Subject: RE: [Sipping] Diversion header

From: Adam Roach <[email-masked]>
Date: Mon, 28 Jul 2003 17:38:47 -0500

Cullen Jennings [mailto:[email-masked]] writes:

> Give some careful thought to if the "To" header meets your
> needs and if it does use - The To header is widely implemented :-)

There are some heavy caveats to be noted here.

Of primary note is that the "To" header is merely going
to represent what URI the UAC thought it was sending the initial
request of the call to. This may or may not be something that
makes sense in your context.

Consider, for example, that my device might have an interface
that most comfortably allows me to input numerical digits. It
then takes these digits and, by default, sends them to a proxy
local to my site. I have, in this example, set up my local
proxy to take any one- or two-digit extensions, perform
a lookup in a local "speed dial" table, and retarget the
request accordingly.

In this case, you may well get a request with a "To"
header field like: "To: <tel:14>" or
"To: <sip:[email-masked]>". That probably
doesn't get you quite as much information as you'd
like, since the mapping of the "To" field to anything
relevant to anyone other than me isn't something you have
access to.

Myriad other such cases exist.

So, while Cullen is right that you can (generally) look
at the "To" header to find out what the original response
Request-URI probably was, the practical truth is that
you typically can't rely on that information to be useful
from a service perspective.

/a

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