[SR-Users] Routing re-INVITEs after phone port change

[Alex Balashov]

Hello,

On 08/17/2015 11:22 PM, David Cunningham wrote:

> We have a scenario like this:
>
> SUA -> Kamailio with registrar module -> Asterisk
>
> A call from the SUA is set up with SIP timers, and after 15 minutes
> Asterisk sends a re-INVITE to Kamailio to forward on to the SUA. That
> re-INVITE has a RURI with the address and port of the SUA at the time
> the call started.
>
> Now if the SUA re-registers after the call starts and before the
> re-INVITE, and is on a new address or port number, then the re-INVITE
> never gets to the phone.
>
> Obviously Kamailio should send the re-INVITE to the new address/port,
> but is not. The re-INVITE is routed using the lookup() function.
>
> Can anyone suggest why this is happening?

Reinvites are just ordinary in-dialog requests, and thus should be 
routed as in-dialog requests, in the loose_route() section of the config 
file, i.e.

    if(has_totag()) {
       if(loose_route()) {
          if(!t_relay())
             sl_reply_error();

          exit;
       } else {
          if(is_method("ACK")) {
             if(t_check_trans())
                t_relay();

             exit;
          }

          sl_send_reply("403", "Forbidden");
       }

       exit;
    }

In-dialog requests (including reinvites) should _never_ be routed 
dynamically, e.g. based on lookup(). For dialogs that are established 
through the proxy and where the proxy requests to remain in the path of 
in-dialog requests by adding a Record-Route header, the in-dialog 
requests follow a strictly predetermined path that was computed at the 
time of the establishment of the dialog. This is true of end-to-end ACKs 
(for 2xx replies), reinvites, BYEs, etc.

Additionally, the Request URI of the in-dialog request should be equal 
to the Contact URI of the remote party to the dialog. This is known as 
the "remote target" in standards parlance. It is at the time of the 
initial dialog-forming request routing that all NAT-related 
considerations are computed, e.g. countermeasures for the difference 
between the outward representations made by a party's Contact URI and 
the actual network and transport-layer source from which the initial 
request or reply originated.

So, in short, you shouldn't be doing anything other than the 
abovementioned logic to route a reinvite, notwithstanding RTP pivoting 
measures if using rtpproxy/rtpengine.

-- Alex

-- 
Alex Balashov | Principal | Evariste Systems LLC
303 Perimeter Center North, Suite 300
Atlanta, GA 30346
United States

Tel: +1-800-250-5920 (toll-free) / +1-678-954-0671 (direct)
Web: http://www.evaristesys.com/, http://www.csrpswitch.com/