Hi Richard, thanks for the response. When A call B. The INVITE message will go through SIP server. And this SIP server can modify the media address in SDP.
When both A, B use STUN. The INVITE message SDP contains the media address A obtained through STUN, and SIP server does not modify it. So that B will then send rtp packet to this address, hence cause no voice But when either A or B use STUN. This SIP server modify the the media address to the address of RTP server. This case A can hear B and vice versa Why is that ? On Thu, Feb 28, 2013 at 8:59 PM, Richard Barnes <[email protected]> wrote: > Hi Khoa, > > > Hi, I have Kamailio as SIP server and RTP server. Client is PJSIP. > > > > I read that STUN is for non-symmetric NAT, and RTP server is for > symmetric > > NAT. > > You are correct that an "RTP server" (also called a "TURN server") is > usually necessary in the case of symmetric NAT. For some illustrations, > see this slide deck: > <http://www.viagenie.ca/publications/2008-09-24-astricon-stun-turn-ice.pdf > > > > Your client will have to gather TURN candidates and send them to the other > side during ICE negotiation. > > > > Supposed A calls B. > > > > If A, B both use symmetric NAT and STUN, they cannot hear each other > > In this case, if you only use STUN, media will fail. (I assume "they > cannot hear each other" means RTP isn't going end to end.) You need to use > an RTP server (== TURN server). > > > > If A or B use non-symmetric NAT and NOT using STUN, they cannot hear each > > other. > > In the case of non-symmetric NAT, you still need to use STUN. NOT using > STUN will only work if there are no NATs. > > > > I read > http://tools.ietf.org/id/draft-takeda-symmetric-nat-traversal-00.txt > > for Prediction Failure, is that related to this problem ? > > That is a very old document, and does not look technically sound. In > particular, predicting next port numbers will usually not work, because > NATs can assign port numbers in any order they want. I would start with > the ICE RFC, and work from there: > <http://tools.ietf.org/html/rfc5245> > > Good luck! > > --Richard -- Khoa Pham HCMC University of Science Faculty of Information Technology _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
