Date: Wed, 12 Mar 2003 14:04:22 -0800 From: Jeffrey Hsu <hsu@FreeBSD.org> To: Hiten Pandya <hiten@unixdaemons.com> Cc: src-committers@FreeBSD.ORG, cvs-src@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Re: cvs commit: src/sys/netinet tcp_input.c Message-ID: <0HBN00DUOPABZW@mta5.snfc21.pbi.net> In-Reply-To: Message from Hiten Pandya <hiten@unixdaemons.com> "of Wed, 12 Mar 2003 16:01:07 EST." <20030312210107.GA56887@unixdaemons.com>
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>> hsu 2003/03/12 12:27:28 PST
>>
>> FreeBSD src repository
>>
>> Modified files:
>> sys/netinet tcp_input.c
>> Log:
>> Implement the Limited Transmit algorithm (RFC 3042).
> Can you elaborate on this?
Sure. Quoting from RFC 3042:
The "Limited Transmit" algorithm calls for sending a new data segment in
response to each of the first two duplicate acknowledgments that
arrive at the sender. Transmitting these segments increases the
probability that TCP can recover from a single lost segment using the
fast retransmit algorithm, rather than using a costly retransmission
timeout.
[BPS+97] found that roughly 56% of retransmissions sent by a busy web
server were sent after the RTO expires, while only 44% were handled
by Fast Retransmit. In addition, only 4% of the RTO-based
retransmissions could have been avoided with SACK, which of course
has to continue to disambiguate reordering from genuine loss. In
contrast, using the technique outlined in this document and in
[Bal98], 25% of the RTO-based retransmissions in that dataset would
have likely been avoided.
And from the tcp(4) man page:
tcp.rfc3042 Enable the Limited Transmit algorithm as described in
RFC 3042. It helps avoid timeouts on lossy links.
This is a standards track RFC and is off by default.
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