Subject: [BEHAVE] TURN 07: Congestion control interaction issues

From: Magnus Westerlund <[email-masked]>
Date: Sun, 09 Mar 2008 00:20:09 +0000

Hi,

I realized that Turn needs to document and warn about another issue when 
using TCP between TURN client and server. That is the congestion control 
interactions between the relayed stream and the TCP transport. It is 
well known that TCP in TCP can result in really bad throughput behavior. 
Similar issues could arise for what ever adaptation or congestion 
control one uses for the UDP media stream when being transported over TCP.

Cheers

Magnus Westerlund

IETF Transport Area Director & TSVWG Chair
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From: "Dan Wing" <[email-masked]>
Date: Tue, 11 Mar 2008 16:03:44 -0400

> control one uses for the UDP media stream when being 

That is a good point.  

SSH is perhaps 'the' classic protocol that does TCP-over-TCP, yet it does not
appear to say anything regarding congestion, loss, or drop in its 5 RFCs:

  grep -iE "congest|loss|drop" rfc4250.txt rfc4251.txt rfc4252.txt rfc4253.txt
rfc4254.txt
  rfc4251.txt:                      "Telecom Glossary 2000", ANSI T1.523-2001,
  rfc4254.txt:   only set environment variables after the server process has
dropped

I'm not saying that because ssh was silent on this matter that TURN should be
silent.  But I don't think TURN can be expected to _solve_ the reaction of two
back-off mechanisms when a single packet loss occurs in the UDP-over-TCP
tunnel.

Are you aware of a citation we could use in TURN, where this interaction
between competing back-off mechanisms is described?

-d