Ethereal-users: Re: [Ethereal-users] how does ethereal determine whether RTP or not?

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From: Guy Harris <guy@xxxxxxxxxxxx>
Date: Thu, 4 Sep 2003 11:47:36 -0700

On Thursday, September 4, 2003, at 4:56 AM, darren wrote:


I did some capture of a Video stream with ethereal on my own
computer...after which ethereal correctly identified the UDP packets as
being RTP.

After I did a filter on all the RTP packets (filter RTP) and save the
filtered packets in a separate file, I reopened the file in another ethereal 
session...but this time...it was identified as simply UDP...
The packets you filtered out probably contained H.245 or RTSP traffic that specified that RTP would be used in future UDP traffic between particular IP addresses and ports; without that traffic, Ethereal doesn't know that the random UDP ports in question happen to be carrying RTP traffic.