Hi folks,
Recently, I am confused on the identity of a RTP session.
per RFC3550
RTP session: An association among a set of participants
communicating with RTP. ... A participant distinguishes
multiple RTP sessions by reception of different sessions using
<NOTE>different pairs of destination transport addresses,</NOTE>
where a pair
of transport addresses comprises one network address plus a pair
of ports for RTP and RTCP.
So I draw the conclusion as follows,
a RTP session is identified as a network plus two destination ports(RTP
&& RTCP port).
therefore suppose two SIP UAs taking with each other on unicast UDP.
UA1
UA2
IP: ip1
IP: ip2
RTP port: port1
RTP port: port2
RTCP port: port1+1 RTCP
port: port2+1
so there will be two destination paris (ip1+ (port1,port1+1)),
(ip2+(port2,port2+1))
so based on definition above, this should be thought as two RTP
sessions, shouldn't it?
However, the same section of RFC3550.
<snip>
For example, consider a three-
party conference implemented using unicast UDP with <NOTE>each
participant receiving from the other two on separate port
pairs.</NOTE>
If each participant sends RTCP feedback about data received from
one other participant only back to that participant, then the
conference is composed of three separate point-to-point RTP
sessions.
</snip>
why there're only three RTP sessions, I think it should be six?
since "each participant receiving from the other two on separate port
pairs"
which means each pariticipant should listen on two separate port paris
for incoming RTP packets,
so there're two RTP sessions for each participant, and should be six for
three participants.
Confunsed....
any ideas?
thanks
Regards,
-Rockson
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