[PCN] Re: WG Review: Congestion and Pre-Congestion Notification (pcn)

Hi Fred,

TCP or "unknown" Pseudo Wire traffic and PCN real time traffic 
will not share the same queues. Your proposal wants to suggest 
a common mechanism resulting in traffic passing one queue to 
be marked by a PCN/ECN codepoint? May be also the determination 
of the rate of congestion marked traffic between an ingress 
and egress edge could be shared. Parts of the feed back mechanism 
between egress and ingress edge may be agreed to. The control 
plane more likely differs, so does the interpretation and 
reaction on a congestion indication. 

Should the above be possible, a router could apply the same 
basic congestion indication and evaluation mechanisms for 
different traffic types. Queuing and the reaction on the 
congestion indication would remain traffic type specific.

Would this rough description point to the right direction?

Regards,

Ruediger

---------Text excerpt from a reply of Fred Baker to Pekka Savola---
# From: Fred Baker <fred at cisco.com>
# Date: Mon, 19 Feb 2007 08:27:30 -0800

I dunno, I think that horse is out of the barn. In the TCP arena, 
the XCP and RCP proposals and RFC 3168 could each be described in 
those terms, and the pre-congestion notification proposals on the 
table all encode congestion information in the IP packets, mostly 
in the ECN field. I'll agree that they should not attempt to 
insert things into the packet (add an option), but using space 
already set aside in the packet needs to be on the table.

I would like to see some crossover between the TCP/SCTP congestion 
control proposals and the real-time pre-congestion proposals. 
That's not a matter of declaring something out of scope as much as 
it is to encourage thoughtful (and not knee-jerk) consideration of 
whether and how the two types of needs can be met.

The drafts I know to be relevant (you'll note that some are in pwe) 
are:

http://tools.ietf.org/html/draft-babiarz-pcn-sip-cap
  "SIP Controlled Admission and Preemption", Jozef Babiarz, 16-Oct-06,
  <draft-babiarz-pcn-sip-cap-00.txt>

http://tools.ietf.org/html/draft-briscoe-tsvwg-cl-architecture
"An edge-to-edge Deployment Model for Pre-Congestion Notification: Admission
Control over a DiffServ Region", Bob Briscoe, 25-Oct-06,
<draft-briscoe-tsvwg-cl-architecture-04.txt>

http://tools.ietf.org/html/draft-briscoe-tsvwg-cl-phb
  "Pre-Congestion Notification marking", Bob Briscoe, 22-Oct-06,
  <draft-briscoe-tsvwg-cl-phb-03.txt>

http://tools.ietf.org/html/draft-briscoe-tsvwg-re-ecn-tcp
  "Re-ECN: Adding Accountability for Causing Congestion to TCP/IP", Bob
  Briscoe, 26-Oct-06, <draft-briscoe-tsvwg-re-ecn-tcp-03.txt>

http://tools.ietf.org/html/draft-chan-pcn-problem-statement
"Pre-Congestion Notification Problem Statement", Kwok Ho Chan, 25- Oct-06,
<draft-chan-pcn-problem-statement-01.txt>

http://tools.ietf.org/html/draft-davie-ecn-mpls
  "Explicit Congestion Marking in MPLS", Bruce Davie, 19-Oct-06,
  <draft-davie-ecn-mpls-01.txt>

http://tools.ietf.org/html/draft-ietf-pwe3-congestion-frmwk
  "Pseudowire Congestion Control Framework", Stewart Bryant, 2-Feb-07,
  <draft-ietf-pwe3-congestion-frmwk-00.txt>

http://tools.ietf.org/html/draft-rosen-pwe3-congestion
  "Pseudowire Congestion Control Framework", Eric Rosen, 19-Oct-06,
  <draft-rosen-pwe3-congestion-04.txt>

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