Subject: [SIP] OPTIONS and out-of-band Route.

From: "Fairlie-Cuninghame, Robert" <[email-masked]>
Date: Mon, 6 Nov 2000 19:52:43 -0800

There's seems to be a lot of discussion lately about out-of band Route in
INVITE. Here's a another reason for correct processing of "out-of-band"
Route headers ("out-of-band" with respect to an INVITE initiated call-leg): 

When a UAC makes a OPTIONS request before performing a full INVITE, the UAS
may include a Contact in the 200 OK which be used as the direct destination
to send the initial INVITE. If a proxy needs to be on the path of the
initial INVITE (eg proxy is acting as ALG) then the call will fail if the
proxy and UAC doesn't take some additional action.

DOn't we need to add something such as the following to the spec?

1)A proxy SHOULD insert a Record-Route entry for itself on all OPTION's
requests, if it would have inserted itself on a corresponding INVITE.
2) UAC SHOULD generate a Route header (from the Record-Route in the OPTIONS
response) in the subsequent initial INVITE request if 
	- a Contact header in the OPTIONS 200 OK request is present and
used.
	- a Record-Route header is also present in the OPTIONS response.

[Actually a proxy should only need to insert itself into the Record-Route
header of the OPTIONS _response_ if the response contains a Contact (because
the reverse route will never be needed to an OPTIONS request); however this
just complicates behaviours and so I the above is a better recommendation
for the spec.]

Regards,

Robert.

-- My opinions are my own. I tried selling them once but everybody
	seems to already have one. -- 

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