A Hybrid Extension for IP Multicasting in Push-to-talk over Cellular Systems

OMA Push-to-talk over Cellular (abbr. PoC or PTT) as an IP-based service can be considered the first Voice-over-IP technology delivered in a broad manner in cellular networks world wide. Two key differences between PoC and regular voice communication systems are its half-duplex nature, which converts it into 'walkie-talkie' style of service and ability to establish group sessions between large groups of participants. As a matter of fact, majority of available PoC solutions are inefficient in handling groups of large size because they rely on IP unicasting for delivering media streams. This introduces not only redundancy and greater packet loss, but also increases computational and transmission effort. This paper proposes a hybrid IP multicasting extension for Push-to-talk technology allowing to reduce group size limitation significantly and increase the performance of large scale Push-to-talk systems. The proposed enhancement is elaborated and verified basing on an automatic testing framework feedback and some statistical measurements.