Multiplex communications – Wide area network – Packet switching
Patent
1994-09-27
1996-05-14
Safourek, Benedict V.
Multiplex communications
Wide area network
Packet switching
370 856, H04L 12413
Patent
active
055175015
DESCRIPTION:
BRIEF SUMMARY
The invention concerns computer networks which allow the exchange of information or "data" between different terminals.
Such a network conventionally comprises a transmission medium, generally an electrical or fiber optic cable. Stations or terminals are connected at various places on this cable, this connection being made through a "network interface".
It is essential for the terminals to understand each other, despite their multiplicity. In some computer networks, a rule (multiplexing, token) is determined for this purpose, in accordance with which no more than one of the terminals may transmit over the communication medium at a given moment. Another technique permits "random access" to the network, that is to say several terminals may transmit at the same time. One consequence of this multiple access is that "collisions" may occur, and it will then be necessary to resolve them.
The ETHERNET (registered trade mark) network, governed by the standard known as IEEE 802.3, is of the random access type. The network management protocol is of the multiple access carrier sensing type with collision detection, or CSMA/CD (Carrier Sense Multiple Access with Collision Detection).
One of the essential features of such a network is its ability to effect a "collision resolution" rapidly. This is because, when a transmission has given rise to a collision, it is necessary to recommence transmission. This has the direct effect of increasing the instantaneous need for transmission. As a result, if a multiple access channel is operating with very high traffic, the collision resolution may take correspondingly longer, and consequently the waiting time for a successful transmission correspondingly more protracted.
The Applicant has moreover observed that at least two types of data traffic can be distinguished:
a) data coming from sensors in real time, for example voice (telephony) or video (image);
b) exchanges of files or knowledge tables coming from bulk storage, which are pure data packets.
The Applicant has also observed that the constraints which are applied to the exchange of these different types of data are fairly divergent.
Data coming from sensors in real time are generally fairly heavily redundant. As a result it is possible to accept a significant loss rate for these data packets without appreciable degradation of the quality of the data conveyed: it is known for example that voice telephony data, which are highly redundant, may be cut to a great extent without loss of intelligibility. On the other hand, telephony data packets must be carried within strict time periods.
In contradistinction to this, exchanges of file data for example are much less sensitive to transmission times. On the other hand, they are not able to sustain any level of data loss and are very demanding in terms of passband. In addition, they require acknowledgement of reception and flow monitoring protocols, which is not the case with voice data packets for example.
This poses different problems, which the invention is aimed at helping to resolve.
A first aim of the invention is to provide a better collision resolution technique, which increases the efficacy of a multiple access channel.
The second aim of the invention is to allow the use and implementation of priority classes in the operation of this collision resolution technique.
In order to form a computer network from a transmission medium or channel, a device is associated with each data processing terminal, comprising:
a network interface, capable of the transmission/reception of messages over the channel, with monitoring of the channel in order to establish event signals, which selectively represent the detection of the start of a transmission on the channel, the detection of any new collision, and the detection of the return of the channel to the vacant state, and
a transmission/reception management device, for controlling the network interface in accordance with the event signals.
Means are provided, in general in the network interface, to ensure that, in the event of a collision, tr
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Jacquet Philippe
Muhlethaler Paul
Inria Institut National de Recherche en Informatique et en Autom
Safourek Benedict V.
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