Subject: Re: [Tsvwg] Re: [NSIS] interoperability problems between end-to-end ECNandedge-to-edge ECN

From: Sally Floyd <[email-masked]>
Date: Thu, 17 Nov 2005 20:37:51 -0800

Just a note about DCCP's use of ECN: 

DCCP uses ECN by default with both of the currently-defined congestion
control mechanisms, CCID2 and CCID3, unless the end-nodes negotiate
the connection as being ECN Incapable.  The use of ECN Incapable
is "NOT RECOMMENDED".  From Section 12.1 of draft-ietf-dccp-spec-11.txt:

  "ECN incapability both avoids ECN's possible benefits and prevents
  senders from using the ECN Nonce to check for receiver misbehavior.
  A DCCP stack MAY therefore leave the ECN Incapable feature
  unimplemented, acting as if all connections were ECN capable."

That is, the current ECN Nonce is useful to the sender in checking
for receiver misbehavior, in terms of not reporting dropped packets,
even in an environment where none of the routers are ECN-capable.
This is described in Section 9 of draft-ietf-dccp-ccid3-11.txt.

- Sally
http://www.icir.org/floyd/

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