Push To Talk - PTT

Push-to-talk (abbreviated as PTT or P2T) is a two-way communication method that uses half-duplex mode where transmission occurs in both directions, but not at the same time.

To use PTT, users must press a button on the PTT device while speaking, then release it when done. The listener must then do the same to respond. Common PTT devices include the walkie-talkie. Newer PTT systems use VoIP to provide digital PTT service over 3G data networks. Synonymous with press-to-talk.

PTT PoC or Push to Talk over Cellular is a service option for a cellular phone network which permits subscribers to use their phone as a walkie-talkie. A typical Push to Talk connection connects almost instantly. One significant advantage of PoC is that it allows a single person to reach an active talk group with a single button press; users no longer need to make several calls to coordinate with a group.

Push-to-talk cellular calls are half duplex communications — while one person transmits, the other(s) receive. Traditional mobile phone networks and devices utilize full-duplex communications, allowing customers to call other persons on a mobile or land-line network and be able to simultaneously talk and hear the other party.
Such communications require a connection to be started by dialing a phone number and the other party answering the call, and the connection remains active until either party ends the call or the connection is dropped due to signal loss or a network outage.
Therefore, telephone communication protocol does not allow for casual and immediate transmissions to be sent to other parties on the network. Whereas telephone calls require the lengthy process of dialing, network switching and routing, call setup, and waiting for the other party to answer, a two-way radio has a much quicker protocol because of the immediacy of push to talk communication.

Full-duplex operation on mobile phone networks is made possible by using 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 to be already established.

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 their PTT button. Currently, PTT service is supported only between parties on the same mobile carrier service, and users with different carriers will be unable to transmit to each other by PTT.
In addition to mobile handsets, the Push-to-Talk service might be complemented with fixed PC applications acting as PTT clients connected to the mobile operator via secured Internet links. A specialized type of PC Client is a dispatcher, similar to a PC client but designed for heavy load dispatching.

That is, 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.
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.