Multiplex communications – Wide area network – Packet switching
Patent
1992-10-15
1995-05-16
Safourek, Benedict V.
Multiplex communications
Wide area network
Packet switching
H04J 302
Patent
active
054167752
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for transmitting information in the form of data packets in a communications network which comprises two unidirectional transmission channels of opposing transmission direction and stations or access units each of which is linked to both of those two transmission channels. Information moves, under the control of clock signals, respectively from the first to the last access unit over a first transmission channel and from the last to the first access unit over a second transmission channel. Successive time slots are generated which always comprise the same predetermined number of clock signal cycles. In each of these time slots a number of information bits can be written. An access unit which is ready to transmit a data packet places a request bit in a time slot in the transmission channel other than the channel in which the data packet needs to be transmitted to reach its destination. Each access unit records the number of request bits which have passed through and beyond it and the number of request bits still to be transmitted by that access unit.
BACKGROUND AND PRIOR ART
A method of this type is described in European Patent Application EP-A-0203165 under the name QPSX protocol, but in the meantime it has become better known in specialist circles by the name DQDB protocol, which name will also be used for it hereinafter.
According to the DQDB protocol, use is made of two transmission channels, in general data buses, with mutually opposing communication directions. A series of successive access units is connected to the two buses. The information to be transmitted is transferred from temporary storage to time slots of a fixed size (53 bytes).
Access units which have data to transmit select one of the two buses according to the destination of the data, for example. The data packets to be transmitted are dispatched via the time slots passing by in the chosen direction after first completing an access protocol relating to time slots for each time slot involved. This access protocol proceeds as follows:
An access unit which receives a report from outside the transmission system above described for transmission of a data packet in the transmission direction of bus 1 places, as soon as this is possible, a bus 1 request bit for a time slot (hereinafter referred to simply as a request bit) in a predetermined section of a time slot on bus 2. By this means the access units downstream in the transmission direction of bus 2, therefore upstream in the transmission direction of bus 1, are informed that a packet is ready for transmission on bus 1 and that these access units must allow an empty time slot to pass by on bus 1 for that packet. In this way, as it were, a distributed FIFO buffer is constructed for each bus. For this mechanism a so-called request counter, a so-called countdown counter and a so-called still to be transmitted or untransmitted request counter are provided for each bus in each access unit.
If an access unit has nothing to transmit, the passage of a request bit on bus 2, for example, results in the content of its request counter belonging to bus 2 being increased by one (incremented). The bus 2 request counter in every access unit downstream on bus 2 thus contains an indication of the number of requests for transmission slots on bus 1. Conversely, the request counter for bus 1 in every access unit downstream on bus 1 contains an indication of the number of requests for transmission slots on bus 2. Each empty time slot, i.e. each possibility for transmitting data, which passes by an access unit on bus 1 results in the content of the request counter of bus 2 at the same access unit being reduced by one (decremented), and vice versa regarding bus 2 and bus 1.
In the following discussion of what happens when an access unit does have a packet to transmit, the term "the relevant access unit" means a particular access unit taken as an example for the purpose of the explanation.
When the relevant access unit has received data for transmission on bus 1, the content of the
REFERENCES:
patent: 4977557 (1990-12-01), Phung et al.
patent: 5001707 (1991-03-01), Kositpouboon et al.
patent: 5038347 (1991-08-01), Courtois
patent: 5081622 (1992-01-01), Nassehi et al.
patent: 5111456 (1992-05-01), Limb
patent: 5115430 (1992-05-01), Hahne et al.
patent: 5124981 (1992-06-01), Golding
patent: 5157657 (1992-10-01), Potter et al.
R. M. Newman et al., "The QPSX Man", Apr. 1988, pp. 20-28, IEEE Communications Magazine, vol. 26, No. 4.
H. Ohnishi et al., "ATM Ring Protocol and Performance", Jun. 1989, pp. 394-398, IEEE International Conference on Communications, Boston, Mass.
Koninklijke PTT Nederland NV
Nguyen Chau T.
Safourek Benedict V.
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