Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Patent
1996-09-24
1999-03-30
Olms, Douglas W.
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
370235, 370412, H04J 116, H04J 314, H04L 1228, H04L 1256
Patent
active
058897623
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/FI94/00534, filed Nov. 29, 1994.
The invention relates to a method according to the preamble of appended claim 1 for congestion management in a frame relay network, and to a subscriber node according to the preamble of appended claim 3.
Congestion means a situation in which the number of transmission requests exceeds the transmission capacity at a certain network point (called a bottle-neck resource) at a specific time. Congestion usually results in overload conditions, as a result of which the buffers overflow, for instance, and so packets will be retransmitted either by the network or the subscriber. The function of congestion management (CM) is to maintain a balance between the transmission requests and the transmission capacity so that the bottle-neck resources operate on an optimal level, and the subscribers are offered service in a way that assures fairness.
Congestion management can be divided into congestion avoidance (CA) and congestion recovery (CR). Congestion avoidance methods aim at preventing the occurrence of congestion in the network by dynamically adjusting the bandwidth of the subscribers in accordance with network congestion conditions and/or by altering the network routing so that part of the traffic load of the bottle-neck resources is shifted to idle resources. The purpose of recovery methods, in turn, is to restore the operation of the bottle-neck resources to an optimal level if the avoidance methods have failed to prevent the occurrence of congestion.
The frame relay (FR) technique is a packet-switched network technique used for the transmission of frames of varying length in place of the packet-switched network connections presently in use. The protocol (X.25) applied generally in the present packet-switched networks requires plenty of processing and the transmission equipment is expensive, as a result of which the speeds also remain low. These matters are due to the fact that the X.25 standard was developed when the transmission connections used were still rather prone to transmission errors. The starting point of the frame relay technique was a considerably lower transmission line error probability. It has therefore been possible to discard a number of unnecessary functions in the frame relay technique, which makes the delivery of frames rapid and efficient. The Frame Mode Bearer Service is described generally in CCITT recommendation I.233 (Reference 1) and the associated protocol in recommendation Q.922 (Reference 2). Congestion in an FR network and congestion management mechanisms are described in CCITT recommendation I.370 (Reference 3). For a more detailed description of the FR technique, reference is made to An Overview of Frame Relay Technology, Datapro Management of Data Communications, McGraw-Hill Incorporated, April 1991, (Reference 4) as well as the above-mentioned recommendations.
As a last resort in cases of extremely severe congestion in a frame relay network, frames can be discarded. Situations of this kind arise when both the transmission capacity of the network and the buffering capacity of a single node are exceeded. In the congestion management mechanisms presently used, frames are discarded almost randomly both on the periphery of the network (at subscriber nodes) and in the middle of the network (at trunk nodes). A frame is discarded if it cannot be buffered due to lack of space, or if the fill rate of the buffer is sufficiently high and the frame contains an indication which allows it to be discarded in the event of congestion, for instance. Nothing is done to affect the buffer itself; it continues to be emptied to the data link as normal. If the frame is not discarded until at a congested node, the other resources of the network are loaded in vain. The frame must be switched through the network up to the point where it is discarded, i.e. to the congested node, which means wasting the resources.
The object of the present invention is to obviate the drawback described above and to provide a new
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Fehlmann Richard
Kasslin Mika
Laiho Mikko
Matkaselka Jorma
Olkkonen Mikko
Nokia Telecommunications Oy
Olms Douglas W.
Vincent David R.
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