how to determine the protocol in a packet ?

drife
Joined: Thu 21 of May, 2009

how to determine the protocol in a packet ?

Posted:Thu 21 of May, 2009 (13:25 UTC)
Hello everybody,

I'm trying to develop a program to calculate the delay in a VoIP
conversation, using the RTCP packet.

The problem is, I can't filter on the RTCP packet with jpcap, I must
take the UDP one. I don't know how to recognize a RTCP packet. I've
studied the RTCP protocol with the RFC and wireshark, but I didn't
find any way the know the protocol in the UDP packet.

How wireshark can "guess" the protocol inside the UDP packet ?
Can somebody help me ?

thanks in advance, sorry for my bad english.

Regards.