Method for communicating backpressure messages in a data communications system
A method for communicating backpressure messaging over a serial encoded link is disclosed. Embodiments of the invention enable advanced backpressure signaling to be retrofitted into legacy systems to achieve performance improvements and support new or enhanced services. Specifically, such signaling enables per-context and per-priority backpressure signaling information to be conveyed by a backpressure message; thereby enabling flow control to be performed in accordance with a priority or context associated with a traffic flow, or flows, carried over the serial link.
1. A method of communicating an in-band backpressure signaling message (IBSM) over a first serial encoded link, the method comprising:
receiving, by a receiver of packets over a first serial encoded link, at least one protocol data unit (PDU) from a first data transmitter;
forming, by the receiver of packets over the first serial encoded link, a backpressure message PDU when triggered by a contextual control scheme, the step comprising:
forming a start of backpressure delineator (SBP), wherein the SBP includes a control character and a data character representing a backpressure message packet (BP) length between 2 and 128 bytes;
appending, to the SBP, the BP that supports backpressure signaling operations, comprising a plurality of 2-byte data blocks, each 2-byte data block including a first plurality of bits corresponding to the contextual control scheme and a second plurality of bits comprising a BP context for the contextual control scheme, wherein the BP context is one of a plurality of contexts supported by the contextual control scheme;
transmitting, by the receiver of packets, the backpressure message PDU on the first serial encoded link to the first data transmitter, wherein the first data transmitter uses a first BP context of a first 2-byte data block to modify the first serial encoded link; and
transmitting, by the first data transmitter, the backpressure message to a second data transmitter over a second serial encoded link, wherein the second data transmitter sends at least one PDU to the first data transmitter, the first serial encoded link includes fewer contexts than the plurality of BP contexts fully encoded in the backpressure message, and the second data transmitter uses at least one BP context of the plurality of BP contexts to modify the second serial encoded link.
2. The method of claim 1 , wherein the backpressure message PDU replaces an idle link PDU that occupies idle time on the first serial encoded link, and further wherein the backpressure message PDU supports a backpressure signaling operation and a timing operation.
3. The method of claim 2 , wherein the length of the backpressure message PDU is equal to the length of the replaced idle link PDU.
4. A method of communicating an in-band backpressure signaling message (IBSM) over a first 8B10B serial encoded link, the method comprising:
receiving, by a receiver of packets over the first 8B10B serial encoded link, at least one protocol data unit (PDU) from a first data transmitter;
forming, by the receiver of packets over the first 8B10B serial encoded link, a backpressure message PDU when triggered by a contextual control scheme, the step comprising:
forming a start of backpressure delineator (SBP), wherein the SBP includes an 8B10B control character and a data character representing a backpressure message packet (BP) length between 2 and 128 bytes;
appending, to the SBP, the BP that supports backpressure signaling operations, comprising a plurality of 2-byte data blocks, each 2-byte data block including a first plurality of bits corresponding to the contextual control scheme and a second plurality of bits comprising a BP context for the contextual control scheme, wherein the BP context is one of a plurality of contexts supported by the contextual control scheme;
transmitting, by the receiver of packets, the backpressure message PDU on the first 8B10B serial encoded link to the first data transmitter, wherein the first data transmitter uses a first BP context of a first 2-byte data block to modify the first 8B10B serial encoded link; and
transmitting, by the first data transmitter, the backpressure message to a second data transmitter over a second serial encoded link, wherein the second data transmitter sends at least one PDU to the first data transmitter, the first serial encoded link includes fewer contexts than the plurality of BP contexts fully encoded in the backpressure message, and the second data transmitter uses at least one BP context of the plurality of BP contexts to modify the second serial encoded link.
5. The method of claim 1 , wherein the number of contexts included in the backpressure message determines the length of the BP.
6. The method of claim 5 , wherein the BP contains a 2-byte contextual data block for each BP context, wherein the BP includes a maximum of 64 2-byte contextual data blocks.
7. The method of claim 1 , wherein each of the plurality of BP contexts enables each data transmitter to independently modify one of a plurality of serial encoded links.
8. The method of claim 4 , wherein the control character in the SBP is one from the group of K28.0, K28.4, K28.6.
9. A system of communicating an in-band backpressure signaling message (IBSM) over a serial encoded link, the method comprising:
a first serial encoded link that sends packets from a first data transmitter to a receiving device;
the receiving device that forms a backpressure message protocol data unit (PDU) when triggered by a contextual control scheme and transmits the backpressure message PDU on the first serial encoded link to the first data transmitter, wherein:
the formation of the backpressure message PDU comprises forming a start of backpressure delineator (SBP), wherein the SBP includes a control character and a data character representing a backpressure message packet (BP) length between 2 and 128 bytes and appending, to the SBP, the BP that supports backpressure signaling operations comprising a plurality of 2-byte data blocks, each 2-byte data block including a first plurality of bits corresponding to the contextual control scheme and a second plurality of bits comprising a BP context for the contextual control scheme, wherein the BP context is one of a plurality of contexts supported by the contextual control scheme;
the first data transmitter that:
sends at least one PDU to the receiving device,
receives the backpressure message PDU on the first serial encoded link from the receiving device, and
uses a first BP context of a first 2-byte data block to modify the first serial encoded link; and
a second serial encoded link that sends packets from a second data transmitter to the first data transmitter, wherein the first serial encoded link includes fewer contexts than the plurality of BP contexts fully encoded in the backpressure message; and
the second data transmitter that sends packets to the first data transmitter and receives the backpressure message PDU on the second serial encoded link from the first data transmitter, wherein the second data transmitter uses at least one BP context of the plurality of BP contexts to modify the second serial encoded link.
10. The system of claim 9 , wherein each of the plurality of BP contexts enables each data transmitter to independently modify one of a plurality of serial encoded links.
11. The system of claim 9 , wherein the number of contexts included in the backpressure message determines the length of the BP.
12. The system of claim 11 , wherein the BP contains a 2-byte contextual data block for each BP context, wherein the BP includes a maximum of 64 2-byte contextual data blocks.