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

From: Bodgey Yin Shaohua <[email-masked]>
Date: Tue, 5 Sep 2000 10:48:16 +0530

Hi,Jonathan: 
    Thank you for your reply.But I also have a puzzle according to your
answer. Let take a example of a successful call flow. (The section 3.1.2 of
draft-ietf-sip-call-flows-01a.txt)

   User A          Proxy 1          Proxy 2          User B
     |                |                |                |
     |   INVITE F1    |                |                |
     |--------------->|                |                |
     |     407 F2     |                |                |
     |<---------------|                |                |
     |     ACK F3     |                |                |
     |--------------->|                |                |
     |   INVITE F4    |                |                |
     |--------------->|   INVITE F5    |                |
     |    (100) F6    |--------------->|   INVITE F7    |
     |<---------------|    (100) F8    |--------------->|
     |                |<---------------|                |

 The F4 is :
   INVITE sip:[email-masked] SIP/2.0
   To: LittleGuy <sip:[email-masked]>
   Via: SIP/2.0/UDP here.com:5060

 The F5 is:
   INVITE sip:[email-masked] SIP/2.0
   To: LittleGuy <sip:[email-masked]>
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=2d4790.1
   Via: SIP/2.0/UDP here.com:5060

 The F7 is:
   INVITE sip:[email-masked] SIP/2.0
   To: LittleGuy <sip:[email-masked]>
   Via: SIP/2.0/UDP ss2.wcom.com:5060;branch=721e418c4.1
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=2d4790.1
   Via: SIP/2.0/UDP here.com:5060

   The Proxy1 and Proxy2 have different host from the there.com, so it may
proxy the message to there.com as indicated in the figure. Or, it may reject
the message with 404 response, so the Call is not successful.  
   In the early version of the Call flow, the Request-URI is the Proxy's
address (ss1.wcom.com for F4 and ss2.wcom.com for F5) which is right
according to your explaining. 
   So I don't which condition is right? If we choose a situation, the
RFC2543 may change somewhat in order to give clear contradiction. 
   Please check it.
   Best regards!
 
Bodgey 

> Bodgey Yin Shaohua wrote:
> 
> 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"? 

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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---

From: Hisham Khartabil <[email-masked]>
Date: Tue, 05 Sep 2000 09:08:00 +0300

The authors of the call flows draft where under the misconception that
the request-uri has to have the proxy server address in the host part.
This was corrected in later releases.

If a proxy server receives a request with the host part matching it
domain, you handle the request by, for example, tooking up registrations
(in the registrar) for that user-name.  If no registrations are found, a
404 is returned, otherwise, the request is forwarded to the address
found in the registrar.

If a proxy server recieves a request with the host part NOT matching its
domain, the server will just forward the request to the host specified
in the request-uri WITHOUT modifying the request-uri.

Regards,
Hisham

Bodgey Yin Shaohua wrote:

>
>
> Hi,Jonathan:
>     Thank you for your reply.But I also have a puzzle according to
> your answer. Let take a example of a successful call flow. (The
> section 3.1.2 of draft-ietf-sip-call-flows-01a.txt)
>
>    The Proxy1 and Proxy2 have different host from the there.com, so it
> may proxy the message to there.com as indicated in the figure. Or, it
> may reject the message with 404 response, so the Call is not
> successful.
>
>    In the early version of the Call flow, the Request-URI is the
> Proxy's address (ss1.wcom.com for F4 and ss2.wcom.com for F5) which is
> right according to your explaining.
>