IMS-based push-to-talk over GPRS/UMTS

This paper reports the design of a push-to-talk service operated over a GPRS/UMTS network (push-to-talk over cellular - PoC). The new service was built based on the 3GPP IP multimedia subsystem (IMS). We discuss the key design decisions made for our solution and describe how the IMS supports the new service. The contributions of this paper are: [1] the verification of the overall PoC approach through an implementation; [2] a discussion of design details that were not defined in the original PoC specifications; and [3] the measurement results achieved in a live network based on existing GPRS access technology.