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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.

How the technology works

The PTT (Push-to-Talk) service uses a combination of half-duplex and full-duplex signals in order for the service to work. The digital two way radio makes use of the half duplex signal. Full-duplex signals allow both parties to talk at the same time by using two separate frequencies. Full-duplex signals are used when a customer places a traditional cellular call. This technology uses one frequency to send information, and another to receive making the voice call possible. As with all cellular service, both full-duplex and half-duplex signals are actually radio frequencies capable of reaching great distances. The PTT (Push-to-Talk)service uses a half-duplex signal, meaning each call using this service only uses one frequency. This technology is commonly used by dispatchers. To use this service the person placing the call must hold on to button while speaking. While they are holding the button, the party on the other end is unable to speak until the button has been released. This avoids any interruption by the other party. Push-to-talk service currently can only communicate with other users of the service under the same wireless carrier.

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 with GSM and CDMA 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 up to 6 miles.

The Mobile Tornado, Motorola, Nokia, Ericsson, Siemens, Sonim, Huawei, 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.

Currently Cingular Wireless and Alltel offer PTT service using the Kodiak RTX ( Real Time Exchange ) system to deliver PTT speeds comparable to Nextel and SouthernLinc

In Canada the service is provided by several carriers including Telus (Mike), Bell Mobility and Aliant Mobility (10-4). While using the service, customers do not use registered airtime minutes associate with their voice plan. The service is often offered at a discount to those customers who suscribe to a monthly airtime package. Both Bell and Aliant offer the service which allows customers to use the service in the United States without the occurrence of international roaming charges typically associated with cellular use out of country. Customer’s using the service in Canada have the ability to contact users across the country without the occurrence of long distance charges. The service is being promoted as a cost effective method for communication which typically runs a high cost. Offered as a solution to businesses and customer’s who use a great amount of long distance, PTT (Push-to-Talk)service will greatly change the way many consumers do business. The service allows a caller to simoutaniously communicate with multiple users at different locations. By doing so, this eliminates multiple airtime charges associated with three-way calling. With the cellular number portability coming into effect by March 2007, the PTT (Push-to-Talk) service is expected to increase greatly with the removal of Roamer Access Numbers by August 2006. Roamer Access Numbers had given the freedom for customers to not incur incoming long distance charges by answering calls outside their local calling area if the caller first dials the Roamer Access Number.

Some operators providing Push to Talk services

Manufacturers of PTT mobile phones

Manufacturers of PTT infrastructure

See also

Telephony | Instant messaging | Mobile telephony standards

Push to talk | Push-to-talk | Push to talk | プッシュ・ツー・トーク | Push to talk

 

This article is licensed under the GNU Free Documentation License. It uses material from the "Push to talk".

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