The Eifel Detection Algorithm for TCP

Abstract

The Eifel detection algorithm allows a TCP sender to detect a posteriori whether it has entered loss recovery unnecessarily. It requires that the TCP Timestamps option defined in RFC 1323 be enabled for a connection. The Eifel detection algorithm makes use of the fact that the TCP Timestamps option eliminates the retransmission ambiguity in TCP. Based on the timestamp of the first acceptable ACK that arrives during loss recovery, it decides whether loss recovery was entered unnecessarily. The Eifel detection algorithm provides a basis for future TCP enhancements. This includes response algorithms to back out of loss recovery by restoring a TCP sender's congestion control state. Terminology

The NewReno Modification to TCP's Fast Recovery Algorithm

“…The heuristic can also fail if a timeout was spurious and returning ACKs are not from retransmitted segments. This can be prevented by detection algorithms such as the Eifel detection algorithm [RFC3522].…”

A Throughput Analysis of TCP in ADHOC Networks

“…The scheme proposed in [5] dynamically adapts the MAC layer retry limit to reduce performance degradations due to spurious triggering of TCP congestion control. The Eifel detection algorithm [7] allows a TCP sender to detect a posteriori whether it has entered into the loss recovery phase unnecessarily. This algorithm tries to nullify the effects of spurious timeouts.…”

Using TCP Duplicate Selective Acknowledgement (DSACKs) and Stream Control Transmission Protocol (SCTP) Duplicate Transmission Sequence Numbers (TSNs) to Detect Spurious Retransmissions

“…Additionally, this document does not outline what a TCP or SCTP sender may do after a spurious retransmission is detected. A number of proposals have been developed (e.g., [RFC3522], [SK03], [BDA03]), but it is not yet clear which of these proposals are appropriate. In addition, they all rely on detecting spurious retransmits and so can share the algorithm specified in this document.…”

“…The Eifel detection algorithm [RFC3522] uses the TCP timestamp option [RFC1323] to determine whether the ACK for a given retransmit is for the original transmission or a retransmission. More generally, [LK00] outlines the benefits of detecting spurious retransmits and reverting from needless congestion control changes using the timestamp-based scheme or a mechanism that uses a "retransmit bit" to flag retransmits (and ACKs of retransmits).…”