Local area network packet protocol for combined voice and data transmission

• US 4,581,735 A
• Filed: 05/31/1983
• Issued: 04/08/1986
• Est. Priority Date: 05/31/1983
• Status: Expired due to Term

• Current Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: AT&T, Inc.
• Inventors: Limb, John O., Flamm, Lois E.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Kuntz, Curtis
• Application Number:
  US06/499,291
• Time in Patent Office: 1,043 Days
• Field of Search: 370/85, 370/60, 370/94, 370/110.1, 370/16, 370/88, 340/825.5
• US Class Current: 370/389
• CPC Class Codes: H04L 12/64 Hybrid switching systems

Abstract

In order to control the transfer of packets of information among a plurality of stations, the instant communications system, station and protocol contemplate first and second oppositely directed signal paths. At least two stations are coupled to both the first and the second signal paths. A station reads one signal from a path and writes another signal on the path. The one signal is read by an arrangement which electrically precedes the arrangement for writing the other signal. Packets are transmitted in a regular, cyclic sequence. A head station on a forward path writes a start cycle code for enabling each station to transmit one or more packets. If a station has a packet to transmit, it can read the bus field of a packet on the forward path. Responsive thereto, a logical interpretation may be made as to whether the forward path is busy or is not busy. If the path is not busy, the packet may be written on the path by overwriting any signal thereon including the busy field. If the path is busy, the station may defer the writing until the path is detected as not busy.

In order to accommodate different types of traffic, the head station may write different start cycle codes. For example, a start-of-voice code may enable stations to transmit voice packets; a start-of-data code may enable stations to transmit data packets, etc. for the different types of traffic. Further, the start cycle codes may be written in a regular, e.g., periodic, fashion to mitigate deleterious effects, such as speech clipping. Still further, the last station on the forward path may write end cycle codes in packets on a reverse path for communicating control information to the head station. Responsive to the control information, the head station may modify the cycle to permit the respective stations to, for example, transmit more than one packet per cycle or to vary the number of packet time slots, which are allocated to each of the different types of traffic.

Claims

1. A method for controlling digital signals in a communications system, said system including a plurality of stations, at least two of said stations being coupled to first and second separate, independent, unidirectional and oppositely directed signal paths, said method including the steps of writing signals on either of said paths and reading signals from either of said paths and characterized in that said method further comprises the step of:

writing a first start cycle code in a predetermined field of a packet on a forward one of said paths, said first start cycle code being written by a head station and said first start cycle code for identifying a first type of traffic which may be written by a station down the line from said head station relative to said forward path in a packet on said forward path.

2. The method defined in claim 1 further comprising the steps of:

reading said first start cycle code by a first station on said forward path and down the line from said head station relative to said forward path; and

responsive to said first read start cycle code, initializing said first station for writing said first type of traffic identified by said start cycle code.

3. The method defined in claim 1 further comprising the step of:

overwriting a busy control field of a first packet on said forward path with a signal for indicating that a station has written a second packet on said forward path.

4. The method defined in claim 2 further comprising the steps of:

reading a busy control field of a first packet on said forward path; and

responsive to said read busy control field indicating that said forward path is not busy and responsive to said station having a second packet of said first traffic type to transmit, writing said second packet on said forward path, said second written packet thereby overwriting any packet on said forward path.

5. The method defined in claim 2 further comprising the steps of:

reading a busy control field of a first packet on said forward path; and

responsive to said read busy control field indicating that said forward path is busy, entering a HOLD state until another read busy control field indicates that said forward path is not busy.

6. The method defined in claim 2 further comprising the steps of:

reading a busy control field of a first packet on said forward path; and

responsive to said read busy control field indicating that said forward path is not busy, writing an end cycle code in a packet on a reverse one of said paths.

7. The method defined in claim 6 further comprising the steps of:

reading said end cycle code packet on said reverse path and

responsive to said read end cycle code, writing a second start cycle code in a packet on said forward path, said second start cycle code being written by said head station and said second start cycle code including a start cycle field responsive to which a station on said forward path and down the line from said head station relative to said forward path may be initialized to transmit a second type of traffic packet.

8. The method defined in claim 2 further comprising the step of:

responsive to said first read start cycle code, writing an end cycle code in a packet on a reverse one of said paths.

