Priority access for real-time traffic in contention-based networks

• US 5,982,779 A
• Filed: 09/04/1997
• Issued: 11/09/1999
• Est. Priority Date: 05/28/1997
• Status: Expired due to Fees

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Krishnakumar, Anjur Sundaresan, Sobrinho, Joao Luis
• Primary Examiner(s): Nguyen, Chau
• Assistant Examiner(s): Wolkow, Frederic D.
• Application Number:
  US08/923,302
• Time in Patent Office: 796 Days
• Field of Search: 370/447, 370/445, 370/448, 370/461, 370/431, 340/825.5, 340/825.07, 340/825.08
• US Class Current: 370/447
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04L 47/13 in a LAN segment, e.g. ring or bus
• CPC Class Codes: H04L 47/2416 Real-time traffic
• CPC Class Codes: H04L 47/26 using explicit feedback to the source, e.g. choke packets
• CPC Class Codes: H04L 65/1101 Session protocols
• CPC Class Codes: H04L 9/40 Network security protocols

Abstract

A contention-based network which allows real-time traffic to be assembled into multiple linked-list chains. A time separation is enforced between the various multiple chains, which are limited to a predetermined maximum number of stations that each can have in order to allow non-real-time stations to obtain timely access to the medium. Ones of the multiple chains may also be joined into a single chain. Blackburst contention is used to enable a chain to be reconstituted robustly from non-anticipated interruptions, such as the failure of one of its stations.

Claims

1. Apparatus comprising

a plurality of stations including a plurality of stations of a first type and a plurality of stations of a second type, and

a communications medium,

each of said plurality of stations being adapted to non-pre-emptively contend with one another for access to said communications medium in order to be able to transmit a data packet to another one of said plurality of stations over said communications medium,

each of said first-type stations being arranged to terminate the transmission of a packet that it is then transmitting over said communications medium, and entering a back-off mode, upon the occurrence of a collision of that packet with another packet being transmitted over said communications medium,

at least ones of said second-type stations comprising a chain of stations which, in each one of succession of access periods, transmit respective packets on said medium upon the completion of the transmission of the packet by a predetermined prior station of said chain and in a way which precludes any others of said plurality of stations from transmitting on said medium until each station of said chain has transmitted its packet, each of the stations of said chain having an associated expected access time for initiating the transmission of its packet, and in the event that said expected access time for any particular station of the chain occurs before said prior station has completed the transmission of its packet,

each such particular station a) initiating the transmission of a packet if said medium then appears to be idle said packet including an initial portion which includes a first signal of sufficient duration to ensure that any of said first type stations that are then transmitting enter said backoff mode and further includes a blackburst signal of a duration which is a function of said expected access time, and b) terminating said blackburst signal and continuing with the transmission of said particular station'"'"'s packet only if the blackburst signal transmitted by said particular station becomes the only blackburst signal being transmitted on said medium,

whereby said second-type stations obtain priority access to said medium relative to said first type stations and whereby each of said second-type stations obtains access to said medium in accordance with said access priority.

2. The invention of claim 1 wherein the packets transmitted by said first type of station comprise non-real-time data and the packets transmitted by said second type of station comprise real-time data.

3. The invention of claim 1 wherein in each access period each of the stations of said chain, defines the expected access time for that station for the subsequent access period.

4. The invention of claim 3 wherein said expected access time is defined via the setting of a timer which is to expire at said expected access time.

5. The invention of claim 1 wherein said duration of said blackburst signal is directly proportional to the length of the time interval between said expected access time and the initiation of said blackburst signal.

6. A communications station for use in a contention-based network which includes a communications medium and a plurality of communications stations including said communications station, said network being one in which, in each one of succession of access periods, the stations in a chain comprising ones of said plurality of stations, including said communications station, transmit respective packets on said medium upon the completion of the transmission of the packet by a predetermined prior station of said chain and in a way which precludes any others of said plurality of stations from transmitting on said medium until each station of said chain has transmitted its packet, each of the stations of said chain having an associated expected access time for initiating the transmission of its packet,

said communications station being operative to initiate the transmission of a packet in the event that said expected access time occurs before said prior station has completed the transmission of its packet and the medium appears to be idle, said packet including an initial portion which includes a blackburst signal of a duration which is a function of said expected access time,

said communications station being further operative to terminate said blackburst signal and continuing with the transmission of its packet only if the blackburst signal transmitted by said communications station becomes the only blackburst signal being transmitted on said medium.

