2 May
2012
2 May
'12
9:07 a.m.
Hello,
OPTIONS out of dialog are ok to detect if the device is gone (e.g.,
network problem -- good for dispatcher case where it needs only to
figure out if gws are up).
Besides this one, I tried to figure out if the dialog is still active in
the end device, by setting dialog's call-id, from-tag and to-tag (e.g.,
like when the device (crashed and) is restarted between keepalives -- it
is still reachable but no dialog anymore). A request with unknown To-tag
should be rejected with 481.
My doubts were related to what would be the behaviour of getting a lower
cseq when dialog is active (callid, from-tag and to-tag mach).
Cheers,
Daniel
On 5/2/12 2:52 PM, Carsten Bock wrote:
Hi Daniel,
we did something similar with Kamailio at Telefonica. But we chose a
little different approach:
Our OPTION-Request was in fact not associated with the Dialog at all,
thus we did not care about correct CSeq or anything at all. We just
sent the OPTIONs to the URI/Routes of the Dialog. All the device had
to do, was to reply in one way or another to that OPTIONs Request.
That worked pretty well with all kinds of Devices, ranging from Zyxel
CPE's, Snom phones, AVM boxes, Asterisk, Symbian built-in and many
more.
Some very rare crappy network devices (i think, we saw this issue only
once, it was a SIP-Client for Symbian, open-source, discontinued)
however simply ignored the OPTIONs, but that was anyway a
non-supported device. Probably, it would also ignore the OPTION
request, if it was with a call-id, cseq, totag, etc.
This is similar to the behaviour used by the Dispatcher module.
Just my $0,02,
Carsten
2012/5/2 Daniel-Constantin Mierla<miconda(a)gmail.com>om>:
--
Daniel-Constantin Mierla - http://www.asipto.com
http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda
Hello,
several days ago, just before freezing the development for v3.3.0, I added
to dialog module the option to send keep alives for ongoing calls in order
to detect if caller/callee is gone.
SIP specs require to increment the CSeq for requests within dialog, but
because the keep alives are sent from the sip server, it would results
de-synchronization of the CSeq values hold in phones themselves (e.g., a BYE
created by caller/callee after a keep alive will be with lower cseq than the
other side would expect and accept). One solution would be to update cseq
when BYE passes the server to the right value. This implies more processing,
as a call can have many re-INVITEs or other requests within dialog sent by
caller/callee, including periodic updates to database to store cseq numbers.
So I went for a different approach, like stated in subject -- let's see your
opinion if you think is going to work. Practically the keep alives will be
OPTIONS with CSeq equal or lower than the last valid value (e.g., the cseq
of the INVITE creating the call).
If the caller/callee is gone, that is simply, the OPTION will be timed out
and dialog module will send BYE.
If the caller/callee are reachable, but for some reason the call was
destroyed (e.g., a crash and restart meanwhile), since there is a To-tag,
the OPTIONS should get a 481 Call/Leg transaction does not exists. Again, a
case when kamailio will end the dialog.
The one to be discussed here would be caller/callee are still on the call.
Based on RFC (and the feedback from people on another thread here), a
requests coming within a dialog with lower CSEq should be replies with 500.
CSeq numbers are still ok in both sides (note that requests with lower CSeq
can happen in reality, like two fast re-INVITEs sent over UDP, the second
arriving first due to network transmission).
I tested with snom phones and jitsi so far, seems to be a working solution
(well, jitsi was replying 500 after 20secs to keep alive OPTIONS request,
not sure for what reason, just reported back to the project).
Is anyone here seeing any possible issues with the approach?
Call are ended by dialog, with proper CSeq in the BYE, after 10seconds from
the moment 408 or 481 is received, no other replies are taken in
consideration for ending the dialog from server side.
Cheers,
Daniel
--
Daniel-Constantin Mierla - http://www.asipto.com
http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda
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