Mechanism for providing octet alignment in serial ATM data stream

• US 7,103,049 B2
• Filed: 01/02/2002
• Issued: 09/05/2006
• Est. Priority Date: 01/02/2002
• Status: Active Grant

• Current Assignee: ADTRAN Incorporated (ADTRAN Holdings, Inc.)
• Original Assignee: ADTRAN Incorporated (ADTRAN Holdings, Inc.)
• Inventors: Otto, Christopher A., Wright, Jonathan Aaron
• Primary Examiner(s): Ngo, Ricky Q.
• Assistant Examiner(s): Liou, Jonathan
• Application Number:
  US10/040,153
• Publication Number:
  US 20030123450A1
• Time in Patent Office: 1,707 Days
• Field of Search: 370/395.1, 370/395.21, 370/395.51, 370/395.3, 370/395.5, 370/395.6, 370/476, 370507-510, 370/514
• US Class Current: 370/395.1
• CPC Class Codes: H04J 3/0632 Synchronisation of packets and cells, e.g. transmission of voice via a packet network, circuit emulation service [CES] queuing arrangements in packet switching elements H04L49/90; synchronising systems for the synchronous transmission of a pulse code modulated video signal with one or more other pulse code modulated signals H04N7/56
• CPC Class Codes: H04L 2012/5674 Synchronisation, timing recovery or alignment
• CPC Class Codes: H04L 69/324 in the data link layer [OSI layer 2], e.g. HDLC
• CPC Class Codes: H04M 11/062 using different frequency bands for speech and other data

Abstract

A byte boundary information recovery mechanism locates the first bits of respective bytes of an asynchronous transfer mode (ATM)-based serial data stream, used by a frame synchronization mechanism to delineate respective cells of the ATM stream, and thereby enables transceiver equipment to successfully receive and parse ATM traffic. The invention employs a counter offset-based scheme that generates an output signal in potential alignment with the (first bit) boundary of a byte of the data stream, in response to the contents of a counter reaching a prescribed count value. It then iteratively shifts, as necessary, the bit time at which the output signal is produced relative to the counting operation of the counter, until the output signal is aligned with the boundary of a byte of the data stream.

Claims

1. For use with a receiver of a digital communication system, said receiver having a cell delineation mechanism that is operative, given knowledge of boundaries of respective bytes of an incoming serial data stream, to delineate respective cells of said serial data stream, a mechanism for locating said boundaries of respective bytes of said incoming serial data stream comprising:

a counter that is operative to count respective clock signals associated with said incoming serial data stream; and

a synchronization signal derivation unit, coupled to said counter and being operative to generate an output signal in potential alignment with the boundary of a byte of said incoming serial data stream, in response to contents of said counter reaching a prescribed count value, and iteratively shifting, the time at which said output signal is produced relative to the counting operation of said counter, until said output signal is aligned with said boundary of a byte of said incoming serial data stream.

2. The mechanism according to claim 1, wherein said counter is operative to repetitively count toward said prescribed count value from a first preloaded count value, and wherein said synchronization signal derivation unit is operative to controllably program said counter with a second preloaded count value, different from said first preloaded count value, based upon whether or not said output signal is aligned with said boundary of a byte of said incoming serial data stream.

3. The mechanism according to claim 2, wherein said synchronization signal derivation unit is operative to iteratively program said counter with said second count value for an individual one or more count cycles, separated from one another by plural count cycles during which said counter is programmed to count from said first preloaded count value, until said output signal is aligned with said boundary of a byte of said incoming serial data stream.

4. The mechanism according to claim 1, wherein said counter is operative to generate an intermediate frame sync signal FS0 in response to contents thereof reaching a prescribed count value, and wherein said synchronization signal derivation unit includes a shift register to which said intermediate frame sync signal FS0 is serially shifted, and wherein said output signal is derived from a selected stage of said shift register.

5. The mechanism according to claim 4, wherein said synchronization signal derivation unit is operative to controllably change the stage of said shift register from which said output signal is derived in a manner that causes said output signal to be aligned with said boundary of a byte of said incoming serial data stream.

