TETRA
interwork TETRA and broadband,
either temporarily as they install their
systems, or permanently because they
believe that broadband speech will lag
behind data.
“The interworking functionality is
intended to maintain as many services
as possible across the link. One to
many, many to one or many to many.”
One area of particular interest to
Murgatroyd is security, something
which he has been involved with
throughout his career at ETSI.
Discussing the ongoing evolution of
this in relation to the TETRA standard,
he says: “TETRA has always had air
interface encryption between the base
station and the device, just like you’d
have on a GSM or 3G/4G network.
“At the same time, a percentage of
users also require greater protection, as
well as separacy of agencies using the
network. Having been quite heavily
involved in that, I have to say, the endto
end encryption side of TETRA is
extremely effective.
“We’re now developing new
algorithms with a longer key length for
air interface encryption. We haven’t had
notification of any attacks on public
safety TETRA, but nevertheless we
need to future-proof things.”
He continues: “Going back to the
subject of interoperability, the question
now is how do you re-encrypt end to
end across the broadband network?
More to the point, how do we make
sure that the standards are implemented
in relation to this?
“As with everything else, it’s all very
well saying what the requirements are
and writing a standard, it’s a different
thing to get industry to adhere to it.
It’s the demand which makes the
standards viable.”
Asked what he believes the main
technical issues might be when it comes
to standardisation, Murgatroyd suggests
that one could lay in the variety of
different ways there are to achieve
hybridisation. Examples he gives of this
include the aforementioned hybridised
terminals themselves, as well as joining
nets via a dispatcher patch, connecting
the same audio to both systems.
Regarding encryption across
broadband and TETRA networks,
meanwhile, this will likely have to
be solved by what Murgatroyd refers
to as an “intermediate transcoding
step within an interworking function
IWF”. This is because “pure endto
end encryption requires a straightthrough
connection across both the
I actually have an enormous amount
of faith in commercial networks when
it comes to the provision of missioncritical
crucial features such as priority and
pre-emption, without which no
network meant for first-responders
could function.
With our time coming to an end,
I ask him to clarify his comments.
“I actually have an enormous amount
of faith in commercial networks
when it comes to mission-critical
functionality,” he says. “A huge amount
of resources and preparation have gone
into these projects, after all, the most
obvious examples being FirstNet and
the Emergency Services Network.
“Nevertheless, these are still
commercial networks, meaning there
are factors which always need to be
considered. That obviously includes
priority and pre-emption, but also the
physical infrastructure itself. What’s the
overlap coverage like if a base station
falls over? Is the contingency there to
deliver the same level of service that
they’re used to with TETRA?”
He continues: “This obviously
applies to any national communications
system, which is another reason why a
lot of governments are quite cautious
when it comes to just abandoning what
they already have. An illustration of this
is the original roll-out of TETRA in the
UK, where we made a large number of
assumptions which didn’t actually turn
out to be quite right.
“One of these was that base stations
only ever fail one at a time, which of
course is not always the case. You also
have to take into account the possibility
of a power outage, where you could
lose 30 or 40. What happens if there’s
insufficient back-up power, which was
precisely what happened on more than
one occasion?”
If what Murgatroyd says is correct,
it is clear that TETRA possesses an
extremely viable future. It continues
to be a solid, well-specified and wellsupported
technology, the use of which
is as varied as the industries in which it
is rolled out.
Brian Murgatroyd will be taking
part in the Critical Communications
Week panel discussion ‘The future
of TETRA’. His co-panellists will
include Iain Ivory, David Chater-Lea
and Ken Rehbehn.
functionality
TETRA and broadband networks,
while retaining synchronisation”.
According to Murgatroyd, this can be
facilitated by using the TETRA codec
in the broadband system. However,
this would require broadband terminals
to be able to use both the TETRA
codec as well as the broadband one.
“This may be complex to achieve, so
the compromise of an intermediate
transcoding in an IWF is fine, as long
as the latter is contained in a secure
environment,” he says.
It is obvious that TETRA currently
possesses clear advantages over
broadband, particularly when it comes
to mission-critical push-to-talk. Indeed,
it has been the gold standard for
years when it comes to this area
of functionality.
The same cannot be said, however,
for its short data service, something
which, in terms of ‘non-voice’, is
essentially the narrowband equivalent
of being able to send an SMS. Given
the limitations of the technology in this
regard, how is it likely to evolve purely
from a use-case perspective? What can
users expect to see over and above what
they have now?
Addressing this, Murgatroyd says:
“The short data service has actually
been very widely used, which is
something that people may not
be aware of. This came to the fore
particularly with location services/
devices, enabling organisations to know
where their resources are. Personally, I’d
say this aspect of functionality has been
fully developed, with the standards
amended accordingly.
“This of course is not to say that
the implementation of the technology
itself hasn’t moved on, something that
you can see in the increasing roll-out
of TETRA paging. This is apparent in
somewhere like Germany, where the
fire brigade relies on a huge number
of volunteers.”
Lack of faith
Earlier on in the interview, Murgatroyd
expressed what seemed like a potential
lack of faith in commercial networks in
terms of resilience. That being the case,
you also have to wonder what
his opinions are in relation to other
October 2020 @CritCommsToday 55