Network protocol for integrating synchronous and asynchronous traffic on a common serial data bus

• US 4,593,282 A
• Filed: 04/14/1983
• Issued: 06/03/1986
• Est. Priority Date: 04/14/1983
• Status: Expired due to Term

• Current Assignee: American Bell Incorporated
• Original Assignee: AT&T Information Systems Inc. (AT&T, Inc.)
• Inventors: Tsao, Chan D., Hluchjy, Michael G., Acampora, Anthony
• Primary Examiner(s): Yusko, Donald J.
• Assistant Examiner(s): Hodgkins, Sharon L.
• Application Number:
  US06/485,034
• Time in Patent Office: 1,146 Days
• Field of Search: 340/825.05, 340/825.07, 340/825.14, 340/825.5, 340/825.51, 370/60, 370/94, 370/79, 370/85, 370/86, 370/89, 370/91, 370/95
• US Class Current: 370/447
• CPC Class Codes: H04L 12/4135 using bit-wise arbitration
• CPC Class Codes: H04L 12/64 Hybrid switching systems

Abstract

Contention among a plurality of synchronous and asynchronous devices connected to a shared communication medium for access to time slots in a sequence of frames is resolved by assigning a unique priority word including a priority code prefix to each device and granting access to a given slot by comparing the values of the priority words assigned to competing devices. The priority code prefix is assigned as a joint function of whether synchronous or asynchronous communication is desired and whether synchronous communication is being initiated or continued. In each assignment protocol, synchronous communication is enabled by assuring any device that initially gains access to a particular time slot continued access to the same slot in succeeding frames. If desired, devices with synchronous access may relinquish unused time slots to asynchronous traffic, while reserving the ability to resume synchronous communication.

Claims

1. A technique for enabling a plurality of devices of initial and ongoing synchronous and asynchronous communication to gain access to time slots on a shared communication medium, each of said time slots occurring at a preselected frame rate, comprising:

assigning priority information to each device, representing a priority level associated with that device, said priority information including variable information,

granting access to a time slot by evaluating said priority information assigned to devices contending for that slot,

wherein said assigning step is CHARACTERIZED BY

forming said variable information as a function of (a) the synchronous or asynchronous nature of the communication desired by the device, and (b) the initial or ongoing status of said synchronous communication, wherein

a higher one of said priority levels is assigned to ongoing synchronous communication and a lower one of said priority levels is assigned to initial synchronous communication, both as compared to the one of said priority levels assigned to asynchronous communication.

2. The technique defined in claim 1 CHARACTERIZED IN THAT said priority information assigning step includes prefixing a unique binary number associated with each of said devices with said variable information, and

said access granting step includes evaluating said priority information on a bit by bit basis, most significant bit first.

3. The technique defined in claim 2 CHARACTERIZED IN THAT said variable information includes a two bit code assigned according to the following table:

space="preserve" listing-type="tabular">______________________________________ Code ______________________________________ Ongoing Synchronous Communication 11 Initial Synchronous Communication 00 Asynchronous Communication 10 ______________________________________

4. The technique defined in claim 3 wherein said assigning step is FURTHER CHARACTERIZED BY assigning a code "01" during selected time slots accessed by one of said devices engaged in ongoing synchronous communication, whereby said selected time slots may be relinquished to another of said devices for asynchronous communication.

5. The invention defined in claim 3 CHARACTERIZED IN THAT ones of said devices engage in ongoing synchronous communication at a rate less than said frame rate, said variable information further includes a b-bit prefix indicating said lesser rate, and said access granting step further includes comparing said b-bit prefix for a device having synchronous access with said b-bit prefix for devices seeking synchronous access.

6. A method of resolving contention among a plurality of devices connected to a shared communication medium for access to time slots in a sequence of frames including the steps of:

assigning a unique priority word to each device contending for access to any time slot, and

granting access to a time slot to one of said contending devices by comparing the values of said priority words assigned to each of said contending devices,

CHARACTERIZED IN THAT said priority word assigning steps includes;

(1) assigning a low value priority word to a device initially contending for access to said medium for synchronous communication, and

(2) assigning a high value priority word to a device seeking synchronous communication which has already gained access to a particular time slot, said high value priority word assuring said device access to said medium during subsequent occurrences of said time slot in succeeding frames.

