RE: [Sip] Outbound issues: slides 9 and 10 - Why does every proxy need to support outbound?

["Christer Holmberg \(JO/LMF\)" <christer.holmberg at ericsson.com>]

Hi,

A couple of questions:

>The issues on slide 9 (how does a registrar verify that an edge proxy
supports outbound) and slide 10 (what does >"Supported: outbound" mean)
deal with detecting that all the required hops support outbound.  Slide
>9 specifically uncovered a problem with outbound proxies that add a
Path URI but don't include a flow token.
>
>The proposed solution is as follows.  If a proxy inserts a Path header
with a flow token consistent with the rules d
>escribed in outbound, it MUST add the ;ob parameter to the proxy URI
that has the flow token.
>
>The registrar verifies that any Path header URIs contain the ;ob
parameter.  If there are any Path URIs without the ob 
>parameter, the registrar does not return Supported: outbound.

[CHH] Why would every Path header need to contain the ;ob parameter? The
REGISTER request may traverse, in addition to the outbound proxy,
multiple proxies which insert a Path header. Do all these proxies really
need to support outbound?

>Furthermore, the registrar needs to check that the first hop after the
UAC is represented in the Path list (unless the 
>registrar recognizes that the first hop after the UAC is in the same
domain and doesn't need to include Path URIs with a 
>flow token).  Note that this implies that whatever the proxy puts in
the Via (IP address or FQDN), it must put the same 
>hostname in the Path header (but there is no need for a complete URI
comparison).  If the first hop is not correctly 
>represented, the registrar ignores the reg-id parameter and does not
return Supported: outbound.

[CHH] Isn't it much easier to mandate the outbound proxy to always
insert a Path header?

OR, another possibility is that the outbound proxy, if it detects that
the UAC supports outbound, insert some option-tag of itself in the
Supported header, to indicate to the registrar that it supports
outbound. Then the registrar does not need start looking at the Path
headers.

Regards,

Christer








The implication of this is that an outbound-proxy that supports outbound
needs to support Path and flow tokens for registrations to all foreign
domains.  Inside the same domain, the first-hop proxy and the registrar
can still use Path to communicate with each other, but they can use some
other private mechanism to disaggregate this functionality.

thanks,
-rohan


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