Subject: [SIP] Re: [SIPFORUM] Some simple questions

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 19 Jul 2000 00:57:59 -0400

Technical questions on sip actually belong on the sip mailing list,
[email-masked]

anyway, to answer your questions:

Xin Huang wrote:
> 
> I'm new to SIP and have some simple questions. (for page/section please refer to http://www.cs.columbia.edu/~hgs/sip/drafts/draft-ietf-sip-2543bis-00.pdf)
> 
> 1. Is it legal that a UA registers on multiple registrars?

Yes.

> 
> 2. Is header "Max-Forwards" hop-to-hop or end-to-end? On page 35 (Table 4, section 6) it's marked as end-to-end. But on page 50 (section 6.28): every proxy or gateway ... MUST check and update its value ...

Its hop by hop. Thanks for catching this.

> 
> 3. Why should redirect servers support BYE? (on page 27, section 4.2.4)

Proxy and redirect servers are method independent. 

> 
> 4. Why the following headers are not listed in table 3 (page 23, section 3)?
>     Call-Info (defined in section 6.14)
>     Mime-Version (defined in section 6.29)
>     Alert-Info ( defined in section 6.10)

Oversight. THese headers have recently been discussed (in fact, there is
not yet consensus that Alert-Info and Call-Info will stay).

> And, Are "Accept-Encoding" & "Accept-Language" request headers, or general headers? (in table 3 they are general headers, in section 6.8/6.9 they are request headers).

General, I think.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
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[email-masked]                     FAX:   (973) 952-5050
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From: Henning Schulzrinne <[email-masked]>
Date: Wed, 19 Jul 2000 19:49:56 -0400

Jonathan Rosenberg wrote:

> Its hop by hop. Thanks for catching this.

This is actually a bit more complicated in that the SIP hop-by-hop
definition is drifting a bit from the HTTP hop-by-hop definition. In
HTTP, Max-Forwards is considered an end-to-end header for some reason.

> Proxy and redirect servers are method independent.

Modified text to 

  The methods are defined below.  Proxy and redirect servers treat
all     
  methods other than {\INVITE} and {\CANCEL} in the same way,
by           
  forwarding them accordingly. Thus, no method-specific support
is         
  required in these servers for methods other than {\INVITE} and  
{\CANCEL}.

> not yet consensus that Alert-Info and Call-Info will stay).

Indeed. I'm hoping that we'll get this settled in Pittsburgh. Inclusion
in the spec draft is meant to encourage those that dislike their
existence or definition to speak up, in particular since not everyone
that reads the spec subscribes to the mailing list.

> > And, Are "Accept-Encoding" & "Accept-Language" request headers, or general headers? (in table 3 they are general headers, in section 6.8/6.9 they are request headers).

HTTP/1.1 defines them as request headers, but since SIP defines them to
be also applicable to 415, they'd be general headers.

Thanks for catching these discrepancies.