Ideally I think Kamailio should send correct (i.e increasing) CSeq numbers.

in my mind it can't be increased by kamailio because of: 1. kamailio send OPTIONS with cseq+1 2. media server may send some indialog reinvite with cseq+1 and then kamailio have to remember that OPTIONS and translate reinvite to cseq+2.

I don't know why for "ka-src" CSeq is 0 and for "ka-dst" the one is equal: so may be it is possible to be fixed

(for example BYE) to be dropped by the firewall.

this may be achieved by 1. usrloc pinging 2. short re-registration period for endpoint (60 sec for ex) 3. let's media server send options by itself via kamailio

2018-04-16 15:37 GMT+03:00 Oded Arbel odeda@cloudonix.io:

On Mon, Apr 16, 2018, 14:59 Dmitri Savolainen savolainen@erinaco.ru wrote:

...

hi

Indeed dialog OPTIONS are send with wrong CSeq and there is no way to fix it without patching source.

...

In docs for dialog module "If keep alive is enabled for a dialog, the module will send SIP OPTIONS requests with CSeq lower or equal than last request within dialog"

Yes, I've read this - but why?

Usually Kamailio is used before some media server (asterisk,

...

freeswitch...): endpoint1 - kamailio ----leg1---- media_server ---leg2---- kamailio - endpoint2

So if it is your case

This is indeed my case.

you want to check if dialog alive, you may ping media server instead of

...

pinging remote endpoints

I don't want to use "keep alive" to *check* if the dialog is alive - I want to use "keep alive" to keep the dialog alive, or more precisely: to prevent the MUA's NAT from tearing down the port mappings it creates when the MUA starts the dialog, for as long as the call is alive.

For that I need to set:

For leg1: dlg_set_propery("ka-src"); For leg2: dlg_set_property("ka-dst");

And then the MUAs need to be able to respond. Even a 500 error response is enough for Kamailio to mark the message as received successfully and to keep sending OPTIONS messages, and as I described in my email, this sometimes works for "ka-dst", but for "ka-src" Kamailio always sends CSeq 0 to the MUA - as a result the MUA does not respond, causing Kamailio to retry a few times until it gives up, stops sending keep alive messages, allowing the NAT to teardown the SIP port mapping causing the next server originated message (for example BYE) to be dropped by the firewall.

Ideally I think Kamailio should send correct (i.e increasing) CSeq numbers. I think I can submit a patch to fix this, but as the current behavior is (more or less) documented I would want to understand why some one thought it's a good idea before attempting to change it.

...

2018-04-12 23:34 GMT+03:00 Oded Arbel odeda@cloudonix.io:

...

Hi all.

I'm trying to use the dialog module's keep alive feature (ka_interval() and dlg_set_property()), and the documentation (under dlg_set_property) says this:

If keep alive is enabled for a dialog, the module will send SIP OPTIONS requests with CSeq lower or equal than last request within dialog

This is seems really weird to me, but the problem is worse than that - when setting dlg_set_property("ka-src"), the OPTIONS messages sent to the caller always have CSeq set to "0", regardless of what CSeq the UA sent on its invite.

The problem is that while some UAs respond to these purposefully broken messages with some kind of a 5xx reply (for example, Linphone funnily sends "500 Internal Server Error"), several UAs don't respond at all. Worse than that - some of the UAs that send back 5xx replies to OPTIONS with a non-zero but invalid CSeq will completely ignore the OPTIONS keep-alive message that is sent to the caller with a CSeq 0 - for example, PJSIP responds with "503 Invalid CSeq" to a "ka-dst" OPTIONS message but will ignore a "ka-src" OPTIONS message with CSeq 0.

My questions:

1. Why are keep-alive messages sent with a wrong CSeq?
2. If we're keeping the "wrong CSeq" approach, can we at least not send

CSeq "0"? 3. Is there a way to change any of the above behaviors with a configuration (i.e. without patching the sources)?

Thanks in advance

-- Oded Arbel odeda@cloudonix.io

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-- Savolainen Dmitri _______________________________________________ Kamailio (SER) - Users Mailing List sr-users@lists.kamailio.org https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users

--

Oded Arbel oded.arbel@greenfieldtech.net [image: Greenfield Tech] http://greenfieldtech.net/

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Hello,

the keepalive is done via sort of a trick which needs to detect:

- if one side is no longer connected to the network -- keepalive results in retransmission timeout

- if one side is no longer knowing the dialog - so call-id, to-tag and from-tag values do not match -- keepalive results in 481 Call Leg/Transaction Does Not Exist

Any other case is not relevant for the keepalive purpose of detecting if a side is still in the call.

Therefore, CSeq is intentionally set to an lower value than expected by each side, in order not to impact what is sent by each side.

If you want to do nat keepalive for the duration of the dialog, that can be achieved by using nat_traversal. Or if you use a location service, usrloc+nathelper does it for the registration session.

Cheers, Daniel

On 17.04.18 08:25, Oded Arbel wrote:

On Mon, Apr 16, 2018, 16:24 Dmitri Savolainen <savolainen@erinaco.ru mailto:savolainen@erinaco.ru> wrote:

    Ideally I think Kamailio should send correct (i.e increasing)
    CSeq numbers.

in my mind it can't be increased by kamailio because of:
1. kamailio send OPTIONS with cseq+1
2. media server may send some  indialog reinvite with cseq+1 and
then kamailio have to remember that OPTIONS and  translate
reinvite to cseq+2.

Fair point, statelessness is important.

I don't know why for "ka-src" CSeq is 0 and for "ka-dst"  the one
is  equal: so may be it is possible to be fixed 

I'll investigate, under the assumption everyone agrees it's a bug.

     (for example BYE) to be dropped by the firewall.

this may be achieved by
1. usrloc pinging

I'm not sure that is usrloc pinging, but if you mean nathelper's nat_ping, then that wouldn't work for me because it's only for MUAs that use REGISTER, which on my system does not always happen.

2. short re-registration period for endpoint (60 sec for ex)

Aside from the fact that REGISTER is not guaranteed to ever happen, this is also a UA setting that can't be enforced by the server and has serious implications on battery life outside of a call.

3. let's media server send options by itself via kamailio

This may or may not be possible on my setup, I'll have to investigate

• thanks for the suggestion!

--

Oded Arbel

oded.arbel@greenfieldtech.net mailto:oded.arbel@greenfieldtech.net Greenfield Tech http://greenfieldtech.net/

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