[AVT] Commetns on Header compression for MPLS LSPs (draft-ash-avt-ecrtp-over-mpls-protocol-00.txt)

[Magnus Westerlund <magnus.westerlund at ericsson.com>]

Hi,

Having reviewed the solutions proposal document I would like to take a 
few steps back, and discuss the issues on a higher level. We should also 
not be carried into to much detail yet until the requirements work is 
completed.

In my understanding we will need a few components in the total system.

A. A signalling protocol for an MPLS ingress router (A) to 
determine/create the LSP that will go to a HC enabled egress router (B). 
That protocol seems to need to signal the following information:
- What HC algorithms it support
- What LSP that will go from A->B and for HC algorithms that uses 
feedback the return path B->A, which indicates HC enabled packets.
- Further HC algorithm parameters, for example maximum number of session 
contexts.

B. To create a mapping for the HC algorithm into the LSP. Here it seems 
that ECRTP would need to have identifiers for its packet types, while 
ROHC would not need anything.

The solution does not require anything more as I see it. It can be 
enhanced with description of how an ingress router determines what flows 
to do HC on, for example through the header compression hints that exist 
for RSVP, see RFC 3006. An ingress router can also use heuristics or any 
other method it desires to determine if it should apply header 
compression on a certain packet flow. Thus I don't see a need to talk 
about specific applications of RTP or UDP that can benefit from this work.

Something else that I reacted to in the draft was the indication that 
one needs to actually use a signalling session context identifiers. As I 
understand it, a compressor simply selects one from the available pool 
and establish it using a full context packet.


Cheers

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
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