9. A communications system including a plurality of stations, at least two of said stations being coupled to first and second separate independent, unidirectional and oppositely directed signal paths, means for writing signals on either of said paths and means for reading signals from either of said paths and characterized in that said system further comprising:

means for writing a first start cycle code in a predetermined field of a packet on a forward one of said paths, said first start cycle code being written by a head station and said first start cycle code for identifying a first type of traffic which may be written by a station down the line from said head station relative to said forward path in a packet on said forward path.

10. The system defined in claim 9 further comprising:

means for reading said first start cycle code by a first station down the line from said head station relative to said forward path on said forward path; and

means, responsive to said first read start cycle code, for initializing said first station for writing said first type of traffic identified by said start cycle code.

11. The system defined in claim 9 further comprising

means for overwriting a busy control field of a first packet on said forward path with a signal for indicating that a station has written a second packet on said forward path.

12. The system defined in claim 10 further comprising:

means for reading a busy control field of a first packet on said forward path; and

means, responsive to said read busy control field indicating that said forward path is not busy and responsive to said station having a second packet of said first type to transmit, for writing said second packet on said forward path, said second written packet thereby overwriting any packet on said forward path.

13. The system defined in claim 10 further comprising:

means for reading a busy control field of a first packet on said forward path; and

means, responsive to said read busy control field indicating that said forward path is busy, for entering a HOLD state until another read busy control field indicates that said forward path is not busy.

14. The system defined in claim 10 further comprising:

means for reading a busy control field of a first packet on said forward path; and

means, responsive to said read busy control field indicating that said forward path is not busy, for writing an end cycle code in a packet on a reverse one of said paths.

15. The system defined in claim 14 further comprising:

means for reading said end cycle code packet on said reverse path and

means, responsive to said read end cycle code, for writing a second start cycle code in a packet on said forward path, said second start cycle code being written by said head station and said second start cycle code including a start cycle field responsive to which a station on said forward path may be initialized to transmit a second type of traffic packet.

16. The system defined in claim 10 further comprising:

means, responsive to said first start cycle code, for writing an end cycle code in a packet on a reverse one of said paths.

17. Station apparatus for controlling digital signals in a communication system, said station adapted to be coupled to first and second separate, independent, unidirectional and oppositely directed signal paths, said station including means for writing signals on either of said paths and means for reading signals from either of said paths and characterized in that said station further comprises:

means for writing a first start cycle code in a predetermined field of a packet on a forward one of said paths, said first start cycle code being written by a head station and said first start cycle code for identifying a first type of traffic which may be written by a station along said forward path and down the line from said head station relative to said forward path in a packet on said forward path.

18. The station defined in claim 17 further comprising:

means for reading said first start cycle code on said forward path; and

means, responsive to said first read start cycle code, initializing said station for writing said type of traffic identified by said start cycle code.

19. The station defined in claim 17 further comprising:

means for overwriting a busy control field of a first packet on said forward path with a signal for indicating that said station has written a second packet on said forward path.

20. The station defined in claim 18 further comprising:

means for reading a busy control field of a first packet on said forward path; and

means, responsive to said read busy control field indicating that said forward path is not busy and responsive to said station having a second packet of said first traffic type to transmit, for writing said second packet on said forward path, said second written packet thereby overwriting any packet on said forward path.

21. The station defined in claim 18 further comprising:

means for reading a busy control field of a first packet on said forward path; and

means, responsive to said read busy control field indicating that said forward path is busy, for entering a HOLD state until another read busy control field indicates that said forward path is not busy.

22. The station defined in claim 18 further comprising:

means for reading a busy control field of a first packet on said forward path; and

means, responsive to said read busy control field indicating that said forward path is not busy, for writing an end cycle code in a packet on a reverse one of said paths, said end cycle code being written by a last station on said forward path.

23. The station defined in claim 22 further comprising:

head station means for reading said end cycle code packet on said reverse path,

head station means, responsive to said read end cycle code, for writing a second start cycle code in a packet on said forward path, said second start cycle code being written by said head station and said second start cycle code including a start cycle field responsive to which a station on said forward path may be initialized to transmit a second type of traffic packet.

24. The station defined in claim 18 further comprising:

means, responsive to said first read start cycle code, for writing an end cycle code in a packet on a reverse one of said paths, said end cycle code being written by a last station on said forward path.