VOIP – a brief walkthrough

To change from a traditional radio system to Voice Over Internet Protocol, might sound like a big step. You may question if it is reliable and if the technical solutions are mature enough. Regulations, demand from customers and already made investments in radio traffic solutions might also get in the way of taking the leap. We will in this blog post try to provide a view of the situation today and attempt a prediction of what to come.


There is a big interest in VOIP, and many public transport industry players are talking about it and examining the options. In total, however, only a few operations have taken the leap.

There are a lot of different solutions of VOIP for public transport available. What they have in common is that they need an onboard internet connection, a display, a microphone and speakers. Therefore, with an open Internet connectivity solution and a display already in place in the vehicle, the only additional hardware needed is a microphone and speakers. This is easier and more cost effective than maintaining a traditional radio network.

Why aren’t more operations taking the leap, then? There is a common concern of not being able to reach the bus if relying on VOIP alone, and that is the same concern as private citizens encounter when relying solely on their mobile phones and getting rid of their traditional phone.

In some countries, there could be other issues, like legislation or union regulations that make it difficult to implement VOIP. If the drivers for example aren’t allowed to talk while driving, it causes concerns how to handle the contact with the dispatcher. In that case there might not be a radio connection in use at all, which means that what you compare with is the driver calling from a mobile phone while at a stop. What function does VOIP fill, in this case?

Therefore, a good solution might be to invest in an onboard network solution with a gateway and a display, to connect all onboard systems to one common network first. Then the additional investment to migrate to VOIP is quite small. With the internet connection in place, there is also statistics regarding connectivity, which helps predicting the outcome of migrating to VOIP.

It is then easy to test the VOIP option. Let’s say a certain depot or area has problems with their radio connection, with difficulties to reach the drivers. Then it might be an easier solution to try VOIP, than to expand the radio coverage to solve the problem. If the internet connection and display is already in place, it is in fact easier to install and test the solution in a couple of vehicles than it is to perform a pre study.

The impact of tradition

Since VOIP often replaces traditional radio communication, it usually takes on the same appearance. For example, some operators use hand mic, so that the passengers won’t mistake the VOIP communication for private calls. Push to talk is then used to mimic the radio setup. This means that traditional radio setups might impact the VOIP setups much more than the technology calls for. There is also a concern that the hardware, like mic or speakers might get lost if they aren’t connected to the bus.

Other solutions, however, go with more modern solutions with Bluetooth headsets, where the driver have both hands free, instead of maneuvering a mic with one hand, while driving. Perhaps it isn’t too far fetched to think that it is just a matter of getting used to the idea that a bus driver can use a headset just as an airline pilot does.

Classic radio communication is one-way communication. So called simplex communication. This is normally used when it comes to VOIP for public transport as well. It keeps the talk to a minimum with very concrete content, which means the data use is much lower. It wouldn’t be a problem to use two way communication for VOIP, or even in a more advanced radio system with support for it, but in most cases, perhaps for traditional reasons, simplex communication is the preferred option.

Communication setup

A common setup is that the driver sends a call request to the dispatcher, who in turn calls the driver. This setup is a way of reducing the risk of overwhelming the dispatcher if many drivers call at the same time. This setup might not work if the drivers aren’t allowed to talk while driving, since it will be difficult for the dispatcher to time the call to when the bus reaches a stop.

Other options, like the dispatcher being able to contact all vehicles at once, all vehicles on a certain route, in a certain area or in a pre-built group are all software-based solutions, which means that with an open, standardized system with the possibility to add that type of solutions, it’s just a matter of software development. These functions, all interesting for public transport, speak in favor of VOIP in comparison to radio, since VOIP is much more dynamic and easier to modify. The setup by that reason benefits greatly if it is integrated with the fleet management system, so that changes in vehicle groups automatically could be reflected in the VOIP group setup.

In some cases, there might be a mix between radio and VOIP, where you use the radio solution for communication, but the VOIP backend solution as interface for drivers and dispatchers. This way, everything is set when the day comes to change net from radio to mobile.


When it comes to economy, the most common setup is a license per month and user. This is probably the payment model that will be predominant. There is a need of a monthly fee to cover support, especially since the initial cost of the system is so low.

Available apps

There are some app-based solutions already on the market today, which can be integrated in an Android-based environment and used as base for VOIP. However some of them fail stress tests. The quality isn’t good enough for commercial use. They work fine for private use, but not in a professional environment.

Others might work well and have all the features you need, including smooth integration, and a stability even better than a regular mobile phone call, but they might instead be too expensive to use in the long run.

The availability of apps, however, shows the benefit of working with an open Android-based environment, and being able to benefit from development made for other use and for other reasons, but that might suit your needs.

Arguments in favor of VOIP

The most important benefit of VOIP compared to radio is without doubt reduced costs. A radio infrastructure is expensive to build and maintain, since it is so specialized, compared to the mobile net, which has millions of users to share the costs.

The VOIP solution is powerful and versatile, with the possibility to easily change the software-based backend system with group handling and other features.

With an internet connection and display already in place, the hardware need is very limited. It is easy to install, and it demands much less administration than classic radio or phone. With a software-based solution, all you need is either a headset or a mic and speakers.

Another benefit is that there already today are app-based solutions in place that can function as a base for developing the system you need, and thereby taking advantage of an open Android environment with standardized solutions, instead of having to reinvent the wheel.

Software solutions are scalable, which means that once a system is developed, the cost for adding users is much lower.

