US 4,516,239 AGranted

System, apparatus and method for controlling a multiple access data communications system including variable length data packets and fixed length collision-free voice packets

AssigneeAT&T Bell Laboratories

InventorNicholas F. Maxemchuk

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Abstract

A variation on a carrier sense multiple access/collision detection (CSMA/CD) system protocol for local area, packet, random access, broadcast networks is disclosed for effectively servicing both voice and data traffic. When the instant method is used, a mix of periodic voice traffic and aperiodic data traffic can be transmitted on a channel without the voice packets colliding. Also, an upper bound on the delay experienced by the periodic traffic can be established. In the instant method, aperiodic sources contend for a channel as in conventional CSMA/CD networks. However, unlike conventional protocols, periodic sources transmit a preempt field, responsive to which aperiodic sources terminate transmission. Also unlike conventional protocols, a periodic "time slot" may be delayed up to one packet transmission time when the network is busy transmitting aperiodic data. Additional information can be transmitted in an overflow field so that a receiver can supply periodic samples at regular intervals with the advantageous result of obviating discontinuities in a reconstructed analog speech waveform. Also unlike conventional CSMA/CD networks, the system capacity can be fully utilized by periodic sources. Still further, the instant method contemplates a system with no centralized control to assign "time slots" or to reallocate capacity between periodic and aperiodic sources. In addition, movable time slots allow timing discrepancies between periodic sources to be tolerated.

Claims8

Dependent claims

A method for controlling digital signals in a communications system, said system including a communications channel, a plurality of station sources, at least two of said sources being adapted to be coupled to said channel, said method including the steps of

receiving signals from said channel,
responsive to said received signals, detecting the busy/idle status of said channel,
responsive to said channel being detected as busy waiting for an idle channel and
at least one of said station sources is a station source of a first kind and at least one other of said station sources is a station source of a second kind, and
said method further comprises the steps of:
responsive to said channel being detected as idle, acquiring access to said channel;
responsive to acquiring said channel, transmitting a packet from a first source to a second source on said channel;
responsive to said packet being from a first source of said first kind, said transmitting step further including the steps of
including a preempt field in said packet, said preempt field comprising a delay signal, said delay signal lasting a predetermined time interval, and
continuing to transmit said packet without listening to said channel;
and
responsive to said packet being from a first source of said second kind, said transmitting step further including the step of
listening to said channel while continuing to transmit said packet, said listening step further comprising the steps of
upon detecting a collision while listening to said channel, terminating any transmitting from said first source of said second kind within a time interval that is no more than the predetermined time interval of said preempt field delay signal, and
responsive to said terminating, waiting for said channel to become idle before retransmitting said packet.

12 more elements

Dependencies are inferred from the claim text.