7. The invention of claim 6 wherein in each access period, said communications station defines the expected access time for that station for the subsequent access period.

8. The invention of claim 7 wherein said expected access time is defined via the setting of a timer which is to expire at said expected access time.

9. The invention of claim 7 wherein the packets transmitted by said communications station contains real-time traffic.

10. The invention of claim 6 wherein said duration of said blackburst signal is directly proportional to the length of the time interval between said expected access time and the initiation of said blackburst signal.

11. A method for use in an network which comprises

a plurality of stations including a plurality of stations of a first type and a plurality of stations of a second type, and

a communications medium,

each of said plurality of stations being adapted to non-pre-emptively contend with one another for access to said communications medium in order to be able to transmit a data packet to another one of said plurality of stations over said communications medium,

each of said first-type stations being arranged to terminate the transmission of a packet that it is then transmitting over said communications medium, and entering a back-off mode, upon the occurrence of a collision of that packet with another packet being transmitted over said communications medium,

at least ones of said second-type stations comprising a chain of stations which, in each one of succession of access periods, transmit respective packets on said medium upon the completion of the transmission of the packet by a predetermined prior station of said chain and in a way which precludes any others of said plurality of stations from transmitting on said medium until each station of said chain has transmitted its packet, each of the stations of said chain having an associated expected access time for initiating the transmission of its packet, and in the event that said expected access time for any particular station of the chain occurs before said prior station has completed the transmission of its packet,

the method comprising the steps, performed by said particular station, of

initiating the transmission of a packet if said medium then appears to be idle, said packet including an initial portion which includes a first signal of sufficient duration to ensure that any of said first type stations that are then transmitting enter said backoff mode and further includes a blackburst signal of a duration which is a function of said expected access time, and

terminating said blackburst signal and continuing with the transmission of said particular station'"'"'s packet only if the blackburst signal transmitted by said particular station becomes the only blackburst signal being transmitted on said medium.

12. The invention of claim 11 wherein said duration of said blackburst signal is directly proportional to the length of the time interval between said expected access time and the initiation of said blackburst signal.

13. A method for use in a contention-based network which includes a communications medium and a plurality of communications stations, said network being one in which, in each one of succession of access periods, the stations in a chain comprising ones of said plurality of stations transmit respective packets on said medium upon the completion of the transmission of the packet by a predetermined prior station of said chain and in a way which precludes any others of said plurality of stations from transmitting on said medium until each station of said chain has transmitted its packet, each of the stations of said chain having an associated expected access time for initiating the transmission of its packet,

said method being carried out in at least one of the stations of said chain in the event that said expected access time occurs before said prior station has completed the transmission of its packet, said method comprising the steps of

initiating the transmission of said one station'"'"'s packet if the medium appears to be idle, said packet including an initial portion which includes a blackburst signal of a duration which is a function of said expected access time, and

terminating said blackburst signal and continuing with the transmission of said one station'"'"'s packet only if the blackburst signal transmitted by said one station becomes the only blackburst signal being transmitted on said medium.

14. The invention of claim 13 wherein in each access period, each of the stations of said chain, defines the expected access time for that station for the subsequent access period.

15. The invention of claim 14 wherein said expected access time is defined via the setting of a timer which is to expire at said expected access time.

16. The invention of claim 14 wherein the packets transmitted by the stations of said chain contain real-time traffic.

17. The invention of claim 13 wherein said duration of said blackburst signal is directly proportional to the length of the time interval between said expected access time and the initiation of said blackburst signal.

18. The invention of claim 13 wherein said plurality of stations include real-time stations whose packets include real-time data and further include non-real-time stations whose packets include non-real-time data, the stations of said chain comprising ones of said real-time stations.