As I understood Anuran is after the SIP retransmission timer.
From the description, I think the first INVITE, which I assume triggers the pushkit voip to IOS stuff, is missed, then (with default timer T1) after 500ms the first retransmission is done, then after another 500ms you get the 2nd, then after 1s the 3rd, after 2s the 4th, after 4s the 5th, after 8s the 6th and finally after 16s the 7th. This is probably why if you wait 10/15s it works, because probably the 5th or 6th retransmission hits your client. If you wait just 5s you can fall under one window without retransmission (if you miss the 5th you have to wait 8s for the next retransmission).
You can change the timer T1 in the TM module and hope the retransmissions do the job for you. It might work but doesn't look safe to me. I have no idea how this pushkit voip event works, but you may have problems of NAT ports being closed due to lack of SIP activity, then the INVITE will never reach your destination anyway.
The way to go seems what David has suggested about suspending the Invite transaction while your client start-up and register, but I don't know details about this....

Cheers,
Patrick Wakano



On Wed, 18 Dec 2019 at 07:34, Henning Westerholt <hw@skalatan.de> wrote:

As mentioned, it is more a User agent related topic. But there is a module that provide related functions in Kamailio:

https://kamailio.org/docs/modules/stable/modules/sst.html

Cheers,

Henning


Am 17.12.19 um 19:51 schrieb Anuran Barman:
Thanks for the reply. Sharing doc links of Session timer settings related to Kamailio specifically will be greatly appreciated.

On Wed, 18 Dec 2019 at 12:18 AM, Yuriy Gorlichenko <ovoshlook@gmail.com> wrote:
Session-Expires header ( Just remembered right name) will help you
See rfc 4028

On Tue, 17 Dec 2019, 19:44 Yuriy Gorlichenko, <ovoshlook@gmail.com> wrote:
Hi. It is no a kamailio question but sip question itself. You can manage how often te invite will be by using session-timers. It will help you to setup time range between reInvite ir whatever message you will use as keepalive

On Tue, 17 Dec 2019, 19:34 Anuran Barman, <anuranbarman@gmail.com> wrote:
Hi, I am using Kamailio for my SIP Phone app. My main SIP client is the iOS app. Till now everything is working fine regarding the calling. But the problem is when the app is killed I am not able to pick up incoming call. The thing is, when app is killed I am sending PushKit VOIP message to my ios app to wake it up. App is waking up. But by the time app is waking up, the original INVITE message got missed up. So according to SIP protocol it will re-INVITE after some time. Currently if I keep my app open for 10-15 secs after it wakes up, I am able to get the re-INVITE and everything works fine just as it was supposed to. But waiting 10-15 sec on the app is not practical in any sense.

So my question is there any way I can reduce the re-INVITE time to like 5/6 seconds so that as soon as the app open it will wait for 5/6 seconds (practical upto some extent) and it will get the call ? Or what kamailio is using as the interval time is a SIP standard and can not be changed? If possible to do so, how can I do that? Please help.
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