Hello Benoit,
we are experiencing some strange issues with mikrotik NAT + SIP.
Sometimes we see that SIP is no more working, no audio on both sides.
Rebooting the router solves the issue.
Not sure what's happening in the mikrotik NAT, just thinking to reboot
it every night :(
Regards
Paolo
Hello fellow Routerosers!
At a customer I came across a strange phenomena.
Sometimes, the customer has 'no audio' situations.
We sniffed for some times and the customer pointed out the calls that
didn't work. And bingo! It looks like there is some issue with port
changes.
Here is a description of the SIP dialogue which causes tie issue:
Dialoge between IPA:5060 and IPB:5060
IPA is a mikrotik (6.37.3) doing NAT and SIP ALG enabled for port 5060
PBX behind mikrotik has SIP ALG disabled.
IPB is the VoIP Provider Voice Switch.
IPC ist a DSP Board of that Provider.
* IPA Invite (RTP at IPA:5008) => IPB
* IPB 183 Progress (RTP at IPC:25001) => IPA
IPC:25001 is sending RTP to IPA:5008
IPA:5008 is sendint RTP to IPC:25001
Caller (IPA) is hearing early audio (ringback tone).
Captured data shows that audio is also being transmitted from IPA to
IPC but that has no use as the caller has not yet picket up.
Caller Picks up the phone.
* IPB 200 OK (RTP at IPC:25001) => IPA
* IPA Ack => IPB
IPC:25001 is sending RTP to IPA:5008
IPA:1024 is sending RTP to IPC:25001
Well IPA has changed port, but to my understanding on how SIP works
this should not cause an issue, because only the receiving port does
matter.
Listinging to the caputred RTP streams shows, that there is audio
flowing in both directions.
Still both sides report, they cannot hear each other.
If the 183 and 200 contain the same port, everything is fine. That port
change does not happen in most cases.
So I wonder, is the NAT code of the mikrotik sometimes change that port?
Is there anything in the SIP RFC's that forbids such a sending port
change?
-Benoît Panizzon-
--
Ing. Paolo Di Francesco
Level7 s.r.l. unipersonale
Sede operativa: Largo Montalto, 5 - 90144 Palermo
C.F. e P.IVA 05940050825
Fax : +39-091-8772072
assistenza: (+39) 091-8776432
web: http://www.level7.it
_______________________________________________
Mikrotik mailing list
Mikrotik@mail.butchevans.com
http://mail.butchevans.com/mailman/listinfo/mikrotik
Visit http://blog.butchevans.com/ for tutorials related to Mikrotik RouterOS
