PTT over IP: what it is and how it works

PTT over IP is a push-to-talk radio call carried over an internet connection, usually the mobile phone networks, instead of a radio frequency. You press a button, speak, and everyone in your group hears you, just as on a two-way radio, except that the range is wherever there is mobile coverage and the groups are set up on a server rather than programmed into each handset.

Summary: PTT over IP turns a radio call into data. The handset sends your voice over the mobile network to a server, and the server passes it to everyone else in the group. There is no radio licence to apply for and no radio equipment to put up at your sites.

You will also see it called push to talk over IP or PoC. What it costs and how teams buy it is on our page about Push-to-Talk over Cellular; this article covers how it works and how it compares with the radios you may already have.

How PTT over IP works

The handset is either a dedicated radio with a push-to-talk button and a SIM card inside, or a phone running an app that does the same job. When you press the button, it records your voice, squeezes it into small packets of data and sends them over its connection. On a radio that is almost always the mobile phone network, though some handsets can also use Wi-Fi inside a building.

The server is where the group lives. It knows who belongs to each group and who is online. When your audio arrives, it passes it on to every other member who is connected, and their handsets play it. When you let go, the group is free and the next person can reply. Only one person holds the floor at a time, so the etiquette of a radio channel carries over unchanged.

That is the whole trick. The radio waves only travel between each handset and its nearest phone mast. Everything after that is ordinary internet traffic, which is why two people a hundred miles apart can share a group as easily as two people in the same car park. A control room can join the same groups from a computer and usually see where each handset last reported its position.

What you need to use it

Each handset needs a SIM with a data allowance. Push-to-talk voice uses little data compared with a video call, so the plan can be small, but it needs coverage where your people work.

The handset can be a dedicated PoC radio, which looks and feels like a two-way radio with a proper button and a loud speaker, or the app on a phone the user already carries. Many teams mix the two, with radios for frontline staff and the app for managers.

Finally you need an account on a push-to-talk service. An administrator adds each person, decides which groups they belong to and approves their handset. From then on, changes are made centrally and reach the handsets over the air.

How it compares with conventional two-way radio

Conventional radio sends your voice over a radio frequency, from handset to handset or through a repeater. PTT over IP sends it as data over the phone networks, and that one difference explains most of what follows. For the fuller side by side view, including cost and day to day use, see how PoC compares with traditional two-way radio.

Range. A conventional handset reaches as far as its signal carries, which depends on its power and on what is in the way, and going further means installing repeaters or base stations. A PTT over IP handset reaches anyone in the group who has a connection, so a team spread across several towns stays on one channel.

Licensing. Ofcom's Business Radio guidance says that using a radio system requires a licence from Ofcom, either a Light licence with a set list of frequencies or a Technically Assigned or Area Defined licence coordinated for a particular site or area. PMR446 handsets are the exception, listed by Ofcom among its licence-exempt devices for use over short distances. PTT over IP handsets transmit on the mobile networks, whose spectrum Ofcom licenses to the network operators, so there is no Business Radio licence for the user to apply for.

Hardware. Conventional radio means handsets that suit your frequencies, plus any repeaters or base stations the range demands. Here the handset and the SIM are the whole kit, with nothing to mount on a roof.

Group management. On a conventional fleet, channels are usually programmed into each radio with a cable and software, so a change means collecting the handsets. With PoC the groups sit on the server. Moving someone to a new site's group, or creating a group for a single job, takes a few clicks and applies straight away.

What it is good at

It suits teams who are spread out. Mobile patrols and staff covering several sites get one conversation without anyone planning repeaters for it. It also suits organisations that change shape often, because a new contract or a temporary site is handled by adding users and groups, with no reprogramming and no new licence.

Questions buyers usually ask

Does it work indoors? It works wherever the handset has a usable connection, which in most buildings is the mobile network and in some is the building's Wi-Fi. Basements and heavily shielded buildings are the places to check, as they are for any radio system, and the sensible approach is to try handsets at your own sites on a normal shift.

What happens when there is no signal? A handset with no connection cannot send or receive a call until it gets one back. A well designed system makes that obvious to the user, rejoins their group automatically when the signal returns, and shows the control room where the user was last seen. Teams who work in known dead spots can agree to check in before going down and again on the way out.

Is there a delay? There is a short pause between pressing the button and being heard, because the voice goes via a server. Users soon fall into the habit of pressing, waiting a moment, then speaking, which many radio users already do.

Where RevoNet fits

RevoNet is a PTT over IP system built for UK teams who want a proper radio. The RevoNet Handheld is a dedicated push-to-talk radio with RevoSIM connectivity, designed to reduce dependence on a single UK mobile operator. Your groups and radios are managed from the RevoNet control room in a web browser, and your team presses the button and talks, across the UK, without a radio system to install.

Read more about Push-to-Talk over Cellular with RevoNet, see the RevoNet radios, or request trial radios and try it on a real shift with your own team.

Frequently asked questions

What is PTT over IP?

PTT over IP is push-to-talk radio carried over an internet connection instead of a radio frequency. You press a button and speak, and a server passes your voice to everyone in your group over the mobile networks, so the range is wherever there is mobile coverage.

Is PTT over IP the same as PoC?

Very nearly. PoC, or push to talk over cellular, is PTT over IP where the connection is the mobile phone network. PTT over IP is the broader term and can also cover Wi-Fi or a wired connection, but for radios used out on the ground the two names mean the same thing.

Do PTT over IP radios need a licence?

No Ofcom radio licence is needed, because the handsets use the mobile networks, whose spectrum is already licensed to the network operators. Conventional business radio systems usually do need an Ofcom Business Radio licence.

Can PTT over IP radios talk to our existing two-way radios?

Not directly, because conventional radios talk over a radio frequency and PTT over IP radios talk over the phone networks. Many organisations run both side by side for a while and move over one site at a time.

Sources

• Ofcom: Business Radio (licence requirement and licence types)
• Ofcom: Licence-exempt devices (PMR446)
• Ofcom: Review of Ofcom's market-based approach to mobile spectrum management (mobile network operators' spectrum licences)