Part from a radio infrastructure that is needed for a classic radio solution, you also need an antenna, a receiver and a driver interface unit of some kind. This adds cost to every installation, compared to VOIP.

Most countries at least in Europe today have a mobile coverage reliable enough to sustain a VOIP solution.

With no system at all in place, the VOIP system is easier and more cost effective than the alternatives, except of course for mobile phones. With a mobile phone solution, however, you miss out on a lot of core functionalities, like dynamic group handling that lets you set up communication with all vehicles on a certain route, in a certain area or any other pre-built group that fits the specific needs of the operation.

The VOIP systems don’t use much data, which means that in most cases it won’t exceed the data plan already in place.

The vital function of assault alarms are often distributed through the mobile network, and you might argue that the step of migrating from radio to VOIP is in some ways is a smaller step to take.

Challenges with VOIP

The most significant uncertainty with VOIP is mobile coverage. Focus is transferred from building your own network to get coverage, to put your trust in the mobile network, which isn’t always reliable in the countryside, especially in mountain areas.

Another factor is that data communication might not be prioritized when the net fails, since phone calls with the possibility to make an emergency call often is considered more important than data traffic. With a radio solution, you have control over what to prioritize.

With a radio system and a mobile phone, the driver has two redundant systems to use in case of an emergency. To get redundancy with VOIP, you need to use two different mobile operators.

Since VOIP is digital, you either have connection or you don’t. It isn’t like when you have a bad phone line or radio connection, where you get a lot of white noise, but are still able to maintain a connection. An IP signal goes silent if the connection is bad.

The future

If you have invested in a classical radio system, you might want to use it for its entire technological lifespan. However, VOIP is in the end more cost effective and easier to adjust to new demands, so it could be wise to think about not to continue investing in a system that might not be the right path for the future. The economical lifespan is sometimes shorter than the technological.

It is most likely that VOIP will be the leading public transport communication solution in the future. However, it is difficult to predict when the big shift takes place, since many parties have invested in radio systems.There is still also a great uncertainty among decision makers, whether VOIP is reliable enough.

The interface for radio is also still in development, which shows that a big part of the public transport business still believes in the radio option, and probably will for some years to come.

Another factor to take into consideration is the political aspect. Some authorities have invested in a certain solution and push for it to be used. In such cases the shift might be significantly delayed.

Addition regarding security – published 21 March 2019

After receiving input that we missed the important aspect of security and guaranteed availability, we decided to update the blog post.

Security classification and availability

One problem with VOIP is that a Mobile network isn’t a security-classed communication solution. This means that during events, such as royal or presidential visits or other high-profile occasions, the Secret Service might shut the entire mobile network down for security reasons. The same thing happens during suspected terrorist activities or other major security threats. Then VOIP won’t work. Private radio networks, however, will still work, as will public TETRA security classed networks.

Overload during big events

Another issue is big events, where the mobile network might falter due to overload. During major sports events, concerts or big holidays like New Year’s Eve, the mobile networks sometimes are overloaded when public transport communication is needed the most. This is a concern for all VOIP solutions.

Major cities

In a city like London, for example, extraordinary events are commonplace, which affects public transport agent a great deal when deciding between VOIP and radio. A big public transport actor in London just launched a new digital radio network with the motivation that they must be able to reach the vehicles during these events.

Parallel systems

Since mobile operators cannot guarantee the availability, one option might be parallel systems and integrated solutions to get the best out of both worlds, where most traffic goes via VOIP and radio is used only when the mobile network goes down. This would provide the low costs of VOIP and the reliability of radio. It might, however, be difficult to arrange such a setup without ending up with the costs for both VOIP and radio instead.

Guaranteed availability versus price

Mobile operators cannot provide a Service Level Agreement – SLA, because they can’t guarantee the service of the net. This means that you must decide between the cost reduction of VOIP against the guaranteed availability of a private or public radio solution. The mobile networks have relatively high availability, but no guaranteed accessibility. For basic functionality in a high percentage of the cases, VOIP works. The last few percent risks costing you a lot to solve. The question is; can you live without functionality in those cases? VOIP is so much cheaper that it might be worth weighing the risks of not having a guaranteed availability against the savings with a VOIP solution.

RAKEL – the Swedish public TETRA net

In Sweden, the public TETRA net, used by for example the police and fire brigade, is also available for public transport agents through rental of equipment and a monthly fee. This is an attractive solution that takes away the need of a private radio solution. It is quite expensive, though. There are also other concerns regarding a public security net. For example, if a radio breaks down, it takes time to have it repaired. First, the radio must be sent to one place for the encryption keys to be removed before it can be sent somewhere else to be repaired. Then it is sent back to the first place for the encryption keys to be reinstalled before the radio can return to service. This means that a broken radio can be away from service for a month. During that time, you can of course use a replacement radio, but then you need to be able to handle the temporary integration of the replacement radio ID in your own system. This issue must also be considered when deciding between a VOIP solution, a private radio network and a public security network.

Negotiate with the Secret Service?

Another option regarding VOIP, for major players within public transport, is to put pressure on the mobile operators to provide a service level agreement or perhaps negotiate directly with the Secret Service regarding if it is necessary to shut the mobile network down completely, or if certain customers could remain connected even during extraordinary circumstances. The prospects of success for such an endeavor might be questionable, but eventually some solution should be possible in this area.

Disclaimer: The content of this blog post is the author’s opinion and doesn’t reflect the opinion of any other person or organisation.