Interoperability
we’ve got quite a reasonable level of support from interested
vendors in pursuing that,” says Gray. “TCCA would engage
an independent test house to manually analyse the test
traces from the MCX Plugtests and pre-certify people’s
equipment as being conformant to the standards and being
interoperable to other conformant equipment. We hope
to be able to start to do that soon after the fourth MCX
Plugtest in September.”
Obviously, this approach is less than ideal, given that the
manual nature of this testing may create capacity issues,
and Ludwig is currently trying to determine “how many
interested vendors are there, how many implementations
they want to test and how many test cases we need to
test to get some confidence in standards compliance”. He
adds that capacity is an issue with the TETRA IOP testing
programme, as that’s also done manually and “this has
resulted in test sessions of several weeks and months for
one infrastructure manufacturer”. However, Ludwig adds
that TCCA only sees the pre-certification programme as an
interim solution.
The second approach is that the Public Safety
Communications Research (PSCR) division of the US
National Institute of Standards and Technology (NIST)
“has quite a substantial budget of investment funds that it
wants to spend on getting the mobile broadband solutions
available and active in the world, and it has recently come
out with a call for proposals for incorporation of missioncritical
voice testing in test equipment,” says Gray. “That
would essentially do what I mentioned before of getting
one or more test equipment manufacturer to provide the
suitable test cases in their test kit. We’re working with several
potential partners in being involved in that in much the
same way as we are involved in the MCOP Mission Critical
Open Platform programme, which is funded under the
same NIST/PSCR budget.
“So, we’re hopeful that with these two strands running
more or less in parallel, we can ultimately end up with
a regime and approach that provides the quality of
interoperability and conformance testing and certification
that the industry needs.”
The commercial factor
It is also worth noting that interoperability isn’t just a
technical issue. The decision to allow different MCPTTbased
applications and also users on different cellular
networks, either using the same or different apps to talk
to each other, is largely a commercial one. Gray says the
pressure needed to ensure that this is enabled “has to come
from the bottom up – unless there’s a compelling reason
then the individual carriers will probably want to lock
their users into only using their service”. He adds that the
“compelling reason” is precisely what led to the creation of
FirstNet. In other words, the need for a nationwide,
single operable solution that in situations involving multiple
agencies from multiple areas – and potentially on
different carriers – allows them to communicate and work
seamlessly together.
“If the ecosystem allows it to just go on developing
in a disparate and unharmonised way, they’ll end up
looking back and thinking ‘oh dear, we’ve recreated all the
problems we had with LMR interoperability… purely for
political and commercial reasons.” He adds that “the open
market has its advantages”, but it still has to be regulated so
interoperability is enforced.
Similarly, political and commercial considerations will
have a big role to play once interworking between MCX and
LMR (TETRA and P25) has been standardised. “3GPP can
develop an interoperable connection towards LMR (TETRA
and P25) just as ETSI and ATIS can for TETRA and P25
respectively. But whether any or all manufacturers actually
implement those is a completely separate discussion, it’s
totally their commercial decision as to whether they think
it’s worthwhile or whether they want to try to promote their
own proprietary approach,” says Gray. “As TCCA, we would
always very strongly promote and require the standardised
approach since it’s the only way to maintain an open,
competitive market.”
Of course, interoperability is not the only thing that is dear
to the hearts and minds of end-user organisations. As Ludwig
points out, performance metrics such as call set-up time
and voice delay “will be a key criterion for users moving to
broadband MCPTT because they have to be at least as good
as they are in TETRA or P25; if they are not, users will have
no motivation to move to broadband”. He understands that
PSCR in the US is working to define test set-ups and measure
these key performance indicators.
He also highlights the scale of the challenge, given that
there are so many different types of equipment involved – “It’s
the set-up of the whole LTE network, of the radio access, of
the MCPTT server, the devices, the MCPTT software, and
all this needs to be optimised across all the systems.”
ETSI’s Arora adds that so far, call latency and packet loss
have not been tested at the MCX Plugtests events, “but these
kind of performance tests cases are something that we might
consider adding”.
We have seen that the work to iron out any kinks in the
mission-critical standards is progressing well, and while
the test and measurement certification roadblock remains,
the industry is working hard to address this, both through
engagement with T&M vendors and through pursuing
several other approaches. That said, there is no cause for
complacency – if user organisations are serious about
interoperability, constant and concerted pressure needs to be
applied to prevent the industry from sleep-building the next
Tower of Babel.
July 2019 @CritCommsToday 15
Adobe Stock/pict rider
Full cross-carrier,
cross-application
interoperability
won’t happen
without strong
co-ordinated
pressure from
public safety
agencies