Subject: [AVT] Comments on draft-ietf-avt-hc-over-mpls-protocol-01

From: Magnus Westerlund <[email-masked]>
Date: Mon, 31 Oct 2005 11:35:54 +0100

Hi,

I have reviewed the draft and have these comments:

1. In general I think the draft needs a serious editing round. It is 
lacking structure, is confusing and repetitive. In general it doesn't 
read at all as an protocol specification. It is a solution proposal 
which has grown (badly). I would recommend a serious rewrite of the 
document to make it more readable and clear.

2. I also think the incorporation of the usage of Pseudo Wires are not 
consistently done either. Some parts seems to be lacking discussion on 
pseudo wires where I expect it. It might be my lack of knowledge about 
how MPLS and pseudo wires relate.

3. The draft has inconsistent page lengths. Please use draft writing 
tools that ensure a consistent page length.

4. In regards to section 4 I find this section confusing. It is barely 
more detailed then the text in section 3 and contains a lot of 
repetitions. The text is written in informative descriptions rather than 
normative statements on how things shall be done.

5. I also think it focus a lot on the wrong things. It talks a lot on 
context identifiers which is an header compressor to header decompressor 
internal thing, while instead being quite thin on the important parts. 
Sure the information that header compressors can generally handle 
multiple packet flows are fine, but can be left as simple informative 
note. I am missing clear text on how the actual signalling for 
establishing is done. I find sentences like the following clear 
indications that things aren't fully baked yet. Section 4.1, first 
paragraph: "See [PW-SIG] for an explanation of PW signaling, and 
[PW-HDLC-PPP] for a PW type that can be modeled for the application in 
this document."

The use of the word modeled for the application in this document part 
indicates to me that there is need to describe in detail how this should 
be accomplished. I at least are expecting interoperable protocol, not a 
solution outline that manufacturers go implement after their own head.

6. I am also missing the sections with text explaining the variations of 
the process that is needed to make the different HC work. Especially in 
regards how the initial setup signalling for the HC is accomplished. I 
don't think it is sufficient to reference the ROHC or CRTP over PPP 
specs to accomplish that.

7. Section 4.2, what is the scope of the control octet and how does it 
relates to the different types of pseudo wires for HC? To my 
understanding the control octet will be applicable to several of the HC 
mechanisms, however is it guaranteed that they will be the same for all 
of them. Especially if future extensions are develops. Thus should the 
registry for the control octet field be done on a per pseudo wire basis?

8. Section 7, The pseudo wire registration. First of all I think the 
registration should be done by this document as it is this that defines 
the need for pseudo wires and how they are used when established. I also 
find it strange that another draft registers these values prior to 
agreement on this document.

9. Normative references. I have problems with one of the normative 
references. [MPLS-HC-REQS]: This is an informative document that guides 
this solution development process. But it nothing that this 
specification requires for implementation. It is informative and of 
historic nature what requirements that was used for the protocol.

10. Informative references: I noticed RFC 3985 is present in both the 
normative and the informative list.

Cheers

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
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