Push-to-talk over cellular
In push-to-talk over Cellular ( PTToC , PoC or even PTT shortened) is it is a standard for mobile phones , the quick and easy voice communication for groups in mobile networks describes and after the walkie-talkie function principle.
This service offer enables the customers of the mobile network operators to send a voice message to one or more recipients via the mobile phone with just one touch of a button. The message is not transmitted over a circuit-oriented ( English circuit switched ) cellular connection, but via a packet-switching cellular connection ( GPRS ): The voice message is first divided into data packets and sent to a server . The server forwards the packets to the connected, active clients ( client-server model ). This process explains why the message usually arrives at the recipient with a delay (depending on the reception strength in the cellular network ).
Communication usually takes place in half duplex , which prevents simultaneous speaking and listening. As soon as a client is spoken to, all other clients can only listen. An attempt to speak anyway is prevented by the server. The exception here are the priority calls integrated in some push-to-talk applications as they occur in digital radio systems. This makes it possible to prevent radio messages with lower priority.
The voice quality is similar to that of digital or trunked radio, but thanks to the digital packet transmission it is clearer and easier to understand than with its radio counterparts. Furthermore, with some push-to-talk providers you have the option of listening to voice messages again using a history function.
Technically, the communication works in a similar way to Voice over IP (VoIP). The group members first receive a signal through the SIP protocol, then the voice, so-called “talk bursts” , is transmitted via RTP . There are two reception modes: automatic and manual reception. While with automatic reception the voice message sounds directly from the loudspeaker of the cell phone, with manual reception the user must first press a button in order to hear the first and all subsequent voice messages.
The Open Mobile Alliance (OMA for short) takes care of the standardization . Version 1.0 of the specification appeared in mid-April 2005. Version 2.1 was released in October 2011.
organization
A PoC network is organized like a digital radio network. There are usually one or more groups in which users communicate with one another. A control center often regulates radio traffic and gives instructions to the often mobile clients. The clients can - depending on their internal network access rights - change groups, speak to the group and make individual calls (also to other groups). In different applications it is also possible to send group-internal messages.
Due to the priority settings and the use of the half-duplex method, a certain order is maintained in the radio network.
technology
When T-Mobile was the only network operator in Germany to start offering the push-to-talk service at the end of 2004, PTT could only be used with certain devices. This was mainly due to the fact that the Nokia standard was used and the OMA standard was dispensed with. The Nokia service was preinstalled on the devices, which made it easier for network providers to access. After T-Mobile's PTT service was discontinued on July 1, 2008, there was no network operator in Germany who still offered PTT.
This did not affect the compatibility of the devices, as the services were still in use in Austria (start July 2005) and Switzerland (start 2004) and especially in the USA (since 1999). In addition to Nokia with its own standard, other mobile phone manufacturers such as Motorola or Sony-Ericsson developed PTT-enabled devices.
With the advent of smartphones , push-to-talk was given a new opportunity because the service was easier to install as a mobile app . Above all, one was no longer dependent on the device supporting PTT.
Germany
After push-to-talk had not established itself through the market-leading mobile phone providers in Germany, the marketing of PTT fell back to smaller, private companies. Mobile apps for Android and other smartphone operating systems have been developed that take full advantage of the technical possibilities of mobile phones and, in particular, smartphones. As a result, the user is no longer tied to a network provider, but can use PTT independently of it.
The company TASSTA GmbH supplies a complete communication solution of the same name that uses Push-To-Talk as the basic communication tool. The system was designed for smartphones and, in addition to the pure communication and GPS service, also provides the option of placing orders via geofencing , the use of NFC and QR codes . TASSTA also has a history function that records radio messages and the user can replay them. In addition, handheld radios can be connected via Bluetooth , which makes handling easier for the user. TASSTA is used in the taxi industry , courier and transport services, secret services , utility companies, security services , disposal companies , logistics companies , fire brigades , police and rescue services .
A connection to an existing TETRA or other digital radio network is also possible with TASSTA. Although a lot of data is transported, TASSTA only needs a GPRS connection for the transfer of voice and data packets . TASSTA offers its service, which can also use WLAN , for Android and iOS systems.
Another commercial operator of a push-to-talk (PoC) service is Talk-IP Services GmbH. The use of PTT is made possible across networks via a mobile data connection. The user is therefore not tied to a specific cellular network and the PTT service therefore works in almost all cellular networks worldwide, or alternatively via WLAN. Talk-IP supports mobile phones with the original Nokia PTT function ( S40 ) as well as devices with the Android operating system, Windows Mobile operating system (Pocket PC), Symbian 9 operating system and Windows PCs. Cell phones with GPS receivers can be located by Talk-IP on the PC and can be reached from there depending on the location. In local public transport (ÖPNV) this service is increasingly replacing analog trunked radio. For taxi companies, PTT is "the radio solution with GPS location".
Talk-IP International AG is a commercial supplier for push-to-talk server infrastructures. This company supplies PTT server platforms for service providers, authorities and companies in all leading world languages.
United States
Push-to-talk has long been very popular in the USA, particularly in the trade and with taxi companies. There the service is based on a proprietary trunked radio technology developed by Motorola called iDEN . IDEN is not a PoC solution, as no packet-oriented point-to-point data transmission is used, but a trunked radio technology (see TETRA ). The system-related disadvantages of PoC technology, such as long delays in voice transmission and asynchrony in group connections, do not occur in trunked radio networks (iDEN, TETRA, MPT 1327 ). In particular, the network operator Nextel had great success with its service.
Rest of America
In South and Central America, a large part of mobile communications is now also handled via PTT connections.
Individual evidence
- ↑ OMA releases
- ↑ mobilkom austria: Commercial launch of A1 PUSH TO TALK from mid-July. In: pressetext news agency. June 3, 2005, accessed April 1, 2016 .
- ↑ Orange and Swisscom are introducing Push-to-Talk this year. In: teltarif.de/teltarif.ch. February 23, 2004, accessed April 1, 2016 .
- ↑ TASSTA GmbH
- ↑ Examples of wireless data transfer rates
- ↑ Talk-IP Services GmbH
- ↑ Talk-IP International AG
Web links
- Version 1.0.1 of the specification (PDF; 334 kB)