[Sip] RAI-ART Review Comments for draft-ietf-sip-hitchhikers-guide

["Brian Stucker" <[e-mail]>]

Jonathan,

Thanks for putting the document together. It took quite awhile to just
review it! 

Here are the comments that I have as part of the RAI-ART review of the
document. Apologies for the probable repeats in here from list comments,
I was not able to try to correlate my comments with others on the
various reflectors.

I tried to break my comments up by section and document so hopefully
it's coherent in plain-text.

Regards,
Brian

----

Section 1:


   This document itself is not an update to RFC 3261
<http://tools.ietf.org/html/rfc3261>  or an extension to
   SIP.  It is an informational document, meant to guide newcomers,
   implementors and deployers to the SIP suite of specifications.

May want to change "meant to guide newcomers, implementors and deployers
to the SIP suite of specifications" since many of the documents are not
predicated upon SIP itself. For example, RFC-4566, 3388, 3264. Also, I
don't think we want to imply that this document is exhaustive. Perhaps
"It is an information document, meant to introduce newcomers,
implementors and deployers to many of the important IETF specifications
associated with SIP. Specifications referenced by this document were
chosen based on working group consensus and the list presented here is
not intended to be exhaustive or confer any special status over
documents not included."

Might also want to include some pointers to the relevant WG webpages to
give newcomers a place to go for further information. As well as include
some boilerplate about the dangers of implementing I-D's before they
become RFCs (I think this was already discussed somewhat on the RAI
mailing list).



Section 2:

	Although I agree that documents defining relevant registries
should be excluded, what about pointers to the registries themselves?
Seems like some of the interop problems we wind up with are due to
disregard or lack of visibility of the IANA registration process to
implementors.


Section 3:

RFC3261: 

	I think it would be useful to provide a reverse-lookup list of
RFCs that formally update 3261 under the 3261 entry: RFC-3583, RFC-4320
and RFC-4916. There is a statement under 4320 that it formally updates
3261, but there is no mention under 4916 that it formally updates 3261,
it just looks like any other extension. Putting a pointer to the SIPS
work as a TBD formal update to 3261 would also be good as well as
collapsing the "essential corrections to SIP" under the 3261 entry so
that people don't skip over that material would be good as well.

RFC3264:

	Should we perhaps put a pointer here to the offer/answer draft
for further clarification of 3264 since it seems pretty clear that the
baseline specification did not entirely capture all of the interactions
that arise in implementations?

RFC3325:

	May want to remove the word "secure" from the description of the
P-Asserted-ID header description. P-Asserted-ID does not confer any
security of the caller ID information. It's the trust domain that
provides the security in contrast to a mechanism like RFC-4474. 

RFC3581:

	Rport is necessary to routing a response through a NAT, but does
not solve NAT traversal for SIP signaling. Perhaps a pointer to outbound
under this RFC would be useful to highlight what you don't get with
rport that you need to fully address NAT traversal issues, or simply
remove it entirely and rely on folks to go to the NAT traversal section
to discover it there as it's not necessary at all if you have no NATs to
traverse (ALGs and SBCs aside).

RFC4474:

	I don't think it's necessary that we should highlight the
deployment size of the various RFCs in this way, especially given that
the RFC is much newer (and has more complicated requirements) than
RFC3325.

SIPS:

	Should note that this will formally update RFC3261 when approved
to highlight that newcomers should ignore what's in RFC3261.



Section 4:

RFC2848/3910:

	If this has seen little deployment and is very narrowly scoped,
then why are we including it in the guide? 

RFC3372:

	Widespread implementation in a limited deployment model. It
should be noted that it's usage is intended to be temporary as ISUP
endpoints are obviated from the network.

RFC3960:

	Early media is not just generated by the PSTN. We should be fair
here and acknowledge that 3960 does not solve all of the various issues
associated with early media (without enumerating them). We all know this
to be the case, so just a sentence or two should suffice to warn the
reader.

RFC3959:

	We should highlight that this specification has not seen
widespread deployment. As of a few IETFs ago nobody indicated that they
had developed anything with regards to this specification when asked at
a working group meeting. This is only important in that 3960 does not
solve all of the early media issues.


Shouldn't we have an entry in this section for RFC3966 to cover tel
URIs?



Section 5:

RFC3262:

	PRACK is complicated, for sure, but it's used for more than just
PSTN interworking and is more than mildly deployed depending upon the
environment.

RFC3311:

	..but can be used to initiate a reliable request during session
establishment when a re-INVITE is not possible. This is key for
conveying information to an originator that cannot be conveyed in a
response either due to offer/answer complications or because a header is
not allowed in a response message type. We should also point out here
that when UPDATE is used to convey SDP, support for RFC3262 is required
in some scenarios. I don't think this is widely recognized. Should also
call out that it can be used to convey mid-call information as well.

RFC3608:

	You've captured the client perspective of the usage of
service-route, but from a server perspective, it's used by proxies to
capture the route set of a registration to know how to route future
requests on behalf of the client. In this role it has seen greater
deployment and applicability.

RFC 3841:

	Should probably call out the relationship between this RFC and
3840.

Need to remove duplicate entry for SDP negotiation under PSTN
interworking.

RFC4244:

	Should remove reference to voicemail here. It has broader scope.
RFC4758 is intended for this purpose now (later comment).


Shouldn't we have an entry in this section for RFC3880, CPL?



Section 6:

RFC3605:

	Should this be here and under the core specifications section? I
don't see this attribute show up in SDP very often (pre-ICE), but it is
necessary for some NAT traversal solutions. Perhaps only have a
reference to it here? Outside of NAT traversal, is there a primary
reason to have this RFC or ICE in the core specifications section?

OUTBOUND:

	Doesn't outbound satisfy the requirements of a broadly
applicable extension to SIP? Seems like if ICE is a core specification,
that OUTBOUND should be considered one as well?

RFC3890:

	It's used extensively in other SDOs, paricularly wireless.

RFC4730:

	Should probably explain here briefly, that 2833/4733 is most
commonly used to convey DTMF for SIP deployments, but the difference is
that KPML does it on the signaling path as opposed to the media path.
This is somewhat important given the low current deployment of KPML.



Section 13:

	Perhaps we should add an entry here for RFC4896 or make a note
under the entry for RFC3486 that RFC4896 updates both RFC3486 and
RFC3485 which is the static dictionary for SIP (which provides the
explicit coupling between SIGCOMP and SIP eluded to in the draft text).
The important bit for an entry to RFC3485 is that there are a few bugs
in the dictionary such that you'd need to refer to section 12 of RFC4896
to come up with a BCP implementation.



Section 14:

I think we should add an entry for RFC4758 to capture the voicemail
service URI as another important service URI RFC.


Section 15:

RFC3853:

	May want to state that RFC3853 'formally' updates RFC3261, and
put a pointer to this from the core specifications section as a result
since it's a correction to 3261.

RFC3893:

	Should RFC3893 entry simply say something to the effect of 'use
RFC4474', or be dropped altogether?

RFC3329:

	There are now three possible security models now in 3GPP: HTTP
DIGEST, AKA, and early-IMS. As early-IMS doesn't really involve much in
the way of security mechanisms within the SIP protocol, the coexistance
of it with digest or AKA seems to be very probable. Perhaps we should
just remove the last sentence and leave it up to the reader to decide if
it's needed for their purpose.



Section 16:

Shouldn't we perhaps move RFC4796 from section 7 to this section?


Section 17:

Providing a pointer off to ECRIT seems useful here.


That's it!





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