Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1998-12-14
2002-11-19
Kizou, Hassan (Department: 2662)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S392000, C370S401000
Reexamination Certificate
active
06483852
ABSTRACT:
FIELD OF THE INVENTION
The field of this invention relates to computer networks enabling exchanges of data and information between units or stations in different networks. Different networks here means either several (at least two) radio networks which can function using different channels and/or protocols, or a combination of at least one radio network and at least one cable network (electrical or optical fibre cables).
BACKGROUND OF THE INVENTION
In the case of a combination of radio and cable networks, mobile stations coexist with fixed stations connected to the cable via connection devices (or bridges), a storage module which stores at least one routing table, and a processing (or switching) module which manages data exchanges according to the routing table.
It is well known that such connection devices (or bridges) are generally provided with network interfaces (one for each network segment), the different network interfaces being able to have parts which are possibly common. In this case, the processing (or switching) module manages the data exchanges at the network interfaces, according to the said routing table.
The invention concerns more particularly the connection devices (or bridges) between at least segments of a so-called “main” network (in which one station has sent a-message intended for at least one other station in the same network) communicating by means of messages provided with a so-called main capsule complying with a protocol based on a first format and at least one segment of at least one “ancillary” network communicating by way of messages provided with an ancillary capsule complying with a protocol based on a second format.
In the following, “encapsulated message” will mean a message consisting of data and a “capsule” containing information peculiar to the format of the network concerned.
In addition, bridge means a device providing the transfer of a message from one network to one or more other networks. Such bridges can be simple repeaters when they are used only for relaying data frames (or packets). However, in certain cases, it may be a question of so-called “intelligent” bridges which can constitute what a person skilled in the art refers to as “spanning trees”. However, under certain operating conditions, such intelligent bridges can momentarily block the transmission of messages, preventing any connection between two subscribers on the same network. This is notably the case when a message is repeated on a (cabled) section, and an intelligent bridge deems that the source of the said message is a fixed station in the section and that it is consequently necessary to filter the messages (or block one transmission direction) for a certain period of time, which prevents access to the said source.
This drawback is particularly inconvenient when a-mobile station (in a radio network) is caused to change (cabled) section in order to communicate with the remainder of the data transmission installation to which it belongs.
This is because, in this type of installation, the mobile and connecting stations (or relays) generally comprise a memory in which there is stored a routing table which enables their processing module to determine the optimum path for reaching the station or stations to which the message which they have just received relates. However, in order to allow the updating of the routing tables, the mobile and connecting stations exchange so-called “service” messages which indicate the movements of the different mobile stations, with respect to each other and relative to sections.
In addition, the bridges receive messages from the mobile stations, which they next transmit over the cable network without any real modification, because the bridges assimilate these mobile stations to fixed stations in the cable network. Consequently, as soon as a mobile station moves, this poses a real problem which may result either in a blockage of a section of network by a bridge; one or more mobile stations no longer being able to communicate with remote stations, or in the impossibility of determining the optimum path which will enable a mobile station to communicate with a remote station. This could occur with “intelligent” bridges.
The aim of the invention is therefore to procure a connection device which does not have the above-mentioned drawbacks.
SUMMARY OF THE INVENTION
To this end it proposes a connection device of the type described in the introduction, in which the processing module comprises a management module able on the one hand to disencapsulate a message received from the said main network (to withdraw its main capsule) so as to extract routing information therefrom, then to compare this information with the stored routing table in order to choose, from amongst the main and ancillary networks, at least one re-sending network segment for the disencapsulated message, and on the other hand to add to the said disencapsulated message, before it is re-sent, a main capsule or a mixed capsule, including a main capsule and an ancillary capsule, depending on whether the re-sending network chosen is the main network or an ancillary network, so as to re-send the thus re-encapsulated message in the segment of the chosen re-sending network.
Thus, by virtue of the connection device (or hybrid station) according to the invention, it is possible to transform several networks independent of each other into a super-network in which the messages can pass from a segment of a main network to another segment of this main network, via a segment of an ancillary network which in some way serves as a “gateway”.
According to another characteristic of the invention, the management module is arranged to add, to the re-encapsulated message to be re-sent, a protocol designating the format of the main network segment from which this message came.
This makes it possible to keep a trace of the (main) network which is the origin of the message to be transmitted, and consequently to inform the routing tables of the hybrid stations (or connection device) about the stations which can be accessed by this network. This is particularly advantageous when, notably, main networks of the same types (or segments of a main network) are isolated from each other, because of their separation or else because of obstacles.
The connection device according to the invention is particularly adapted to the main and ancillary networks respectively of the radio network and cabled network types. The cabled network, allowing higher transmission speeds, can therefore be used as a short-cut. However, the device may also make it possible to connect together segments of radio networks which can function on respective channels which are different or substantially identical.
When the main and ancillary networks are two radio networks functioning on the same channel, but with different protocols, the architecture of their two network interfaces (on the assumption that the interconnection device has one for each network) may at least partially merge into a physical interface with the ether (communication medium).
Naturally, a connection device (or hybrid station) may allow the connection of more than two networks, for example three or four or even more, whether they are all of the radio type or of radio and cabled (mixed) types.
According to yet another characteristic of the invention, the format of a radio network can be chosen from at least the “HIPERLAN” and IEEE 802.11 standards, and the format of a cabled network can be chosen from at least the IEEE 802.3, 802.5 and ANSI.FDDI standards.
The HIPERLAN format is notably described in the publications of the European Standardization Institute (ETSI) and more particularly in the technical standard ETS-300-652.
In the case of IEEE 802.11, the device can be situated at an interface with a distribution system (the terminology in the standard), in the access point and, where applicable, this distribution system can be supported by the same radio interface as the basic service sets BSS (using this same terminology), without necessarily sharing the same channels. Prefer
Jacquet Philippe
Muhlethaler Paul
Inria Institut National de Recherche en Informatique et en Autom
Kizou Hassan
Rabin & Berdo P.C.
Spafford Tim
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