29 Jan
2010
29 Jan
'10
3:30 a.m.
Klaus Feichtinger schrieb:
The ideal behaviour would be following:
- try reaching a gateway on place B and C until one gateway on every
place (B AND C) sends back a positive (provisional) response - e.g. 180
ringing, 183 session progress
- in case that one of the two parallel addressed gateways is reachable
and sends back a provisional response (= "it is alive"), keep it
- in case that the other one (of the two parallel addressed gateways)
has a problem (negative response 480 / 404 / 486 ...) or is unreachable
(= |fr_inv_timer_next| timeout), try the next gateway on this specific place
I'm still not sure if I understand it correct. May examples help:
the call is forwarded to B1 and C1. B1 does not send back anything, C1
sends back 100 trying. What is the expected behavior?
- CANCEL C1 and send the call to B2 and C2?
- keep C1 and send another call to B2?
- stay with B1 unreachable and possible C1 answering the call?
Hi,
I have a special question regarding a mixture of parallel and serial
forking, operated by Kamailio-3.0.0.
First of all I will give you a short background information, what the
target will be:
I have a SIP-server on place A, 3 gateways on place B and 3 gateways
on place C). These gateways are registered on SIP server (A) with
different Q-values (e.g. GW-B1=1.0, GW-C1=1.0, GW-B2=0.8, GW-C2=0.8,
GW-B3=0.6, GW-C3=0.6). The target is, that a call for a gateway MUST
be signalled on place B and C in parallel (forking) until the call is
finally established over one of the two involved gateways on place B
or C. When the prime gateway(s) (with the highest Q-value) fail (e.g.
they do not send a provisional response within a timeout or send a
negative response), the next gateway(s) should be addressed (with the
next lower Q-value), a.s.o.
The configuration works well in case that both gateways on place B
and C fail at the same time (BOTH do not send a response or BOTH send
a negative response or one does not send a response and the other one
sends a negative response). However, in case that only ONE of the two
(always in parallel) addressed gateways fails, it does not work as
expected.
What is expected?
Do you want to trigger failover to lower priority even if one the
gateways is still working fine? You can not do that with sip-router.
sr implements parallel forking according to RFC3261, this means it
will not generate a failure response as long as one of the branches is
still active, maybe sending 200 ok.
- the parallelism is necessary, because calls over
these gateways are
addressed to a usergroup which is split to place B and C behind a
redundant "non-SIP" PBX system with two active halfs); you can not
suspect if a user on place B or a user on place C will take the call;
therefore the call has to be sent to both places.
Ok.
However, the favored behaviour is not standard conform
- I know. I guess
therefore I would need a B2BUA, which is able to establish two
independent (serially forked) preliminary connections to gateways on
place B and C and interconnects the successful call to the call
originator. I fear that no possibility will be available with Kamailio /
a standard SIP server.
Maybe you can achieve the wanted behavior by modifying tm module to
CANCEL all branches if a single branch fail (similar to processing of
6xx error response, which also cancels all branches).
Depending on the exact needed behavior you might be able to do it with
Asterisk.
regards
klaus
The easiest way would be forking the incoming call to ALL available
gateways in parallel. Any gateway will accept the call. However, this is
not supported by the gateways and the system behind the gateways yet.
Does anybody have an alternative idea to parallel forking, how this
"requirement" could be solved?
regards, Klaus F.