7. The method defined in claim 6 wherein said priority word includes a fixed portion uniquely identifying each of said devices and a priority code prefix.

8. The method defined in claim 7 wherein said assigning step includes selecting said priority code as a "0" for said low value and as a "1" for said high value.

9. The method defined in claim 7 wherein said assigning step further includes selecting said priority code as "00" for said low value and as "11" for said high value.

10. The method defined in claim 9 wherein at least one of said devices contending for access to said medium for asynchronous communication is assigned a priority code of "10" between said high value and said low value.

11. The method defined in claim 10 wherein said assigning step further includes selecting said priority code as "01" during time slots relinquished by devices engaged in ongoing synchronous communication for use in asynchronous communication.

12. The method defined in claim 7 wherein said access granting step includes:

comparing the values of said priority words on a bit by bit basis, most significant bit first, and

selectively suppressing the comparison of at least one of the bits of said priority words.

13. The method defined in claim 12 wherein said suppression is selected as a function of the synchronous or asynchronous nature of the communication desired by said devices.

14. A technique for enabling one of a plurality of devices contending for access to time slots on a shared communication medium to gain access to said medium for asynchronous or synchronous communication, synchronous communication requiring access to at least one particular time slot in each of a sequence of frames each of which includes an integral number of time slots, including the steps of:

assigning a uniquely valved priority word to each device contending for access to one of said time slots, and

granting access to a time slot to one of said contending devices by comparing, most significant bit first, the values of said assigned priority words,

CHARACTERIZED IN THAT said priority word assigning step includes;

selecting said priority word as a joint function of

(1) whether a device is contending for synchronous or asynchronous access, and

(2) whether a device contending for synchronous access is initially contending for a time slot or has already accessed a particular time slot.

15. The technique defined in claim 14 wherein said assigning step is further characterized by

forming said priority word by prefixing a binary number uniquely identifying each of said devices with a priority code containing at least one bit.

16. The technique defined in claim 15 wherein said assigning step includes selecting a one bit priority code according to the following table:

space="preserve" listing-type="tabular">______________________________________ Contention For;

Priority Code ______________________________________ Asynchronous or initial 0 synchronous access Continued synchronous access 1 ______________________________________

17. The technique defined in claim 15 wherein said assigning step includes forming a three bit priority code according to the following table:

space="preserve" listing-type="tabular">______________________________________ Contention For;

Priority Code ______________________________________ Continued synchronous access 111 Asynchronous access 110 to 010 Initial synchronous access 000 ______________________________________

18. The technique defined in claim 14 wherein said assigning step includes forming a two bit priority code according to the following table:

space="preserve" listing-type="tabular">______________________________________ Contention For;

Priority Code ______________________________________ Continued synchronous access 11 Asynchronous Access 10 Initial synchronous access 00 ______________________________________

19. The technique defined in claim 18 wherein said assigning step includes changing said priority code from 11 to 01 when a device which already has access to a particular time slot relinguishes said slot to another device seeking asynchronous access.

20. An apparatus for enabling a plurality of devices capable of initial and ongoing synchronous and asynchronous communication to gain access to time slots on a shared communication medium, each of said time slots occurring at a preselected frame rate, comprising:

means for assigning priority information to each device, said information including variable information,

means for granting access to a time slot by evaluating the priority information assigned to devices contending for that slot,

characterized in that said assigning means includes means for forming said variable information as a function of (a) the synchronous or asynchronous nature of the communication desired by the device, and (b) the initial or ongoing status of said synchronous communication, and

for assigning higher priority to ongoing synchronous communication and lower priority to initial synchronous communication, both as compared to the priority assigned to asynchronous communication.

21. The apparatus defined in claim 20 characterized in that said priority assigning means is arranged to prefix a unique binary number associated with each of said devices with said variable information, and

said access granting means is arranged to evaluate said priority information on a bit by bit basis, most significant bit first.