6. The mechanism according to claim 5, wherein said synchronization signal derivation unit is operative to iteratively and successively change the stage of said shift register from which said output signal is derived over successive intervals, until said output signal is aligned with said boundary of a byte of said incoming serial data stream.

7. A method for locating boundaries of respective bytes of an incoming serial data stream coupled to a receiver of a digital communication system, said receiver having a cell delineation mechanism that is operative, given knowledge of said boundaries of said respective bytes of said incoming serial data stream, to delineate respective cells of said serial data stream, said method comprising the steps of:

(a) counting respective clock signals associated with said incoming serial data stream;

(b) in response to the number of clock signals counted in step (a) reaching a prescribed count value, generating an output signal in potential alignment with the boundary of a byte of said incoming serial data stream; and

(c) iteratively adjusting the time at which said output signal is produced in step (b) relative to the counting operation carried out in step (a), until said output signal is aligned with said boundary of a byte of said incoming serial data stream.

8. The method according to claim 7, wherein step (a) comprises repetitively counting toward said prescribed count value from a first count value, and wherein step (c) comprises controllably changing said first count value to a second count value, based upon whether or not said output signal is aligned with said boundary of a byte of said incoming serial data stream.

9. The method according to claim 8, wherein step (c) comprises iteratively causing step (a) to start counting from said second count value for an individual one or more count cycles, separated from one another by plural count cycles during which step (a) counts from said first count value, until said output signal is aligned with said boundary of a byte of said incoming serial data stream.

10. The method according to claim 7, wherein step (a) comprises generating an intermediate frame sync signal FS0 in response to counting prescribed number of clock signals, said intermediate frame sync signal FS0 being shifted through a multi-stage shift register, step (b) comprises deriving said output signal from a selected stage of said shift register, and wherein step (c) comprises controllably changing the stage of said shift register from which said output signal is derived in a manner that causes said output signal to be aligned with said boundary of a byte of said incoming serial data stream.

11. The method according to claim 10, wherein step (c) comprises iteratively and successively changing the stage of said shift register from which said output signal is derived over successive intervals, until said output signal is aligned with said boundary of a byte of said incoming serial data stream.

12. A method of identifying initial bits within respective bytes of an incoming asynchronous transfer mode (ATM) data stream that is coupled to a receiver of a digital communication system, said receiver having a cell delineation mechanism that is operative, given knowledge of the locations of said initial bits, to delineate respective cells of said ATM data stream, said method comprising the steps of:

(a) counting respective clock signals associated with respective bits of said incoming ATM data stream;

(b) in response to the number of clock signals counted in step (a) reaching a prescribed count value, generating an output signal in potential alignment with a first bit of a byte of said incoming ATM data stream; and

(c) iteratively shifting in a bit-wise manner, the bit time at which said output signal is produced in step (b) relative to the counting operation carried out in step (a), until said output signal is aligned with a first bit of a byte of said incoming ATM data stream.

13. The method according to claim 12, wherein step (a) comprises repetitively counting toward said prescribed count value from a first count value, and wherein step (c) comprises controllably changing said first count value to a second count value, based upon whether or not said output signal is aligned with said first bit of a byte of said incoming ATM data stream.

14. The method according to claim 13, wherein step (c) comprises iteratively causing step (a) to start counting from said second count value for an individual one or more count cycles, separated from one another by plural count cycles during which step (a) counts from said first count value, until said output signal is aligned with said first bit of a byte of said incoming ATM data stream.

15. The method according to claim 14, wherein step (a) comprises generating an intermediate frame sync signal FS0 in response to counting prescribed number of clock signals, said intermediate frame sync signal FS0 being shifted through a multi-stage shift register, step (b) comprises deriving said output signal from a selected stage of said shift register, and wherein step (a) comprises controllably changing the stage of said shift register from which said output signal is derived in a manner that causes said output signal to be aligned with said first bit of a byte of said incoming ATM data stream.

16. The method according to claim 15, wherein step (c) comprises iteratively and successively changing the stage of said shift register from which said output signal is derived over successive intervals, until said output signal is aligned with said first bit of a byte of said incoming ATM data stream.