Simple Lost Retransmission Detection with SACK TCP
draft-scheffenegger-tcpm-lrd-00
TCPM R. Scheffenegger
Internet-Draft NetApp
Intended status: Experimental March 12, 2021
Expires: September 13, 2021
Simple Lost Retransmission Detection with SACK TCP
draft-scheffenegger-tcpm-lrd-00
Abstract
Lost Retransmissions are a major source of latency for TCP transfers.
This note specifies how selective acknowledgment (SACK) information
can be used to timely recover from lost retransmissions. In
addition, it codifies the congestion control reaction on lost
retransmissions.
Note to Readers
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Working Group information can be found at
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Design Considerations . . . . . . . . . . . . . . . . . . . . 4
5.1. Recovery Initiation . . . . . . . . . . . . . . . . . . . 4
5.2. Detection of lost retransmissions . . . . . . . . . . . . 4
5.3. Reordering . . . . . . . . . . . . . . . . . . . . . . . 5
5.4. Ordering of retransmitted segments . . . . . . . . . . . 6
6. Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Lost Retransmission Detection . . . . . . . . . . . . . . 7
6.2. LRD Algorithm Detail . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 10
10.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Appendix A. Lost Retransmission Detection Example . . . . . . . 12
A.1. Lost Retransmission, Mid-Stream . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
Selective Acknowledgement (SACK) is widely used to identify exactly
which TCP segment was lost and only send these missing segments
during a recovery episode. This helps improve the effectiveness of
loss recovery and aligns with the principle of packet conservation.
In addition, SACK information can also be used to infer about lost
retransmissions. When this information is not used, TCP senders
revert to the retransmission timeout (RTO) scheme to recover from
lost retransmissions.
Current SACK implementations, with one widely deployed exception, do
not perform lost retransmission detection. Lost retransmission
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detection (LRD) in the one implementation that performs it was
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