Method and apparatus for interconnection of flow-controlled communication

• US 6,798,744 B1
• Filed: 05/19/2000
• Issued: 09/28/2004
• Est. Priority Date: 05/14/1999
• Status: Expired due to Fees

• Current Assignee: PMC-Sierra Incorporated (Microchip Technology Incorporated)
• Original Assignee: PMC-Sierra Incorporated (Microchip Technology Incorporated)
• Inventors: Brown, Jeffery John, Bradshaw, John Richard, Loewen, Jonathan David
• Primary Examiner(s): Hsu, Alpus H.
• Assistant Examiner(s): Nguyen, Toan D.
• Application Number:
  US09/574,305
• Time in Patent Office: 1,593 Days
• Field of Search: 370/395.21, 370/395.4, 370/395.41, 370/442-462, 370/230, 370/231, 370/235, 370/236
• US Class Current: 370/235
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04L 47/2441 relying on flow classification, e.g. using integrated services [IntServ]
• CPC Class Codes: H04L 47/266 Stopping or restarting the source, e.g. X-on or X-off
• CPC Class Codes: H04L 47/283 in response to processing delays, e.g. caused by jitter or round trip time [RTT]
• CPC Class Codes: H04L 47/50 Queue scheduling
• CPC Class Codes: H04L 47/6255 queue load conditions, e.g. longest queue first
• CPC Class Codes: H04L 69/14 Multichannel or multilink protocols
• CPC Class Codes: H04L 69/22 Parsing or analysis of headers

Abstract

A method or system or apparatus provides improved digital communication. In one aspect, flow control in performed by receiving status preprended to data units in a combined data channel, where the status data indicated the available status of a number of far end receiving channels. Thus data may be sent only to available receiving channels. In a further aspect, a frequency reference may also be transmitted by including data in data units in a combined channel. In a further aspect, an active channel can be selected among two redundant channels by use of an active bit in said data units. The invention has particular applications to ATM-type communication systems and may also be used in other communication systems.

Claims

1. A method of flow control in a digital communications system wherein data flows in a first direction in a channel and in a second opposite direction in multiple channels comprising:

in a transferred data unit in said first direction, including a portion of data indicating available/not-available status of a set of channels in said second direction;

prior to selecting a channel in said second direction for transmitting a data unit, checking status of said channel as indicated in said portion;

selecting a channel for transmission from among channels indicated available in said portion; and

wherein said portion indicates status of a part of possible channels in said second direction and wherein multiple data units in said first direction must be received to update status of all channels in said second direction.

2. The method according to claim 1 wherein there is a delay between reception of said portion and said selecting and wherein sufficient buffering is provided on said second channels to compensate for said delay.

3. The method according to claim 1 wherein said portion comprises a set of bit-flags, the state of each bit flag indicating available/not-available status of one of said channels in said second direction.

4. The method according to claim 1 wherein said status indicates space available in a buffer for a second direction channel and wherein a number of spare buffer locations are available to compensate for a delay in signaling said status.

5. The method according to claim 1 wherein a cell transmitted on a link includes a bit-oriented code (BOC) portion, wherein BOCs are used to carry predefined or user-defined signaling.

6. The method according to claim 5 wherein bit oriented codes are transmitted as a repeating 16-bit sequence consisting of 8 ones, a zero, 6 code bits, and a trailing zero.

7. The method according to claim 1 wherein:

said flow control is per logical channel;

said portion comprises multiple bits per data unit used to indicate downstream status; and

wherein said per logical channel flow control uses a simple XON/XOFF control.

8. The method according to claim 1 further comprising:

including in said data units a timing reference independent of a serial link bit rate.

9. The method according to claim 1 wherein each data unit transmitted contains downstream status information.

10. The method according to claim 9 wherein each data unit transmitted in said first direction contains 16 bits of information that convey the status for 16 of 32 active channels in said second direction.

11. The method according to claim 1 wherein a separate overhead bit per data unit conveys buffer status of a far-end microprocessor port.

