I have been using ethereal/ wireshark network protocol analyser on GNU/ Linux for over last 3 years, for trouble shooting, for a subject that I am teaching, for analysing protocols, to study network behaviours and also for my research work. Highly recommended if you are anyway involved with computer networks of any type.
So the developer in you has captured the packets using ethereal/ wireshark and now need to perform some macho custom analysis of the captured data, that may not be possible or too cumbersome using wireshark. Here is my own experience with that and hope it helps you save some time.