Re: [Sip] draft-ietf-sip-outbound

["Francois Audet" <audet at nortel.com>]

Let me try to summarize where we are at with the draf-ietf-sip-outbound thread, and let's try
to conclude.

The current text says the following:

   At configuration time, UAs obtain one or more SIP URIs representing
   the default outbound-proxy-set.  This specification assumes the set
   is determined via any of a number of configuration mechanisms, and
   future specifications can define additional mechanisms such as using
   DNS to discover this set.  How the UA is configured is outside the
   scope of this specification.  However, a UA MUST support sets with at
   least two outbound proxy URIs and SHOULD support sets with up to four
   URIs.

   For each outbound proxy URI in the set, the UAC SHOULD send a
   REGISTER request using this URI as the default outbound proxy.
   (Alternatively, the UA could limit the number of flows formed to
   conserve battery power, for example).  UAs that support this
   specification MUST include the outbound option tag in a Supported
   header field in a REGISTER request.  Each of these REGISTER requests
   will use a unique Call-ID.  Forming the route set for the request is
   outside the scope of this document, but typically results in sending
   the REGISTER such that the topmost Route header field contains a
   loose route to the outbound proxy URI.

What Juha is worried about is that there is enough wiggle room in there
that some UAs will not register with the minimum of 2.  It is true
that it is unclear if the text about battery life was meant to allow
for not registering with all the entries in the route set, but still 
keep the minimum of two, or not.

I propose is that the text would look like this:

   At configuration time, UAs obtain one or more SIP URIs representing
   the default outbound-proxy-set.  This specification assumes the set
   is determined via any of a number of configuration mechanisms, and
   future specifications can define additional mechanisms such as using
   DNS to discover this set.  How the UA is configured is outside the
   scope of this specification.  However, a UA MUST support sets with at
   least two outbound proxy URIs and SHOULD support sets with up to four
   URIs.

   For each outbound proxy URI in the set, the UAC SHOULD send a
   REGISTER request using this URI as the default outbound proxy.  
   (Alternatively, the UA could limit the number of flows formed to 
   conserve battery power, for example).  If the set has more than one 
   URI, the UAC MUST send a REGISTER request to at least two of the 
   default outbound proxies from the set. UAs that support this specification 
   MUST include the outbound option tag in a Supported header field in a 
   REGISTER request.  Each of these REGISTER requests will use a unique 
   Call-ID. Forming the route set for the request is outside the scope of this
   document, but typically results in sending the REGISTER such that the
   topmost Route header field contains a loose route to the outbound
   proxy URI.

I think this is reasonable. Basically, what this boils down to is very simple: 
is the minimum number of registration for a proxy set that is bigger than one 2 or 1.
If you are against this proposal, it it is presumably because you believe
a UA should be allowed to use only ONE proxy from the set and ignore the 
second one.

I'd like to get opinions from the list, and close on the issue.



 
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