Subject: [Sip] Open Issue #368: Outbound proxy handling

From: Robert Sparks <[email-masked]>
Date: Thu, 24 Jan 2002 22:02:49 -0500

Issue: When a UA is configured to use a default outbound proxy (DOP),
must it use the DOP for requests containing a Route header, or must it
send the request to location indicated by the topmost Route header value?

Discussion: Some UAs will not be capable of sending to the topmost Route.
For example, doing so may require utilizing DNS, which some UAs will not
implement. Such UAs need to use their DOP in this case, and to save
implementation complexity may wish to just send every request to their DOP. 
On the other hand, when the UA is known to support DNS, or in environments 
where the UA can be assured of never seeing a name in the topmost route
header,
it would be advantageous to allow the DOP to choose whether or not to stay
in
the request path by utilizing Record-Route. So requiring all UAs using DOPs
to send every request to the DOP is undesirable.

Resolution: Under loose-routing, this becomes a policy decision for the UA.

The UA will be handed its DOP and potentially a service route (basically,
its loose routing policy) through an agreement with its service provider,
establishing a policy coupling that obligates the service provider to have a

compatible policy at the DOP.

For UAs that are DNS capable, the policy may be to allow the DOP to back out
of requests beyond the initial in the dialog by not record-routing.

For UAs that are not DNS capable, the policy may be to use the topmost route
if it is an explicit IP address, otherwise use the DOP. Alternately, the
policy
may be to send every request through the DOP whether or not it
record-routed.

RjS

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