On 6 Jul 2009, at 19:47, Alex Hermann wrote: > On Thursday 02 July 2009 12:33:14 Dan Pascu wrote: >> Another false assumption is that the receiving endpoint would >> accept a >> media stream coming from a source that was not negotiated in the >> current session. > > How is the source IP:port negotiated in SDP? > > AFAIK only the destination IP:port is negotiated, an UA only > specifies the > address is it willing to _receive_ RTP on.
The RTP stream contains both a sequence number and a signature. The signature is the same for the life of the stream, while the sequence number is incremented with each packet. The destination may choose to learn the signature from the first packet and discard any packet not having the same signature, so a newly negotiated RTP stream outside of the dialog will fail. It will also ignore any packet with a sequence number that is lower than the last sequence number, because it thinks it already did process that chunk. The destination may even employ security measures similar to mediaproxy: it can learn the IP address from the 1st packet and refuse any packet from a different IP until the stream is renegotiated using a re-INVITE. Overall, all these issues do not exist if the MOH is delivered through a stream negotiated inside the same dialog using a re-INVITE, but they pose a problem if the MOH comes via a stream from a different dialog. It's lottery: it may work with some particular devices, it may not with others. -- Dan _______________________________________________ Users mailing list [email protected] http://lists.opensips.org/cgi-bin/mailman/listinfo/users
