Motivation There are cases when TCP cannot use fast retransmit to recover from loss which requires the use of the often costly RTO Eg consider a TCP connection with a cwnd of 3 packets 1 ID: 416960
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Early Retransmit for TCPdraft-allman-tcp-early-rexmt-05.txtMark Allman, Konstantin Avrachenkov, Urtzi Ayesta, Josh BlantonTCPM - IETF 69 Motivation There are cases when TCP cannot use fast retransmit to recover from loss which requires the use of the (often costly) RTO. E.g., consider a TCP connection with a cwnd of 3 packets, 1 of which gets dropped and nothing new to send there is no chance of getting 3 duplicate ACKs TCPM-69 2 Motivation (cont.) Limited Transmit (RFC 3042) helps if we can send new data But, sometimes the app has nothing else to send And, sometimes the receiver's advertised window will not allow the sender to transmit new packets TCPM-69 3 Early Retransmit If the cwnd 4*MSS and the sender cannot send new data via Limited Transmit: trigger fast retransmit on cwnd - 1 duplicate ACKs TCPM-69 4 Costs and Benefits Benefits avoid RTOs in cases where we cannot currently trigger fast retransmit Costs less robust to reordering see "worst case" scenarios in the draft TCPM-69 5 Going Forward Should this be a WG item? we let it die; but people keep asking .... goal: experimental for people to gain experience with TCPM-69 6