all require reserved bandwidth. Whereas for real-time applications, discarded cells are annoying for the user, but have no negative effect on the network. However discharging a single cell belonging to a data frame triggers definitely all the frame cells to be retransmitted, so that the network may become flooded by additional traffic without an increase in user throughput. Thus, discarding cells belonging to nonreserved traffic potentially consumes a significant part of the network capacity without any benefit.
It is a general object of this invention to avoid the

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Gerla et al, "Congestion Control in Interconnected LANs," 1988 pp. 72-76.

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