Push to talk
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Push to talk, commonly abbreviated as PTT, is a method of conversing on half-duplex communication lines, including two-way radio, by pushing a button in order to send, allowing voice communication to be transmitted from you, and releasing to let voice communication be received.
The term has come to be more commonly known as referring to a feature that is available on certain more recent 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 (in a fashion similar to the "trunking" feature of newer commercial and public-safety two-way radios). 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 in order to talk to one another. PTT commonly does not use up the regular airtime minutes that are available for general voice calls, but uses up a certain amount of special minutes that are used specifically for push to talk calls, or depending on one's billing plan, may be flat-rated.
Nextel Communications introduced mobile push to talk several years ago and is currently the leader in this industry. Nextel's preferred iDEN technology is also used by SouthernLinc in the southeastern US, and several other carriers. Recently, Verizon Wireless and Sprint PCS in the United States, Advanced Info Service (AIS) in Thailand, Telstra in Australia and also Bell Mobility (known as 10-4 service) (CDMA) and Telus Mobility (known as MIKE) (iDEN) in Canada 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. 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 AG, AT&T Wireless, and Cingular Wireless with the aim of creating a commercial offering enabling inter-operability between vendors.de:push-to-talk es:PTT