Hi,

Actually, this won't help for attended transfers where another call is initiated first then the two are joined together by REFER. In this case, the second INVITE must be routed to the same media server as the existing call for the transfer to work.

What we do is store the dialogs in DB, then when a new call comes in, prior to doing ds_select_dst we query DB for existing call involving same user. If we find one, we simply replace destination host with that from the contact (to/from depending on direction of call).

It may not be the most elegant way but it works for us :)

Charles

-----Original Message----- From: sr-users-bounces@lists.sip-router.org [mailto:sr-users-bounces@lists.sip-router.org] On Behalf Of Carsten Bock Sent: 26 April 2012 13:25 To: SIP Router - Kamailio (OpenSER) and SIP Express Router (SER) - UsersMailing List Subject: Re: [SR-Users] dispatcher and call transfer

Hi,

if you look at the docs of the dispatcher module, you'll find this:

alg - the algorithm used to select the destination address. The parameter can be an integer or a variable holding an interger. - “0” - hash over callid (http://kamailio.org/docs/modules/devel/modules_k/dispatcher.html#id2498492)

But probably you should look into record/loose_route for your setup. Since REFER is normally an in-dialog request (belongs to another voice-session), it should take the same route as the initial INVITE. This is normally achieved by the record/loose-route mechanisms described in RFC3261. In the example config of Kamailio you find an configuration example (below).

It is not a bug in the dispatcher module, it's how you use it.

So long, Carsten

455 # handle requests within SIP dialogs 456 route(WITHINDLG);

[...]

473 # record routing for dialog forming requests (in case they are routed) 474 # - remove preloaded route headers 475 remove_hf("Route"); 476 if (is_method("INVITE|SUBSCRIBE")) 477 record_route();

and the relevent parts in the "WITHINDLG" route:

566 # Handle requests within SIP dialogs 567 route[WITHINDLG] { 568 if (has_totag()) { 569 # sequential request withing a dialog should 570 # take the path determined by record-routing 571 if (loose_route()) { [...] 580 route(RELAY); 581 } else { [...] 587 if ( is_method("ACK") ) { 588 if ( t_check_trans() ) { 589 # no loose-route, but stateful ACK; 590 # must be an ACK after a 487 591 # or e.g. 404 from upstream server 592 t_relay(); 593 exit; 594 } else { 595 # ACK without matching transaction ... ignore and discard 596 exit; 597 } 598 } 599 sl_send_reply("404","Not here"); 600 } 601 exit; 602 } 603 }

2012/4/26 Asgaroth 00asgaroth00@gmail.com:

Hi All,

Currently we are running kamailio in a loadbalanced fashion whereby calls come in via the loadbalancers and distribute calls accross 2 media

servers.

We have come accross and issue whereby call transfers may be distributed accross two media servers and when the REFER message comes along to

transfer

the call, in some cases (if we're lucky) the message arrives at the wrong media server (transaction leg doesnt exist).

Some googling later and it appears that dispatcher doesnt play nice when

it

comes to this scenario. Some suggestions popped up in my previous searches saying that a potential work around is to use the dialog module to check

if

a call is eastablished and then to send all calls to the same media server based on the dialog already being established.

I'd appreciate some input from the guru's out there that have come accross this same issue and, if possible, some suggestions on how to work around

the

problem, does the dispatcher module have a hashing algorithm that can be suited for this particular scenario?

Thanks in advance for any tips or sugestions.

---

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