12. A method for downstream data flow control comprising:

placing cells for downstream channels into a plurality of buffers, said buffers grouped into sets of buffers;

for a set of said sets, scheduling a cell out of said set and transmitting said cell to an access module, said access module serving a plurality of channels;

said scheduling comprising;

eliminating from a scheduling round a channel that is presenting a far-end buffer full status;

performing an access algorithm among remaining eligible channels to share a downstream link; and

when there is no data in any buffer in a set of buffers, generating a stuff cell for said set and transmitting said stuff cell on a link for said set.

13. The method according to claim 12 wherein said plurality of buffers comprises at least a single cell buffer for each channel and wherein said sets are each assigned to a link, said link providing a serial data connection from a scheduler to an access module.

14. The method according to claim 12 wherein scheduling of a cell is performed when a previous cell has been fully transmitted from a buffer over a link.

15. A method for upstream data flow control comprising:

placing cells for upstream transmission from a plurality of logical channels into a plurality of shared buffers; and

servicing said shared buffers with a weighted round-robin algorithm to present said cells to an upstream bus master as a single cell stream wherein when an upstream buffer has less than a preset number of empty cell buffers, said upstream buffer deasserts a cell available bit sent in system overhead of a corresponding downstream link and wherein a far end device begins sending stuff cells upon indication that the upstream buffer is unavailable.

16. The method according to claim 15 wherein said present number is three, allowing for two additional cells to be accepted after a cell available bit is deasserted.

17. A digital communications system wherein data flows in a first direction in a channel and in a second opposite direction in multiple channels comprising:

means for performing flow control comprising;

means for including a portion of data indicating available/not-available status of a set of channels in said second direction in a transferred data unit in said first direction;

means for checking status of said channel as indicated in said portion prior to selecting a channel in said second direction for transmitting a data unit;

means for selecting a channel for transmission from among channels indicated available in said portion; and

wherein said portion indicates status of a part of possible channels in said second direction and wherein multiple data units in said first direction must be received to update status of all channels in said second direction.

18. The system of claim 17 wherein there is a delay between reception of said portion and said selecting and further comprising means for sufficient buffering on said second channels to compensate for said delay.

19. The system of claim 17 wherein said portion comprises flag means, the state of each flag means indicating available/not-available status of one of said channels in said second direction.

20. The system of claim 17 wherein:

said status indicates space available in a buffer for a second direction channel and wherein a number of spare buffer locations are available to compensate for a delay in signaling said status.

21. The system of claim 17 further comprising:

means for including a bit-oriented code (BOC) portion in a cell transmitted on a link, wherein BOCs are used to carry predefined or user-defined signaling;

means for performing flow control per logical channel;

means for including in said data units a timing reference independent of a serial link bit rate; and

means for including in transmitted data units downstream status information.

22. The system of claim 17 further wherein:

said portion comprises multiple bits per data unit used to indicate downstream status;

said per logical channel flow control means uses a simple XON/XOFF control;

a separate overhead bit per data unit conveys buffer status of a far-end microprocessor port.

23. A downstream data flow controller comprising:

means for placing cells for downstream channels into a plurality of buffer means, said buffer means grouped into sets of buffer means;

means for scheduling a cell out of a set of said sets;

means for transmitting said cell to an access module, said access module serving a plurality of channels;

means for eliminating from a scheduling round a channel that is presenting a far-end buffer full status; and

means for performing an access algorithm among remaining eligible channels to share a downstream link,

means for generating a stuff cell for said set and means for transmitting said stuff cell on a link for said set when there is no data in any buffer means in a set.

24. An upstream data flow controller comprising:

means for placing cells for upstream transmission from a plurality of logical channels into a plurality of shared buffer means; and

means for servicing said shared buffer means with a weighted round-robin algorithm to present said cells to an upstream bus master means as a single cell stream;

wherein when an upstream buffer means has less than a preset number of empty cell buffers, said upstream buffer means deasserts a cell available bit sent in system overhead of a corresponding downstream link and wherein a far end device begins sending stuff cells upon indication that the upstream buffer means is unavailable.