Multiplex communications – Channel assignment techniques – Carrier sense multiple access
Patent
1994-09-26
1997-11-18
Ton, Dang
Multiplex communications
Channel assignment techniques
Carrier sense multiple access
370461, H04J 302
Patent
active
056895100
DESCRIPTION:
BRIEF SUMMARY
The applicants have filed, on the same day that this application was filed, another copending patent application, Ser. No. 08/307,584, entitled "DATA TRANSMISSION DEVICE FOR RANDOM ACCESS NETWORK, WITH IMPROVED COLLISION RESOLUTION, AND CORRESPONDING METHOD". Because of the technical relationships with the present application, the description and drawings of this other application are incorporated into the present application, now U.S. Pat. No. 5,517,501 issued May 14, 1996.
BACKGROUND OF THE INVENTION
1. Field of the invention
The invention concerns computer networks which allow the exchange of information or "data" between different terminals.
2. Related Art
Such a network conventionally comprises a transmission medium, generally an electrical or fibre 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).
The implementation of such a network, but with the ether as the communication medium, that is to say with transmission by radio waves, poses various problems which the present invention will help to resolve.
SUMMARY OF THE INVENTION
A first aim of the invention is to improve the detection or recognition of collision, when a radio network is involved.
The invention also aims to ensure that all the stations or terminals concerned will have common access to collision information, which is necessary for the consistency of subsequent collision resolution operations.
The invention also aims to ensure correct maintenance of frequency synchronisation between the various terminals connected by radio.
In addition, the invention aims to take account of the special characteristics of radio transmissions, which result in the existence of several pathways over a set of three non-aligned terminals, but the possible preclusion of some of these pathways by obstacles.
In addition, the invention aims to allow indirect transmission of information between two terminals, via one or more intermediate terminals.
The data transmission installation proposed here is of the type comprising at least two data processing terminals (the word "processing" being taken in its most elementary sense). Each terminal is equipped with a network interface, capable of transmitting messages on request, and collecting received messages. This comprises a transmission/reception management device having a collision detector and a means for collision resolution, following recognition of a collision condition. One of the essential functions of this management device is the issuing of instructions confirming transmission or reception to the network interface.
According to a first aspect of the invention, each terminal has a multi-directional radio transmission/reception device (effective in several directions, but not necessarily omni-directional), with: transmission of messages to be exchanged, and controlled in accordance with the said confirming instructions, and
In response at least to the start of an instruction confirming transmission, the auxiliary transceiver, capable of rapid transmission/reception switching, operates in rapidly alternating transmission/reception, according to a chosen pattern which is peculiar to it (preferably substa
REFERENCES:
patent: 4665519 (1987-05-01), Kirchner et al.
patent: 5040175 (1991-08-01), Tuch et al.
patent: 5418784 (1995-05-01), Ramakrishnan et al.
Jacquet Philippe
Muhlethaler Paul
Inria Institut National de Recherche en Informatique et en Autom
Ton Dang
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