Subject: [Sip] Question on record-routing with outbound proxy

From: Itamar Gilad <[email-masked]>
Date: Wed, 25 Jul 2001 10:10:03 +0300

Hi,

reading bis-03 16.4.1 raises some questions:

"16.4.1 Local outbound proxies
Special considerations exist for local outbound proxies.
A UA which uses a local outbound proxy will send all requests without Route
headers to that proxy. Typically, this includes initial INVITE requests for
a call."

Q: All requests? Doesn't that break record-routing and contradict the rest
of this paragraph? What am I missing?

"If a local outbound proxy wishes to remain on the SIP messaging path for a
call leg, it MUST record-route using the procedures above.
A UA which uses a local outbound proxy, and attempts to send a subsequent
request in a call leg with a route set, SHOULD use the procedures in Section
16.4."

Q: does that mean circumventing the outbound proxy? It does judging from the
next sentence.  Using local outbound is the topic of this paragraph so I
guess this sentence is redundant.

"However, in some instances, a UA may not be capable of DNS, and therefore
may not be able to follow those procedures. In this case, the UA MAY send
the request to its local outbound proxy."
In this case, it MUST NOT remove the top Route header. It sets the
Request-URI to the same value it used for the initial request, and sends it
to its local outbound proxy."

Q: how is a UA (especially one lacking DNS capabilities) supposed to know
that its outbound proxy is record-routing?  The proxy may use in the
Record-Route header a different address than the one the UA knows it by.  

Thanks,
 
Itamar Gilad
RADVISION
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---

From: Christer Holmberg <[email-masked]>
Date: Wed, 25 Jul 2001 11:20:12 +0300

Hi Itamar,

>of this paragraph? What am I missing?

Like you wrote, the text says "all requests WITHOUT Route", ie no proxy
has inserted Record-Route.
 
I do have a question related to this, though:

Assume that a remote party sends an INVITE to my client. There are no
proxies in the path, so there will be no Record-Route. There is, of
course, the mandatory Contact header. Then my client answers, and
receives ACK. Nothing strange so far.

Later, my client wants to release the call, so it sends a BYE. My client
is configured to use an outbound proxy, so:

Q: Since there is no Route, shall it send the BYE to the outbound proxy,
or directly to the remote client (defined in the Contact my client
received in the INVITE)?

Q: My understanding of the text is that the BYE should send it to the
outbound proxy. Could someone confirm that? 

Q: Also, could this cause some problem if the outbound proxy is
stateful, since it will receive a BYE it never received an INVITE for?

Regards,

Christer Holmberg
Ericsson Finland