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Push to talk

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Mobile communication standards
GSM / UMTS (3GPP) Family
2G GSM GPRS EDGE (EGPRS) EDGE Evolution HSCSD
3G UMTS (3GSM) HSPA HSDPA HSUPA HSPA+ UMTS-TDD TD-CDMA TD-SCDMA FOMA
Pre-4G UMTS Revision 8 LTE HSOPA (Super 3G)
cdmaOne / CDMA2000 (3GPP2) Family
2G cdmaOne
3G CDMA2000 EV-DO
Pre-4G UMB
Widely Used Other Technologies
1G AMPS
2G D-AMPS
Other Technologies
0G PTT MTS IMTS AMTS OLT MTD Autotel / PALM ARP
1G NMT TACS / ETACS Hicap CDPD Mobitex DataTAC
2G iDEN PDC CSD PHS WiDEN
Pre-4G iBurst HIPERMAN WiMAX WiBro (Mobile WiMAX) GAN (UMA)
Frequency bands SMR Cellular PCS

Push-to-talk (PTT), also known as Press-to-Transmit, is a method of conversing on half-duplex communication lines, including two-way radio, using a momentary button to switch from voice reception mode to transmit mode.

1 Conventional two-way radios
2 Current use in mobile telephony (PTT PoC)
- 2.1 Operators using PoC
  - 2.1.1 Service providers by region
3 See also
4 References

Conventional two-way radios

For commercial, family and amateur two-way radios, PTT is a button that is pressed when needing to transmit with the radio on the tuned frequency or channel. While the PTT button remains unpressed (or unkeyed), any radio traffic that is received on the selected channel or frequency is heard through the radio's speaker. Unless the radio supports full-duplex operation, received audio is usually muted while the PTT button is pressed. Simultaneous full-duplex transmission and reception on a radio is generally not supported unless either the transmit and receive frequencies have significant separation between the two frequencies, or two different antennas are used with enough distance between them, or a cavity filter is used, due to an effect known as desensing which cancels out received transmissions. More recently, the PTT concept has been adopted by cellphone carriers as a way to instantaneously send transmissions to other users on the system, emulating walkie-talkie communications on a mobile phone network.

Current use in mobile telephony (PTT PoC)

PTT PoC or Push to Talk over Cellular is a feature similar to walkie-talkie that is provided over a cellular phone network. A Push to talk connection is typically connected virtually instantaneously. One significant advantage of PoC is allowing a single person to reach an active talk group at a button press, thus users no longer need to make several calls to coordinate with a group. Push-to-talk calls are half duplex communications — while one person speaks, the other(s) listen(s). 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. Such a system does not allow for casual transmissions to be sent to other parties on the network without first dialing them up, like is allowed on two-way radios. 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 (utilizing a single frequency), 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. However, the advancement of this service will likely bring interconnectivity of PTT traffic between different networks in the near future. 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 in the dispatcher. 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 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 (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-Talk feature works for a radius of up to six miles. Sprint plans on implementing Qualcomm's QChat on their EV-DO Revision A network. QChat has connection times of less than a second, which brings it in line with Nextel's MOTO Talk connection speeds. This will in time replace their ReadyLink Push-to-Talk technology. The Mobile Tornado, Motorola, Nokia, Ericsson, Siemens, Sonim, Wireless ZT, Clarity, 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. Full fledged commercial deployments of OMA PoC are few and in between. 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.

Operators using PoC

Several operators are using Pre-Standard Push To Talk Server in GSM / GPRS / EDGE / CDMA / UMTS networks. Most operators, if not all, offer this service as a separate charge that do not use normal voice minutes. The service offering defined by the operators varies depending on the market segment which they address. When addressed to consumers or small corporates, the service is only accessible from PTT enabled mobile phones. However, when addressed to medium and big corporations it may include PCs with simple PoC applications installed in it, or more advanced PC software such as dispatchers. Terminal vendors has several variations of software installed on mobile terminals, so there is no 100% compatibility list available. In Germany, Talk-IP Ltd. offeres Mobile Tornado's PTT solution as managed service for enterprises. 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, Verizon Wireless offers PTT service using the Motorola PTT solution, AT&T Mobility, Alltel 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 Mobility (Mike), Bell Mobility and Aliant Mobility (Bell 10-4). Both Bell and Aliant offer the service which allows customers to use the service in the United States without roaming charges. The service allows a caller to simultaneously 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. In Slovakia, Ardaco developed SecurePTT solution for information and communication security area. In Spain, Movistar (Telefonica) launched in October 2007 the PTT service targeted to the professional market for heavy duty usage. Its professional PTT service is build up of rugged Sonim XP1 and Nokia handsets toghether with emphasis on a dispatcher equipment. The dispatcher (AKA "Terminal de Despacho"), is a PC with a PTT dispatcher software.