Prerequisite - You should be on Sniffer Distributed 4.3 or greater.
Steps -
1. Go into Tools | Protocols Options,
2. Enter port ranges in UDP and / or TCP tabs and associate an intuitive protocol name -like Dce-Rpc.
3. Open the capture file & select Protocol Distribution tab or click Monitor | Protocol Options, if you're monitoring real time traffic
4. Now, when you view the protocol distribution charts, the packets with the TCP / UDP port nos. specified in step 2, should show up under the descriptive name you chose.