Current Use in Mobile Telephony (PoC)
Full-duplex operation on mobile phone networks is made possible by separate frequencies for transmission and reception. Mobile Push-to-Talk service, offered by some mobile carriers, adds functionality for individual half-duplex transmissions to be sent to another party on the system without needing an existing connection. Since the system is half-duplex, only one user can transmit by PTT at a time; the other party is unable to transmit until the transmitting user unkeys his PTT button. Now, PTT service is not only supported between parties on the same mobile carrier service, users with different carriers will be able to transmit to each other by PTT.
In addition to mobile handsets, the Push-to-Talk service may be complemented with fixed PC applications acting as PTT clients connected to the mobile operator via secured Internet links. A dispatcher is a specialized type of PC Client but designed for heavy load dispatching, i.e. coordinating many issues typically caused when managing large fleets from a dispatch center. In Spain, Telefonica has launched PTT offering with focus on dispatch orientated group communications.
Nextel Communications introduced mobile push-to-talk in August 1993 using iDEN. The first system was turned on in Los Angeles with 134 sites and a capacity for 50,000 dispatch subscribers. The "MOTO Talk" feature by Nextel includes both on- and off-iDEN network walkie-talkie service for newer Motorola phone models. The off-iDEN-network handset-to-handset Direct-Talk feature works for a radius of up to six miles.
Verizon Wireless enabled push-to-talk communication on its BlackBerry devices in March 2010, requiring download and a monthly fee.
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. There are few full-fledged commercial deployments of OMA PoC. It is very unclear whether OMA PoC will be seriously launched in the European market.
A pre-standard version of PoC is also defined by the industry consortium made up of Motorola, Nokia, Ericsson, Siemens AG and AT&T Mobility with the aim of creating a commercial offering enabling interoperability between vendors.
As of June 2010, no tier-1 operator worldwide has launched OMA. The availability of OMA handsets and fully inter-operable solutions remains to be seen. OMA solutions are missing the most important factor for such a niche market, which is performance. In addition, the standard was mainly adopted by NSN, Nokia, Ericsson and others, none of whom have had major success or background in PTT. OMA PoC also assumed it is a service for consumers, which is not true -- PTT/PoC is an enterprise service. On the bottom line, it is more of a North American phenomenon due to existence of iDEN and other networks. Other parts of the world do not know the service and operators are having a hard time identifying who needs this service.
Read more about this topic: Push-to-talk
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