A study on session setup for group communications in push-to-talk over cellular using rich presence

The IMS-based, half-duplex push-to-talk over cellular (PoC) service provides a cost-efficient, interactive, and global-reach service for group and individual communications. The media types for PoC users can be voice, video, images, and text messages. Presence service is widely used and is often bundled with PoC and instant messaging (IM) to indicate other users' availability and willingness of communications. In this paper, we investigate the session setup procedure for the PoC group communications within OMA PoC infrastructure and propose a method to optimize the initiation of a PoC prearranged group session using rich presence information. With this method, the SIP signaling traffic and session delay are significantly reduced.

I. Introduction

The modern Push-to-talk technologies have developed from the traditional “Walkie-Talkies” provided by Land Mobile Radio (LMR) network where circuit-switching is typically involved in the calling process. The advent of new technologies, such as Voice over IP(VoIP) and IP Multimedia Subsystem (lMS) [1], have boosted the packet-switching Push-to-talk over Cellular (PoC) available for commercial deployment. PoC is based on a half-duplex communication mode over mobile networks: a user presses a dedicated button and starts to talk after a talk indication is given; while the others listen and have the right to speak only when the floor is idle. A channel is established at the beginning of the call and it is reserved only for the duration of talk spurts due to the nature of the IP technology instead of for an entire call session in a traditional circuit-switching network.