Subject: [SIP] A question about Request-URI:

From: Bodgey Yin Shaohua <[email-masked]>
Date: Mon, 4 Sep 2000 13:21:49 +0530

Hi: 
      I find a difference among different versons of the draft of SIP
Telephony Call Flow Examples:  Before May 2000, in the Request-URI of SIP
INVITE, there is a address of the Pxory the message will head, but the
version after this time, there is Callee's address the message will head. 
     In section 4.3 of RFC2543, there writes "Typically, the UAC sets the
Request-URI and TO to the same SIP URL, pesumed to remain unchanged over
long time periods", so the latter case is right. But it is difficult to
explain the following word in this section that is "The host part of the
Request-URI typically agrees with one of the host name of the receiving
server. If it does not, the sever SHOULD proxy the request to the address
indicated or return 404 response if it is unwilling to do so".  I don't know
what is meaning of the "receiving server"? If the receiving server is a
proxy server, for the latter case, it may lead to proxy server return 404
reponse and the call fails because the Request-URI is not the address the
Proxy server. 
     Therefore,  it is a fuzzy or an error description. we need give a more
clear description.
     Best regards!

Bodgey Yin
 
Engineering Division
Huawei Technology India Private, LTD
Tel:+91-80-8410061/753/755
Fax:+91-80-8410063
E-mail: [email-masked]

---

From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 04 Sep 2000 23:25:14 -0400

> Bodgey Yin Shaohua wrote:
> 
> Hi:
> Telephony Call Flow Examples:  Before May 2000, in the Request-URI of
> SIP INVITE, there is a address of the Pxory the message will head, but
> the version after this time, there is Callee's address the message
> will head.
> 
>      In section 4.3 of RFC2543, there writes "Typically, the UAC sets
> the Request-URI and TO to the same SIP URL, pesumed to remain
> unchanged over long time periods", so the latter case is right. But it
> is difficult to explain the following word in this section that is
> "The host part of the Request-URI typically agrees with one of the
> host name of the receiving server. If it does not, the sever SHOULD
> proxy the request to the address indicated or return 404 response if
> it is unwilling to do so".  I don't know what is meaning of the
> "receiving server"? 

Its the server that receives the request. 

Perhaps an example will illustrate. Lets say I am making a call to
[email-masked]. I would send an INVITE that looks like:

INVITE sip:[email-masked] SIP/2.0
To: sip:[email-masked]

Now, in one case, I will take example.com, look it up in DNS, and send
it to the IP address of a server I discover through this process. The
example.com server receives the request (it is the receiving server
here). Now, the host part of the request-URI (example.com) matches to
domain of that server (also example.com), so it knows how to handle
requests for this domain.

In another case, I am using a local outboud proxy at dynamicsoft.com.
So, instead of sending the above request there, I send it to the IP
address of the dynamicsoft.com proxy, which my UAC is configured with.
Now, for this proxy, the domain of the request URI (example.com) does
not match the domain of the receiving serer (dynamicsoft.com). So, the
proxy can either forward it to example.com, or reject it with 404.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.cs.columbia.edu/~jdrosen         PHONE: (732) 741-7244
http://www.dynamicsoft.com

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