Pang Xiaogang-r63373 wrote:
Hi Paul,
I have doubt of the URI: <sip:[EMAIL PROTECTED];user=phone>
Say I have 2 Uas and registered to different registrar with different phone number
UA1: <sip:[EMAIL PROTECTED];user=phone> UA2: <sip:[EMAIL PROTECTED];user=phone>
Well, you hit at the heart of the matter. If you are going to dial numbers then *somebody* has to figure out what domain the recipient resides in.
ENUM is the recommended solution to this problem. I suggested the above only in the case when there was a desire to avoid ENUM.
However there are solutions even in the case you cite. Writing the addresses that way imposes a domain for purposes of routing. But once the request arrives at the specified domain, the receiving server knows that the address is a phone number. Through local knowledge it can decide if this is a phone number that it is responsible for. If not, it can rewrite the address and forward it on elsewhere via sip, or it can pass it to a PSTN gateway.
If UA2 makes a call to UA1, it dials "1234", but how can it decide UA1's domain? (i.e. sip.freescale.com.)
There is a separate issue of you a dial string of "1234" is converted in a URL of any form (tel: or sip:). Clearly this must be done before an address can be sent. The UA must have some local knowledge to do this, in the form of a dial plan with rewrite rules.
After must discussion, there was a decision to create yet another form of sip url to specifically convey a dial string, as distinguished from an actual phone number. This can be used when the UA desires that a proxy contain the logic for converting dial strings into unique phone numbers. Using this, UA2 would initiate the request with:
<sip:[EMAIL PROTECTED];user=dialstring>
and it would be up to the freescale.com server to figure out what UA2 really meant by this - applying some sort of dial plan to expand this to either a tel url or another sip url. For instance, based on local knowledge, freescale.com might decide to translate this to:
<sip:[EMAIL PROTECTED];user=phone>
Paul
Regards,
David
[EMAIL PROTECTED]
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-----Original Message-----
From: Paul Kyzivat [mailto:[EMAIL PROTECTED] Sent: Thursday, September 09, 2004 8:57 PM
To: [EMAIL PROTECTED]
Cc: Xiaogang Pang; [EMAIL PROTECTED]; Jacob Zhu
Subject: Re: [Sip-implementors] REGISTER with a Tel uri
[EMAIL PROTECTED] wrote:
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Behalf Of ext Paul Kyzivat
Sent: 08.September.2004 22:24
To: Pang Xiaogang-r63373
Cc: [EMAIL PROTECTED]; Zhu Jacob-r62823
Subject: Re: [Sip-implementors] REGISTER with a Tel uri
If you want to avoid ENUM, then you should probably avoid
tel: as well. Instead, use sip uris with the user=phone parameter:
REGISTER: sip:freescale.com To: <sip:[EMAIL PROTECTED];user=phone> From: <sip:[EMAIL PROTECTED];user=phone> Contact: sip:[EMAIL PROTECTED]
I don't know what value user=phone adds here.
Its value is to say that what is in the user part is a phone number. 3261 has defined two namespaces for the user part, distinguished by the value of the user parameter, so it is good to be clear about which namespace is being used.
Of course many systems don't really have two namespaces, and instead treat them as equivalent. If so, then it doesn't matter if you specify it or not. But unless the UA is certain about the conventions of the registrar it is safe to be explicit.
Paul
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