How to build maximum availability also in the PMR future

Published: 2 Sep 2016
Topics: TETRA future
Reading time: 6 min

Governments and organizations whose operations rely on smooth communications have chosen to set up dedicated communication networks. Their prime objective: availability. After all, failure in communications could jeopardize operations and put lives at risk. Public safety organizations in particular need their communication systems to be very reliable and always available.

What does availability mean in practice? How is it built? And how is it with public safety broadband?

Availability means that the system, its resources and applications are accessible when the user needs them. You can use the system when you need it.

What can make a system unavailable

The most common reason why a system becomes unavailable is a natural disaster such as a heavy storm. A storm can destroy equipment, cut transmission, or cause power breaks. Other reasons include human error, software faults, or even cyber-attacks. In addition, a traffic overload on the system will degrade the service for the users. The service may become completely unavailable in an extreme overload situation.

How availability is built

An unavailable system is of no use. PMR systems are critical for the users so they are built for high availability. Over the decades many different availability characteristics have been developed. For example -

  • Hardware redundancy helps make sure that losing one piece of equipment will not stop the whole system. There is a spare piece that will take over.
  • Back-up power schemes: if a storm cuts off the electricity supply to base stations, an uninterruptable power supply (UPS) and/or backup generator can keep the systems going.
  • The network can deploy at least two alternative routes from each base station to the switch. The system monitors its transmission links and if links are broken, reroutes the traffic. So if one link fails the transmission will still get through.
  • Base station fallback means that a base station can provide communications to the users in its coverage area even when it has lost its connection to the switch (which is usually the brains of the network).
  • Direct Mode Operation (DMO) is used when there is no base station coverage. The communications go from one radio device to another.
  • Priority access helps guarantee that the service is available for the most important users - even in heavy traffic. An example of an extreme case would be to set a base station to refuse service from lower priority users.
  • Capacity guards can monitor that any application does not over-use or overload the system, and adjust them if needed. This way, the network can be used to its full capacity without compromising availability.
  • Exclusive capacity can be set up for certain users. For example, a certain base station can be dedicated to serve those users exclusively.

These are just eight examples of measures that help build better availability for a PMR system. And all these measures are in place in the best TETRA systems.


This is how things are now, but what about the future? What about public safety broadband?

Well, it is like with any new technology. The new does not automatically inherit features and capabilities from other technologies. Capabilities – such as availability - have to be built in specifically. All these availability measures, for example, are not in place in today’s commercial broadband networks.

Commercial network operators have to consider the cost of investment against the possible extra revenue. It is also more difficult to control the traffic loads in a cellular network. That is why operators do not guarantee the availability of these commercial networks, not even for the users whose traffic has higher priority.

How to guarantee best availability while evolving to public safety broadband

The TETRA network operator can resume the role of a mobile virtual network operator for a hybrid network. Critical voice and messages continue to run in the dedicated narrowband network. The commercial networks in the hybrid networks will serve the data users. Today, this data will not be mission-critical.

Own dedicated broadband can bring additional service to some areas. This kind of add-on broadband network could be built to withstand power blackouts. And because it would be dedicated to the owner, it could offer high availability to the users. But if there aren’t frequencies available, a dedicated network cannot be built.

It will take a long time before commercial broadband networks are mission-critical. It will also take a long time for any government to build a nationwide, dedicated broadband network for public safety. That is why public safety users will use today’s narrowband voice networks for a long time.

The long time is not a problem for TETRA operators and users. On the contrary, they can adopt hybrid networks and gradually evolve towards public safety broadband.

The availability of the complementary broadband networks in the hybrid model is only as good as it has been made. For example, broadband services may become unavailable during times of high traffic loads. Or when a power blackout has taken out the broadband base stations – if they have no backup power.

But commercial networks will be improved to better meet the mission-critical needs. Hybrid communications will be better and better. And suitable radio frequencies may become available for setting up a dedicated broadband network, too.

Smooth PMR evolution

Let’s not forget that TETRA over 4G is possible today. If the TETRA server is equipped with the right Tactilon software, users can install an app and get full TETRA services on a smartphone. This is an interesting option for organizations who prefer to use smartphones for communications and who do not require mission-critical availability.

When commercial broadband networks have adopted enough availability measures and meet the mission-critical requirements, users can choose whether to use TETRA services on a smartphone or to continue with TETRA radios. Group communication can continue to work the same way.

This is truly smooth PMR evolution.

Do you need pointers to your network's evolution path to mobile broadband and mobile apps? Start by looking at these 14 great resources that help you evolve your PMR network to broadband, provided by Key Touch magazine.

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The Mission Is Critical blog gives you insights into professional and public safety broadband, mission critical user experience, secure and critical communications, hybrid narrowband-broadband solutions and dual-mode devices, and Tetrapol and TETRA radios.