RTCP port number

Mohamed Mustafa M.Mustafa at SDXPLC.COM
Thu Oct 21 11:05:11 EDT 1999


Hi Everyone,

Annex A of recommendation H.225.0 states that  "RTP uses an even port number
and the corresponding RTCP stream uses the next higher (odd) port number".

Can anyone clarify what the RTCP port number should be if an endpoint uses
two different RTP port numbers (one for transmitting and one for receiving).

To avoid confusion, I'll describe the specific scenario I'm trying to
resolve;

Following completion of the H.245 capability exchange and master/slave
determination, the following messages are exchanged to establish a pair of
unidirectional media streams between the two endpoints.

        1). A transmits an OpenLogicalChannel request to B specifying the
port number (a1)
        that it will use to transmit the RTP packets

        2). B transmits an OpenLogicalChannel request to A specifying the
port number (b1)
        that it will use to transmit the RTP packets

        3). B transmits an OpenLogicalChannelAck response to A specifying
the port number (b2)
        which the RTP packets should be transmitted to

        4). A transmits an OpenLogicalChannelAck response to B specifying
the port number (a2)
        which the RTP packets should be transmitted to

Normally, a1 and a2 are the same so there is no confusion as to A's RTCP
port number. However, the Phone Dialer application that comes with Windows
2000 does not use the same port numbers in the OLC and the OLCA messages.


Thanks,

Mohamed
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