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List:       sip-implementors
Subject:    Re: [Sip-implementors] tel uri query
From:       Paul Kyzivat <pkyzivat () cisco ! com>
Date:       2007-10-25 13:57:38
Message-ID: 4720A0D2.2080505 () cisco ! com
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Devaki D wrote:
> Hi All,
> I have some doubts regarding the implementation of tel URI as per RFC 3966.Any \
> inputs will be highly appreciated. 
> 1)Is it possible to have tel: URI as request URI in methods other than INVITE and \
> REGISTER i.e in OPTION,PRACK,ACK,CANCEL,BYE, Notify,Subscribe and REFER methods ?

It certainly is possible, with certain limitations.

You didn't specify whether you were considering it in the To header, 
 From header, R-URI, or somewhere else.

Its legal in the From header in all of those methods.

Its legal in the To header in all except REGISTER, which requires a 
sip/sips URI in the To header.

Its legal in the R-URI of all of them.

Of course "legal" from a protocol perspective doesn't guarantee that it 
will yield useful results.

When in the R-URI *somebody* needs to route it to a node responsible for 
that number. *If* the number is resolved to a SIP URI when the request 
is INVITE, then one might expect that it ought to be resolved the same 
way for all methods. But if somebody in the path doesn't support all 
those methods (e.g. if it resolves to a pstn gateway) then many of the 
methods may not work.

Usage of From and To is less standardized, so its hard to predict how 
well tel may be received for some of those.

But the bottom line is: if that is the address you have, then that is 
the one you should use.

IMO TEL isn't used nearly enough. I think it should generally be used in 
cases where the actual address used to originate the request was a "dial 
string" and the URL is derived from the dial string. Turning an 
arbitrary dial string into sip URI by appending a domain name to the 
digits, without any assurance that the domain actually owns the number, 
is common, but wrong headed.

	Paul

> Thanks and Regards,
> Devaki
> 
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