Bandwidth optimization using coalesced DUP ACKs
After sending M consecutive DUP ACKs, M generally being three, the TCP receiver generates DUP ACKs every N packets, with N greater than one, with the eventually transmitted DUP ACK containing SACK information. After receiving the third DUP ACK the TCP transmitter uses the positive acknowledgements provided in the SACK information in the TCP header to inflate the congestion window. With the reduced DUP ACKs from the TCP receiver to the TCP transmitter, the impact of TCP DUP ACKs on the data rate from the TCP receiver to the TCP transmitter is substantially reduced.
1. A transmission control protocol (TCP) receiver comprising:
a port for receiving and transmitting TOP packets;
packet detection logic coupled to said port to determine, and indicate when a TCP packet has been received and has been missed based on receipt of a TCP packet; and
acknowledgement (ACK) logic coupled to said packet detection logic and said port to provide a duplicate ACK for transmission from said port for each received packet indication after an indication of a missed packet indication by said packet detection logic until M duplicate ACKs have been provided, M being a value sufficient to trigger retransmission, and then to provide a duplicate ACK for transmission from said port every N th number of received packet indications, N being greater than one, said duplicate ACKs provided every N th number of received packet indications including selective acknowledgement (SACK) information on packets received; wherein M equals 3.
2. The TCP receiver of claim 1 , wherein said M duplicate ACKs include SACK information.
3. A transmission control protocol (TOP) transmitter comprising: a port for receiving and transmitting TCF packets; a packet buffer coupled to said port for storing packets to be transmitted; ACK/SACK logic coupled to said packet buffer and said port for receiving and processing acknowledgements (ACKs) and selective acknowledgment (SACK) information received at said port, said SACK information including packets received, said ACK/SACK logic cooperating with said packet buffer to retransmit a given packet after said given packet has been indicated missing by three duplicate ACKs, only thereafter receiving duplicate ACKs with SACK information every N th number of received packets after the successful receipt of a first number of packets after said missing packet and thereafter receiving an ACK including said missing packet; and window logic coupled to said ACK/SACK logic to inflate the congestion window by the size of packets indicated received by said ACK/SACK logic and to reduce the congestion window size when said missing packet is indicated received by an ACK.
4. The TCP transmitter of claim 3 , wherein the congestion window inflation is started on the first duplicate ACK after the third duplicate ACK.
5. A network comprising: a network Internet protocol (IP) link; a transmission control protocol (TCP) receiver coupled to said IP link, said TCP receiver including: a TCP receiver port coupled to said IP link for receiving and transmitting TCP packets; packet detection logic coupled to said TCP receiver port to determine and indicate when a TCP packet has been received and has been missed based on receipt of a TCP packet; and acknowledgement (ACK) logic coupled to said packet detection logic and said TCP receiver port to provide a duplicate ACK for transmission from said TCP receiver port for each received packet indication after an indication of a missed packet indication by said packet detection logic until M duplicate ACKs have been provided. M being a value sufficient to trigger retransmission, and then to provide a duplicate ACK for transmission from said TCP receiver port every N th number of received packet indications, N being greater than one, said duplicate ACKs provided every N th number of received packet indications including selective acknowledgment (SACK) information on packets received; and a TCP transmitter coupled to said IP link, said TCP transmitter including: a TCP transmitter port coupled to said IP link for receiving and transmitting TCP packets; a packet buffer coupled to said TCP transmitter port for storing packets to be transmitted; ACK/SACK logic coupled to said packet buffer and said TCF transmitter port for receiving and processing ACKs and SACK information received at said TCP transmitter port, said ACK/SACK logic cooperating with said packet buffer to retransmit a given packet after said given packet has been indicated missing by M duplicate ACKs, only thereafter receiving duplicate ACKs with SACK information every N th number of received packets after the successful receipt of a first number of packets after said missing packet and thereafter receiving an ACK including said missing packet; and window logic coupled to said ACK/SACK logic to inflate the congestion window by the size of packets indicated received by said ACK/SACK logic and to reduce the congestion window size when said missing packet is indicated received by an ACK.
6. The network of claim 5 , wherein said M duplicate ACKs include SACK information.
7. The network of claim 5 , wherein M equals 3.
8. The network of claim 5 , wherein the congestion window inflation is started on the first duplicate ACK after the third duplicate ACK.
9. A method comprising:
receiving a sequence of transmission control protocol (TCP) packets;
determining that a TCP packet in said sequence has been missed; and
providing a duplicate acknowledgement (ACK) for transmission for each received packet indication after an indication of a missed packet indication by said packet detection logic until M duplicate ACKs have been provided, M being a value sufficient to trigger retransmission, and then providing a duplicate ACK for transmission every N th number of received packet indications, N being greater than one, said duplicate ACKs provided every N th number of received packet indications including selective acknowledgment (SACK) information on packets received; wherein M equals 3.
10. The method of claim 9 , wherein said M duplicate ACKs include SACK information.
11. A method comprising: transmitting a sequence of transmission control protocol (TCP) packets; receiving duplicate acknowledgements (ACKs) for a missing given packet; retransmitting said missing given packet after said given packet has been indicated missing by three duplicate ACKs; only after receiving three duplicate ACKs thereafter receiving duplicate ACKs with selective acknowledgment (SACK) information every N th number of received packets after the successful receipt of a first number of packets after said missing packet, said SACK information including packets received: after receiving duplicate ACKs with SACK information every N th number of received packets thereafter receiving an ACK including said missing packet; and inflating the congestion window by the size of packets received and reducing the congestion window size when said missing packet is received.
12. The method of claim 11 , wherein the congestion window inflation is started on the first duplicate ACK after the third duplicate ACK.