[SIPForum-discussion] forwarding more than one 2xx in a proxyserver

Robert Sparks rjsparks at nostrum.com
Tue Feb 6 16:53:56 UTC 2007

This is not correct.

Any 1xx message except 100 Trying is an end-to-end message. If the  
INVITE forks, the client
will receive ALL 1xx > 100 sent by any receiving endpoint.

In particular, if the request forks to three places and they each  
send 183s, the client is going to
receive three different 183s (and likely early media from all three  

The relevant section of the spec is RFC3261 section 16.7 subsection 5  
(see page 109).

As an aside - the 1xx messages have no built in recovery from  
transport failure for unreliable transports (UDP).
There is an extension named 100rel (see RFC3262) that adds a  
mechanism to ensure those provisional
messages get delivered if they are really important to the application.


On Feb 6, 2007, at 9:35 AM, vinoth wrote:

> Hi,
>        How will you receive more that 180 Ringing from UASs?.
>        If the Parallel Forking proxy tries more that one end  
> points, it will send you only one Trying to you.
>        And it may recieve more than one Trying, but only one 180  
> Ringing.
>        You will receive only one 180 Ringing only if the  
> destination is reachable(Found) with the help of Parallel Forking.
>   Regards,
> Vinoth Kumar.
> Mobax Networks, Coimbatore, India.
> ---------- Original Message ----------------------------------
> From: "aditi g" <pallavim35 at gmail.com>
> Date:  Mon, 5 Feb 2007 17:00:54 +0530
>> Hi all,
>> I have query regarding forking in SIP.
>> If i am using parallel forking and my proxy recvd more than one  
>> 180 R from
>> UASs.
>> Which 180R will proxy forward to caller.
>> Thanks...
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