Push to talk

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Template:Table Mobile phone standards Push to talk (PTT) is a method of conversing on half-duplex communication lines, including two-way radio, using a button to switch from voice transmission mode to voice reception mode.

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Early Use in Mobile Telephony

One of the earliest mobile telephone protocols used PTT. It was the mobile equivalent of operator-assisted land telephone service. The protocol was as follows: The mobile telephone user pressed and held their PTT (Push-to-Talk) button for several seconds to get the mobile operator's attention. When they released PTT, an operator would reply (transmit on their channel) and ask them the number they wanted. The user would key up (PTT) and tell the operator the number they wished. The operator would dial and connect the land line, and the conversation would proceed. When there was no activity for a while or the land line hung up, the operator could reuse the channel. This was used at least into the 1980's in Canada. This was replaced by MTS.

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Current Use in Mobile Telephony

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. The evolution of the standards will make such interconnection possible in the near future.

When used in GSM networks, the PTT service commonly does not use up the regular airtime minutes that are available for general voice calls.

Nextel Communications, now merged with Sprint, introduced mobile push to talk several years ago using iDEN and is currently the leader in this industry. The "MOTO Talk" feature by Nextel affectionately called 'Beep-beep' or 'chirp' by teenagers includes both on and off iDEN network walkie-talkie service for newer Motorola phone models. The off iDEN-network headset-to-headset 'Direct-connect' feature works for a radius of upto 6 miles.

The Motorola, Nokia, Ericsson, Siemens, Sonim, Huawei, Mobile Tornado, Wireless ZT, etc. versions of PTT are based on 2.5G or 3G packet-switched networks 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 IP Multimedia Subsystem, and a first version of OMA PoC standard was finalized in first half of 2005.

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 (ATTWS and Cingular merged in September 2004) with the aim of creating a commercial offering enabling inter-operability between vendors.

Several operators are using Pre-Standard Push To Talk Server in GSM / GPRS / EDGE / CDMA / UMTS networks.

Terminal vendors has several variations of software installed on mobile terminals, so there is no 100% compatibility list available.

In Japan, NTT DoCoMo implemented Push-to-Talk in late 2005 with the introduction of new FOMA 902i series handsets. It's billed at 5 yen per push, and has an "unlimited" option for 1000 yen/month.

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Some operators providing Push To Talk services

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Manufacturers of PTT mobile phones

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See also

de:Push-to-talk es:Push to talk ja:プッシュ・ツー・トーク tr:Push to talk

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