Abstract: To solve the problem that transfer multi-data like images, videos in digital trunked communication system, the air interface protocol stack of digital trunked is analyzed deeply, and the sub-network dependent convergence protocol (SNDCP), which is the provider of packet data service, is researched. Then, the dependent function model of the protocol is designed and coded based on model design. In developing, IBM Rational Rhapsody which is a develop tool based on UML is used to make the develop program easy and clear. At last, parameters and sequence of the protocol are proved to be compliance with the protocol standard of digital trunked communication system by making conformance tests to the protocol.

Key words: digital trunked, model design, protocol stack, packet data, sub-network dependent convergence protocol