Matti Zemack schrieb: > Hi all, > > > I have a few question regarding how Pjsip and Pjsua goes about deciding > what port to send it's packets to. > > Using Wireshark I've noticed the following in setting up a connection > between Pjsua (with --rtp-port set to 5004) and some other SIP > implementation; > > 1. The call is set up without any SIP server, and both parties describe > that they will be sending to port 5004 (in the SDP). The SDP describes where the clients will receive RTP (not where they will send to) > 2. Pjsua is sending it's packets to the receivers port 5004 as described > in in the SDP setup & the other SIP implementation sends it's packets to > port 5004 of the Pjsua. Here it should be noted that the other SIP > implementation's source port is xxxx. This is called a-symmetrical RTP (different port for sending and receiving) in contrast to symmetrical RTP where the client uses the same port for sending and receiving. Note: A client behind NAT only works if it has symmetrical RTP and symmetrical SIP signaling. > 3. The other SIP implementation sends a few ICMP saying that port 5004 > is unreachable. Then the other client is wrong. If the client announces port 5004 it should receive packets on pot 5004 (maybe there is a NAT/PAT which changes ports?) > 4. Pjsua suddenly without any previous SDP message changes it's > destination port to xxxx. > > During the whole session the audio going from the other SIP > implementation to Pjsua is fine. The other SIP implementation never > receives audio as it is awaiting audio on port 5004, but all output from > the Pjsua is going to xxxx. But pjsua tried to send to port 5004 before and the client responded with ICMP errors, thus sending to 5004 wont work too. > > So my questions are; > A. Does Pjsua switch its destination port to xxxx because of the ICMP's > or is this switch done because Pjsua always wants to send it's packets > to the source of the received packets, which would be needed going > through NAT's? benny? regards klaus > B. If this is how Pjsua smartly tries going through NAT's. Does there > exist a setting for Pjsua in run-time, start-up flag or at compilation > time where this functionality can be switched off? > > > Thanks in advance, > Matti Zemack, BBC R&I, Kingswood Warren, UK > > > http://www.bbc.co.uk > This e-mail (and any attachments) is confidential and may contain > personal views which are not the views of the BBC unless specifically > stated. > If you have received it in error, please delete it from your system. > Do not use, copy or disclose the information in any way nor act in > reliance on it and notify the sender immediately. > Please note that the BBC monitors e-mails sent or received. > Further communication will signify your consent to this. > > > ------------------------------------------------------------------------ > > _______________________________________________ > Visit our blog: http://blog.pjsip.org > > pjsip mailing list > pjsip at lists.pjsip.org > http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org
