A PoC radio works like a two-way radio: you press the key, talk, release it and hear the reply. The difference is the path the voice takes, which runs over the cellular network instead of a radio network. This guide explains how push-to-talk over cellular works, how it differs from traditional radio, and how Respondr puts PoC radios, smartphones and DMR, TETRA and analog networks on the same channels.
What push-to-talk over cellular is
PoC stands for Push-to-talk over Cellular: push-to-talk carried over a mobile network instead of a radio network. Whoever presses the key talks to the whole group, as on a radio channel, and everyone else hears it live without answering a call.
The service has three parts:
- the device, a smartphone, a rugged phone or a PoC radio, with a SIM and a data plan;
- the app, which handles the PTT key, the channels and the audio;
- the server, which receives the voice of whoever is transmitting and delivers it to every member of the channel.
The device reaches the server over 4G or 5G, or over Wi-Fi. That is why push-to-talk over cellular works wherever the device has a data connection, even hundreds of kilometers from the rest of the team.
What a PoC radio is
A PoC radio has the shape and controls of a two-way radio: a side PTT key, a front speaker, often a channel knob and an emergency key. Inside, it is an Android device with a SIM running a push-to-talk app. It does not transmit on a frequency of its own: it uses the mobile operator’s network like any phone.
Next to PoC radios proper there are rugged phones with a dedicated PTT key and Android-based vehicle radios. An ordinary smartphone also becomes a push-to-talk device once you pair it with a Bluetooth PTT button or a speaker microphone.
PoC radio vs traditional radio
A professional radio network (analog VHF/UHF, DMR or TETRA) and a PoC service solve the same problem in different ways.
Coverage. A radio network covers the area served by its repeaters and base stations, and it works where the mobile network does not reach. A PoC radio covers the area where the mobile operator offers data service, with no repeaters to install.
Licensing. A radio network needs whatever licenses its frequencies require. A PoC radio needs no frequency license: it needs a SIM and a data plan.
Infrastructure. The radio network belongs to the organization that uses it, which also maintains it. A PoC service runs on an operator’s network and a server, which can sit in the cloud or on premise.
Functions. A radio network carries voice, the radio ID and some data. A PoC service adds what a connected device can do: GPS position on a map, messages with attachments, private calls, SOS alerts with position.
Neither technology replaces the other everywhere. Many organizations keep their radio network where they need coverage of their own, and use PoC for teams that travel across wide areas or for people who do not need a radio.
How Respondr bridges PoC radios to DMR, TETRA and analog networks
With Respondr you do not have to choose. The existing radio network and the PoC devices share the same channels, through a radio gateway that connects the radio network to IP.
The voice path is simple. When a user on a DMR radio presses the key, the gateway receives the audio and the call signalling and sends them to the Respondr server. The server delivers the voice to every user on that channel: the other radios, the PoC radios, the smartphones and the dispatcher. The reverse path works the same way: the voice of a PoC user reaches the server, the server sends it to the gateway, and the gateway transmits it on the radio network.
The supported gateways cover the most common networks:
- analog networks on VHF and UHF, including marine and aeronautical VHF, through a 4-wire E&M interface;
- DMR networks, Tier I, II and III;
- TETRA networks.
Each network has its own page: DMR dispatch and TETRA dispatch. The radios in the field are neither replaced nor reprogrammed, and they keep working as before.
What a PoC radio does with Respondr
PoC devices run the Respondr mobile app, the same app available for iPhone and Android. On rugged devices the app uses the manufacturer’s own PTT key, so you can transmit with gloves on or with the screen off. Besides voice on the channels, the app offers:
- private calls between two users;
- text messages with attachments;
- GPS position, which the dispatcher sees on the map;
- SOS alerts and man-down detection, with the position attached;
- the dedicated emergency key, on devices that have one.
For fleets managed by an IT department, the app is configured through MDM with Android Enterprise: server and account reach the device with a provisioning token, with no password to type.
Which devices you can use
Respondr runs on iPhone, on Android smartphones, on rugged phones with a PTT key and on Android PoC radios. Accessories include Bluetooth PTT buttons and USB-C speaker microphones. The list of tested models, with the physical key that starts a transmission on each, is on the supported devices page.
If you need to buy PoC radios, DMR and TETRA equipment or accessories, you can find them at dmr-tetra.shop.
The role of the control room
A hybrid network, with radios and PoC devices on the same channels, needs one place to run it from. Respondr’s radio dispatch software shows every channel on one screen, records the transmissions and lets the dispatcher patch two channels from different networks together for the length of an incident. For more on how the work changes in the control room, read why modern dispatch centers are moving beyond traditional radio.
Frequently asked questions
Does a PoC radio work without cellular coverage? No. A PoC radio needs a data connection, from the mobile network or from Wi-Fi. Where the mobile network does not reach, the traditional radio network connected to Respondr through a gateway keeps teams reachable.
Do you need a license to use a PoC radio? No. You need a SIM and a data plan. The radio side of a hybrid system still needs whatever licenses its frequencies require.
Can DMR radios and smartphones share the same channel? Yes. The gateway connects the DMR talkgroup to a Respondr channel, and app users talk and listen on the same channel as the radios.
Does Respondr replace my radio network? No. Respondr connects the radio network you already have to smartphones, PoC radios and the control room. To see how it works with your networks, you can schedule a demo.