Real-Time Multi-user Transcoding for Push to Talk over Cellular

Transcoding is required to enable interoperability between push to talk over cellular (PoC) clients with incompatible capabilities (e.g. between a PoC client supporting the AMR speech codec and another supporting EVRC). Although the Open Mobile Alliance (OMA) recognizes the need for transcoding in the PoC application, no solution is provided by the standard to enable it. In this paper, we present a transcoding system for real-time multi-user PoC sessions. The solution is centralized at the Controlling PoC Function which manages session control operations and the flow of media streams to enable transcoding to be performed in a distinct transcoding server (TS). There are several advantages to this solution, such as scalability, applicability to all PoC group session scenarios, compatibility with existing PoC specifications, and transparency for existing PoC clients.