Push to talk
Push to talk, commonly abbreviated as PTT, is a method of conversing on half-duplex communication lines, by pushing a button in order to send, allowing voice communication to be transmitted from you, and releasing to let voice communication be received.
PTT is a feature that is available on certain mobile phone models.
It allows the mobile phone, when in a special mode, to function as a digital two-way radio in push-to-talk operation. Only one person at a time can talk, by pressing a PTT button, and one or several others can listen instantly. The service connects mobile phone users with each other within seconds. Currently, PTT users have to belong to the same mobile operator's (carrier's) network.
PTT does not use up the regular airtime minutes that are used for general voice calls, but uses up a certain amount of special minutes that are used specifically for push to talk calls.
Nextel Communications introduced mobile push to talk several years ago and is currently the leader of this industry.
Recently, Verizon Wireless and Sprint PCS in the United States, Advanced Info Service (AIS) in Thailand, and Telstra in Australia launched their push to talk services. And more operators all over the world have announced intentions to launch similar services.
Verizon is using for its service the Motorola v60p mobile phone, a modified version of the v60 that has the push to talk feature and has been adapted to use the CDMA network instead of the iDEN network. Sprint PCS is using several models of Sanyo phones equipped with similar technology.
Telstra and AIS are using the Nokia 5140 mobile phone and their GPRS networks.
The Motorola and Nokia versions of PTT are based on 2.5G packet-switched networks (CDMA by Motorola, GPRS by Nokia) and use SIP and RTP protocols. These particular versions of PTT are called "Push to Talk over Cellular", which is abbreviated "PoC".
The Open Mobile Alliance is defining PoC as part of the IMS - IP Multimedia System - framework, and the standard is expected to be finalized in late 2004.
A pre-standard version of PoC is also defined by the industry consortium made up of Motorola, Nokia, Ericsson, Siemens, AT&T Wireless, and Cingular Wireless with the aim of creating a commercial offering enabling inter-operability between vendors.
