Subject: [tcpm] Feedback on usage and deployment recommendations in draft-ietf-tcpm-initcwnd-03

From: "Scharf, Michael (Michael)" <[email-masked]>
Date: Fri, 23 Mar 2012 10:47:50 +0100

Hi all,

In the past meetings we had quite some discussion under which constraints it is reasonable to experiment with a larger initial window.

The recently submitted draft-ietf-tcpm-initcwnd-03 includes a new section "12. Usage and Deployment Recommendations" that tries to summarize the concerns expressed by the TCPM community:

   Further experiments are required before a larger initial window shall
   be enabled by default in the Internet. The existing measurement
   results indicate that this does not cause significant harm to other
   traffic. However, widespread use in the Internet could reveal issues
   not known yet, e.g., regarding fairness or impact on latency-
   sensitive traffic such as VoIP.

   Therefore, special care is needed when using this experimental TCP
   extension, in particular on large-scale systems originating a
   significant amount of Internet traffic. Anyone (stack vendors,
   network administrators, etc.) turning on a larger initial window
   SHOULD ensure that the performance is monitored before and after that
   change. Relevant performance metrics include the percentages of
   packet losses or segment retransmissions as well as application-level
   metrics such as data transfer completion times or media quality. Note
   that it is important also to take into account hosts that do not
   implement a larger initial window. Furthermore, non-TCP traffic (such
   as VoIP) should be monitored as well. If users observe any
   significant deterioration of performance, they SHOULD fall back to an
   initial window as allowed by RFC 3390 for safety reasons. An
   increased initial window SHOULD NOT be turned on by default on
   systems without such monitoring capabilities.

   The IETF TCPM working group is very much interested in further
   reports from experiments with this specification and encourages the
   publication of such measurement data. If no significant harm is
   reported, a follow-up document may revisit the question on whether a
   larger initial window can be safely used by default in all Internet
   hosts.

Feedback on this text would be highly welcome.

Thanks

Michael (TCPM co-chair)