Everything about Push To Talk totally explained
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.
Conventional two-way radios
For commercial,
family and
amateur two-way radios, the PTT or pressel is a switch that's 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's 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's provided over a
cellular phone network. A typical Push to Talk connection connects almost instantly. 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 doesn't 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 doesn't 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 handset-to-handset
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. 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.
Current use in military communications - Command and Control Push To Talk (PTT)
The essence of a PTT system in theatre is the ability to deliver an open conference where everyone can talk and everyone can listen: everyone at HQ, the field command centres and in rapid response units. Where users require voice communications that are instant, reliable and of the highest quality. PTT solutions such as the one offered by Speakerbus’ enable defence services the unique combination of modular communications platforms with the flexibility to provide instant, open audio or audio communications over a variety of networks including IP, PSTN, SATCOM and UHF/Microwave/Wi-Fi radio’s.
Operators using PoC
Several
operators are using a Push To Talk server in their
GSM /
GPRS /
EDGE /
CDMA /
UMTS networks. Most operators, if not all, offer this service as a separate charge that don't 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's 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 together with emphasis on a
dispatcher equipment. The
dispatcher (AKA "Terminal de Despacho"), is a PC with a
PTT dispatcher software.
In UK, Push To Talk UK Ltd launched its
YouPoC Service
, specifically aimed at helping businesses and enterprises get the most out of wide area one to many communications.
Also,
Palringo provides a novel Mobile Instant Messaging client for mobile phones and PCs. Palringo allows you to instantly exchange text, photos, and vocal IMs with groups or individuals.
Service providers by region
Further Information
Get more info on 'Push To Talk'.
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