Subject: [mpls] RE: I-D ACTION:draft-ash-avt-hc-over-mpls-protocol-00.txt

From: "Ash, Gerald R \(Jerry\), ALABS" <[email-masked]>
Date: Thu, 21 Apr 2005 17:05:43 -0500

Hi All,

Please review and comment on the (significantly) updated draft "Protocol
Extensions for Header Compression over MPLS"
(http://www.ietf.org/internet-drafts/draft-ash-avt-hc-over-mpls-protocol
-00.txt).

Here is a brief background and overview/explanation of the updates:

Work on requirements for header compression over MPLS
(http://www.ietf.org/internet-drafts/draft-ietf-avt-hc-mpls-reqs-03.txt)
is complete, and work on protocol extensions for header compression over
MPLS is underway (previous draft at
http://ietf.org/internet-drafts/draft-ash-avt-ecrtp-over-mpls-protocol-0
2.txt).  Chartering of the protocol work in the AVT working group has
been submitted for approval with the following milestone:

Dec 05: Submit any extensions for RTP HC on MPLS networks for Proposed
Standard

There has been considerable discussion on the previous protocol
extensions draft
(http://ietf.org/internet-drafts/draft-ash-avt-ecrtp-over-mpls-protocol-
02.txt) in the last couple of months.  I presented the update on the
header compression over MPLS protocol extensions work at the AVT meeting
at IETF-62; slides and minutes are available at
https://datatracker.ietf.org/public/proceeding_interim.cgi?meeting_num=6
2 (look under AVT for minutes and slides).  The recent discussion and
issues regarding the basic approach are summarized in the slides.

Header compression experts in the AVT and ROHC working groups wish to
re-use, and extend, the existing layer 2 approaches for assignment of
context identification (CID) and header compression parameter
negotiation.  In a multipoint-to-point MPLS environment, one approach
would be to have the various header compressors assign CIDs as they do
now, with the possible need to resolve CID conflicts/collisions at the
header decompressor.  Some comments were made that current header
compression methods do not have to resolve CID collisions, however the
synchronization source (SSRC) assigned in RTP could need
collision/conflict resolution.

A second approach, suggested by Andy Malis and Loa Andersson, is to use
pseudowires and/or targeted LDP to create 'point-to-point' sessions
between header compressor and header decompressor, thereby avoiding any
issue of CID collision.  The disadvantage of this approach is that it
requires an additional 4-byte label to be carried with each packet.  

The updated draft based on the second approach is available at
http://www.ietf.org/internet-drafts/draft-ash-avt-hc-over-mpls-protocol-
00.txt.

Once again, please review and comment on the updated draft.

Thanks,
Jerry

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]] On Behalf Of
[email-masked]
Sent: Thursday, April 21, 2005 3:39 PM
To: [email-masked]
Subject: I-D ACTION:draft-ash-avt-hc-over-mpls-protocol-00.txt

A New Internet-Draft is available from the on-line Internet-Drafts
directories.

	Title		: Protocol Extensions for Header Compression
over MPLS
	Author(s)	: J. Ash, et al.
	Filename	: draft-ash-avt-hc-over-mpls-protocol-00.txt
	Pages		: 12
	Date		: 2005-4-21
	
VoIP typically uses the encapsulation voice/RTP/UDP/IP. When MPLS labels
are added, this becomes voice/RTP/UDP/IP/MPLS-labels. For an MPLS VPN,
the packet header is at least 48 bytes, while the voice payload is often
no more than 30 bytes, for example. Header compression can significantly
reduce the overhead through various compression mechanisms.  MPLS is
used to route header-compressed (HC) packets over an MPLS LSP without
compression/decompression cycles at each router. Such an HC over MPLS
capability increases the bandwidth efficiency as well as processing
scalability of the maximum number of simultaneous compressed flows that
use HC at each router.  MPLS pseudowires are used to transport the HC
context and other control messages between the ingress and egress MPLS
label switched router (LSR), and the pseudowires define a point to point
instance of each HC session at the header decompressor.  Standard HC
methods (e.g., ECRTP, ROHC, etc.) are re-used to determine the context.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-ash-avt-hc-over-mpls-protocol-
00.txt

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