22. The apparatus defined in claim 21 characterized in that said variable information formed in said priority assigning means includes a two bit code assigned according to the following relationship:

space="preserve" listing-type="tabular">______________________________________ Code ______________________________________ Ongoing Synchronous Communication 11 Initial Synchronous Communication 00 Asynchronous Communication 10 ______________________________________

23. The apparatus defined in claim 22 further characterized in that said assigning means is arranged to assign a code "01" during selected time slots accessed by one of said devices engaged in ongoing synchronous communication, whereby said selected time slots may be relinquished to another of said devices for asynchronous communication.

24. The invention defined in claim 20 characterized in that ones of said devices engage in ongoing synchronous communication at a rate less than said frame rate, said variable information further includes a b-bit prefix indicating said lesser rate, and said access granting means is further arranged to compare said b-bit prefix for a device having synchronous access with said b-bit prefix for devices seeking synchronous access.

27. The invention defined in claim 21 wherein said assigning means is arranged to select said priority code as a "0" for said low value and as a "1" for said high value.

25. Apparatus for resolving contention among a plurality of devices connected to a shared communication medium for access to time slots in a sequence of frames including:

means for assigning a uniquely valued priority word to each device contending for access to any time slot, and

means for granting access to a time slot to one of said contending devices by comparing the values of said priority words assigned to each of said contending devices,

characterized in that said priority word assigning means is arranged to;

(1) assign a low value priority word to a device initially contending for access to said medium for synchronous communication, and

(2) assign a high value priority word to a device seeking synchronous communication which has already gained access to a particular time slot, said high value priority word assuring said device access to said medium during subsequent occurrences of said time slot in succeeding frames.

26. The invention defined in claim 25 wherein said priority word includes a fixed portion uniquely identifying each of said devices and a priority code prefix.

28. The invention defined in claim 26 wherein said assigning means is arranged to select said priority code as "00" for said low value and as "11" for said high value, and select said priority code as 10 for devices seeking asynchronous communication.

29. The invention defined in claim 28 wherein said assigning means is further arranged to select said priority code as 01 during time slots relinquished by devices engaged in ongoing synchronous communication for use in asynchronous communication.

30. Apparatus for enabling one of a plurality of devices contending for access to time slots on a shared communication medium to gain access to said medium for asynchronous or synchronous communication, synchronous communication requiring access to at least one particular time slot in each of a sequence of frames each of which include an integral number of time slots, including:

means for assigning a uniquely valued priority word to each device contending for access to one of said time slots, and

means for granting access to a time slot to one of said contending devices by comparing, most significant bit first, the values of said assigned priority words,

characterized in that said priority word assigning means is arranged to;

select said priority word as a joint function of

(1) whether a device is contending for synchronous or asynchronous access, and

(2) whether a device contending for synchronous access is initially contending for a time slot or has already accessed a particular time slot.

31. The apparatus defined in claim 30 wherein said assigning means is arranged to

form said priority word by prefixing a binary number uniquely identifying each of said devices with a priority code containing at least one bit.

32. The apparatus defined in claim 31 wherein said assigning means is arranged to form a one bit priority code according to the following table:

space="preserve" listing-type="tabular">______________________________________ Contention For;

Priority Code ______________________________________ Asynchronous or initial 0 synchronous access Continued synchronous access 1 ______________________________________

33. The apparatus defined in claim 31 wherein said assigning means is arranged to form a two bit priority code according to the following table:

space="preserve" listing-type="tabular">______________________________________ Contention For;

Priority Code ______________________________________ Continued synchronous access 11 Asynchronous Access 10 Initial synchronous access 00 ______________________________________

34. The apparatus defined in claim 33 wherein said assigning means is arranged to change said priority code from 11 to 01 when a device which already access a particular time slot relinquishes said slot to another device seeking asynchronous access.

35. The apparatus defined in claim 31 wherein said assigning means is arranged to form a three bit priority code according to the following table:

space="preserve" listing-type="tabular">______________________________________ Contention For;

Priority Code ______________________________________ Continued synchronous access 111 Asynchronous access 110 to 010 Initial synchronous access 000 ______________________________________