Multiplex communications – Communication over free space – Combining or distributing information via time channels
Reexamination Certificate
1996-09-30
2001-05-22
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication over free space
Combining or distributing information via time channels
C370S443000, C370S449000
Reexamination Certificate
active
06236650
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns methods, devices and systems for sharing a transmission medium between communication means, transmission methods, communication devices and communication systems using them.
In the present document, reference will be made to the following definitions:
“Communication converter”: any interface or digital communication adapter between a medium able to be shared and a medium dedicated to a single communication means, the two transmission media being controlled by different respective access protocols.
“Address”: any information
enabling a destination to recognize itself when a message is sent to it;
enabling a sender to identify himself when he is transmitting a message.
It is known that, in a network between digital communication means which transmit data over the same transmission medium, it is necessary to define a protocol controlling access to the medium, which organises the said access. The performance of the network in the transmission of digital data between the communication means depends on the efficacy of the protocol.
Access control protocols attempt to respond both:
to a sending access constraint: it is necessary for the communication means which have data to transmit over the said medium to have sufficient opportunity to access the network in order to transmit them in their entirety; and
to a transmission constraint: it is necessary for the data sent by a communication means over the said medium to arrive at their destination in their entirety.
Simultaneously meeting these two constraints raises serious difficulties in the prior art. This is because, as will be seen, the known protocols do not meet one or other of these two constraints in certain cases, or meet them at the cost of a serious reduction in their performance.
In this regard, it will be noted that, when the sending access constraint and the transmission constraint are met, the two criteria traditionally used for measuring the said performance are on the one hand the maximum data transmission rate which the communication means can, by themselves, transmit on average during a given period and, on the other hand, the transmission time between the moment when the data are ready to be transmitted by a communication means and the moment when they have been entirely received by their destination and can therefore be used by the latter.
A first protocol is known which may be called “full competition”, according to which each communication means is authorised to send when the transmission medium is available. When two communication means effect simultaneous sending of data, a collision occurs which may result in the signals conveyed by the shared medium not being usable.
The existence of these collisions in not insignificant numbers has the consequence that the transmission medium is unnecessarily occupied and that the data transmitted over the medium by certain communication means may never reach their destination, the transmission constraint not being met if there is no retransmission of the said data. When this constraint is met, it has been found that the maximum data transmission rate is approximately one third of the maximum theoretical rate of the medium for a properly sized network.
In addition, the full competition protocol is of interest only in a cabled network since the collisions which occur on a medium consisting of an electrical link are easily detected by each networked communication means or at least by a central means. On the other hand, in a wireless network, for example with a radio transmission medium, a networked communication means can detect collisions between the data transmission signals which it sends and those sent by another communication means only at the cost of techniques which are expensive and/or tricky to implement. It is then necessary for the communication means which has received data from another communication means to transmit in return a so-called “acknowledgement” message indicating the correct reception of the said data. An even more appreciable decrease in the said maximum rate results. It is therefore highly desirable to reduce the risk of collisions as far as possible.
A second access management protocol is known, referred to as a “polling centralised control protocol”. According to this protocol, a central networked communication means distributes, to communication means, authorisations to send over the shared transmission medium, following a predetermined order. Each networked communication means which has data to transmit over the shared transmission medium waits until it receives an authorisation to send which is intended for it, before sending.
A third protocol controlling access to a shared transmission medium is also known, of the TDMA type (time division multiple access), in which the communication means are able to transmit only in a time slot allocated to them periodically in a cyclic functioning.
Whatever the protocol it is known that, in a network, communication means may have nothing to send or else be active, but with an activity limited to standby during which they wait until they receive instructions to transmit data. In a network functioning according to a polling protocol or according to a protocol of the TDMA type, the authorisations to send or the time slots which are respectively allocated to the communication means which have nothing to send are wasted since they do not give rise to the transmission of data. This loss is all the greater since, on certain media, notably radio ones, the synchronisation time between a sending communication means and a destination is very long. It turns out therefore that a large number of communication means with a nil transmission rate unnecessarily increases the transmission time for the communication means which have data to transmit. Finally, the more the communication means are liable to have large variations in their traffic, the greater this loss.
It will be noted that, because of this, the reduction in the maximum data transmission rate on the medium is very high. In addition, the higher the number of communication means connected to the shared transmission medium, the more the maximum rate decreases.
Moreover, when one of the networked communication means has, for a relatively long period, a flow of data to be transmitted over the medium which is greater than the available rate resulting from the authorisations to send, or from the time slots, allocated to it, it is as a result impossible for this means to transmit all its data over the medium. The sending access constraint referred to above is not met, in this case, neither by the polling protocol nor by the TDMA protocol. When this constraint is met for temporarily high rates, this occurs at the cost of an increase in the total data transmission time, which gives rise to a drop in performance for the network.
In summary, the full competition protocols have a high performance at low rates but do not allow high rates. On the other hand, polling and time division protocols have a high performance at high rates, but for all rates the transmission time is high since each communication means waits until other communication means have had an opportunity to transmit before doing so, and this is all the more marked as the total number of communication means increases.
In addition, the polling protocol requires the identification of the communication means which are liable to send prior to the personal allocation of an authorisation to send.
SUMMARY OF THE INVENTION
The present invention aims, in general terms, to provide a solution to one or other or both of the following two technical problems:
on the one hand proposing a protocol which profits from the advantageous performance of polling protocols and full competition protocols, minimising the effect of their drawbacks, whilst meeting the transmission and sending access constraints;
on the other hand making it possible to identify unidentified communication means liable to send over the shared medium.
In particular, the present invention sets out to achieve t
le Dantec Claude
Tannhauser Falk
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hyun Soon-Dong
Nguyen Chau
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