[SR-Users] dispatcher and call transfer
Asgaroth
00asgaroth00 at gmail.com
Fri Apr 27 12:44:07 CEST 2012
Thanks all for the suggestions.
@Charles
Yes that is correct, that is the scenario that is occurring, we are
using asterisk, when a call is initiated via asterisk 1, the second call
then routes through to asterisk 2, asterisk 1 then gets the REFER but
doesn't know about the 2nd call.
@Reda
I like this option of using the hash table (I'd like to exclude a
database lookup for each initial invite), however, would I be forced to
use a database in the case of 2 loadbalancers, surely some shared state
would need to exist between the loadbalancers to make this decision on
where to route the call if it already exists. I suspect the hashtable
suggestion may work perfectly in a single loadbalancer scenario, unless
I'm missing something. For example, the initialy call may go via
loadbalancer 1 however the second call may go through loadbalancer 2,
that way loadbalancer 2 may not know of an existing call already been setup.
In keeping with the hashtable train of thought, is it really neccessary
to keep a reference to the callid, as the second call in the transfer
scenario described by Charles, the callid of the second call is
different to the original call.
Just as an FYI, I am currently using dispatcher algorithm 0 which is a
hash over callid.
Thanks again all for the suggestions/tips
On 26/04/12 16:12, Charles Chance wrote:
>
> Yes, I realise Asterisk is not a media relay, but I don't think the OP
> is using a pure media relay, otherwise the REFER message would not be
> sent to it, would it?
>
>
>
> Thank you for the hash table suggestion by the way.
>
>
>
> Charles
>
>
>
> ------------------------------------------------------------------------
>
> *From:*sr-users-bounces at lists.sip-router.org
> [mailto:sr-users-bounces at lists.sip-router.org] *On Behalf Of *Reda Aouad
> *Sent:* 26 April 2012 15:15
> *To:* SIP Router - Kamailio (OpenSER) and SIP Express Router (SER) -
> UsersMailing List
> *Subject:* Re: [SR-Users] dispatcher and call transfer
>
>
>
> Asterisk is not really a media relay. Asterisk establishes 2 legs for
> each call, and I'm not sure what happens in this case.
>
> An improvement you can make is to use a hash table (in-memory) to
> store the information you need (call-id, from, to) then lookup in
> the htable for existing calls for same users. That should relieve your
> database from a query on every invite and increase performance if you
> have a large number of calls.
>
>
>
> Reda
>
>
>
>
>
> On Thu, Apr 26, 2012 at 15:52, Charles Chance
> <charles.chance at sipcentric.com <mailto:charles.chance at sipcentric.com>>
> wrote:
>
> Hi Reda,
>
>
>
> Sorry, I should have been more specific -- I am referring to instances
> where the media server is for example Asterisk. If first call goes
> through Asterisk 1, second call goes through Asterisk 2, when Asterisk
> 2 receives the REFER it does not know of initial call on Asterisk 1.
> The only way we have found for it to work is to ensure the second call
> is dispatched to the same Asterisk box as the first.
>
>
>
> I would be pleased to hear of an alternative method.
>
>
>
> Regards,
>
>
>
> Charles
>
> ------------------------------------------------------------------------
>
> *From:*sr-users-bounces at lists.sip-router.org
> <mailto:sr-users-bounces at lists.sip-router.org>
> [mailto:sr-users-bounces at lists.sip-router.org
> <mailto:sr-users-bounces at lists.sip-router.org>] *On Behalf Of *Reda Aouad
> *Sent:* 26 April 2012 14:34
>
>
> *To:* SIP Router - Kamailio (OpenSER) and SIP Express Router (SER) -
> UsersMailing List
> *Subject:* Re: [SR-Users] dispatcher and call transfer
>
>
>
> Hi,
>
> @Carsten
> Dispatcher algorithm 0 based on call-id should do it in your case of
> re-invite within dialog with same call-id.
>
> @Charles
> In the case of attended transfers, shouldn't both media servers be
> relaying media between them? I didn't understand why your are obliged
> to dispatch to the same media server since they are 2 different calls
> with different call-ids.
>
>
>
> Reda
>
>
>
>
>
> On Thu, Apr 26, 2012 at 14:30, Charles Chance
> <charles.chance at sipcentric.com <mailto:charles.chance at sipcentric.com>>
> wrote:
>
> 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 at lists.sip-router.org
> <mailto:sr-users-bounces at lists.sip-router.org>
> [mailto:sr-users-bounces at lists.sip-router.org
> <mailto:sr-users-bounces at 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 at gmail.com
> <mailto:00asgaroth00 at 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.
> >
> > _______________________________________________
> > SIP Express Router (SER) and Kamailio (OpenSER) - sr-users mailing list
> > sr-users at lists.sip-router.org <mailto:sr-users at lists.sip-router.org>
> > http://lists.sip-router.org/cgi-bin/mailman/listinfo/sr-users
> >
>
>
>
> --
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> CEO (Geschäftsführer)
>
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