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- -- I m p r o W a r e A G - Leiter Commerce Kunden ______________________________________________________ Zurlindenstrasse 29 Tel +41 61 826 93 00 CH-4133 Pratteln Fax +41 61 826 93 01 Schweiz Web http://www.imp.ch ______________________________________________________ _______________________________________________ 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
