The security of the UK's £2.5bn Airwave police Tetra network was this week brought into question by analysts and experts from the Israeli army. The army is investing in Tetra to provide tank phones for battlefield communications.

Brigadier general Moshe Markovitch, of the Israeli defence force communications branch, claimed that Tetra needed at least four channels to be secure. The UK's police force only plans to use one channel, except in densely populated areas.

Without additional channels to provide security, Markovitch did not believe that the police could be sure that Airwave would not be jammed.

Tetra was designed to hop channels, increasing resilience when multiple transmission channels are used in the network.

Nigel Deighton, research director at Gartner, said that any radio system could be jammed but that if this happens, a Tetra network can switch to another channel, allowing communications to continue.

"The more channels and power you use, the more resilient your Tetra network becomes," said Deighton. "It means that someone would have to block all channels, which would drive up the cost of jamming the network."

Ray Mason, implementation manager at BT Airwave, confirmed that the system would use multiple channels in built-up areas to provide the required coverage and capacity. "Non-dense areas will get fewer base stations and only one radio channel," he said.

When radio frequencies from a base station are jammed, Tetra offers an alternative way of making contact. The technology supports Direct Mode, so that handsets can bypass base stations and communicate directly with each other.

However, the BT Airwave handsets do not automatically switch to Direct Mode, but keep looking for the network when they lose connection. If terrorists jammed the network, the police could mistake this for a quiet day, and not realise that they should manually switch handsets to Direct Mode.

"We don't know of any terminals that automatically go to Direct Mode when they lose connection," said Mason. "They keep hunting for a signal, but you could presumably switch them manually."

First published in Network News