From: "Xiaoliang \(David\) Wei" <weixl@caltech•edu>
To: <netdev@oss•sgi.com>
Subject: A question on RTT estimation of SACKed packet.
Date: Thu, 29 Aug 2002 03:17:24 -0700 [thread overview]
Message-ID: <037601c24f45$4549fe10$f1fa010a@weixl> (raw)
In-Reply-To: 20020828074112.A13868@nero.doit.wisc.edu
Hi Everyone,
I am studying the Linux 2.4.19 TCP code. I have a question on the RTT
estimation.
In the function tcp_clean_rtx_queue (tcp_input.c), all the packet before
snd_una is checked:
1. When a packet was not SACKed before, we can calculate the seq_rtt
from its skb's timestamp (now - scb->when).
2. When a packet was SACKed but not retransmitted, the linux also
calculate the seq_rtt from it when there is no unSACKed packet in the queue.
I cannot understand the second situation: The packet was SACKed before,
that means it arrived the receiver and triggered a SACK sometime before. The
interval between when packet is sent and when the SACK is received should be
the RTT for experienced this packet. Even now the packet is ACKed, I don't
think this ACK is triggered by this packet. Why is it used to calculate the
RTT?
Thanks.
-David
Xiaoliang (David) Wei Graduate Student in CS@Caltech
http://www.cs.caltech.edu/~weixl
====================================================
next prev parent reply other threads:[~2002-08-29 10:17 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-06-24 11:39 IP stack question Bloch, Jack
2002-06-24 13:34 ` jamal
2002-06-24 17:48 ` Ben Greear
2002-06-24 18:59 ` jamal
2002-06-24 19:27 ` Ben Greear
2002-08-28 6:25 ` IP stack question (how to force pkts to not route locally, but go out interfaces regardless of destination) Ben Greear
2002-08-28 12:41 ` James R. Leu
2002-08-29 10:17 ` Xiaoliang (David) Wei [this message]
2002-08-29 19:01 ` A question on RTT estimation of SACKed packet kuznet
2002-08-29 22:19 ` Xiaoliang (David) Wei
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='037601c24f45$4549fe10$f1fa010a@weixl' \
--to=weixl@caltech$(echo .)edu \
--cc=netdev@oss$(echo .)sgi.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox