26 Jun 2018
Three factors will come together to boost the available
capacity: more spectrum, especially in the 20-100GHz range,
millimetre waves; more efficiency, thanks to steering these
high-frequency waves right at the user; and tiny cells, meaning
frequencies can be reused – if you have the fibre
At the same time the internet of things (IoT) is going to
change the demands on the system, so dense networks will be a
necessity, not an option. One of the requirements of the future
networks is low latency – of one millisecond or
If you have a spare half-hour, go to the website of this
year’s Optical Networking and Communication
Conference (OFC), which took place in San Diego. There, Marcus
Weldon, president of Bell Labs and CTO of Nokia, gave an
outstanding presentation of why we will need all this capacity
and what the industry is doing to supply it.
At the same conference, scientists from Google and NEC also
talked about how they have been able to double – maybe
triple – the capacity of a subsea cable. They showed
what they can do to push long-haul limits, but Weldon explained
eloquently that it’s on short-haul connections
that the industry needs to focus.
Weldon explained in that OFC keynote speech that industrial
networks – for connected vehicles and so on –
need a latency of no more than 1ms. Why? He didn’t
say this, but this is my rough calculation. Take a car going at
50km/h (or 30mph): in one millisecond it travels 14mm. If
you’re going to avoid collisions with other
vehicles, which are likely also networked, or with people,
whether pedestrians or cyclists, which aren’t,
you’ll need that sort of accuracy.
It’s not just vehicles. Industrial machines and
other IoT services will need low latency. A round-trip time of
1ms means the distance to and back from the data centre must be
100km or less.
If you’re in Hong Kong, London or New York,
you’ll probably have a data centre within 50km
– though maybe not the right data centre. What happens
when you get more than 50km away: does your autonomous vehicle
lose its autonomy?
So welcome to the world of the edge cloud – which
makes one realise how prescient were the founders of
EdgeConneX. Data will need to be no more than 50km from
everyone. That will mean a complete rethink of
everyone’s ideas of how networks are
It gets worse, because part of this surge in demand for data
will come from the virtual radio access networks (vRANs) that
will be used for 5G mobile. These base stations will need high
capacity but also even lower latency in their control plane.
Weldon put it at 30 microseconds (30µs), around a
thirtieth of the current 1ms requirement.
So, does that mean data needs to be stored no more than
1.5km away from anyone on a vRAN? Quite a challenge.
One of the more intriguing presentations at the OFC was from
a joint Google/NEC team on how to squeeze more and more out of
subsea cables. They said they have doubled the performance of
the Faster cable linking Taiwan to Oregon, and they believe
they can go on to triple it.
The 10,000km cable was originally designed to carry traffic
at 2 bits/second/hertz, but using artificial intelligence (AI)
techniques they increased spectral efficiency first to 3b/s/Hz
and then to 4b/s/Hz – twice the original
Toru Kawauchi, general manager of NEC’s
submarine network division, said they’d used
machine learning algorithms in place of the previous
"deterministic models of non-linear propagation" through the
Google and NEC tested the performance on the Faster cable
itself in a field trial carrying live traffic from Google data
centres. NEC has also carried out offline field trials over
dark fibres with even more promising results. They used fibre
of the same length and achieved spectral efficiency of
5.68b/s/Hz and made other measurements that promise 6.06b/s/Hz
– three times the original design specification of the
Faster cable. That means 6b/s/Hz is a "realistic target", said
Both the Google/NEC team and Weldon from Bell Labs paid
frequent tribute to Claude Shannon, the Nobel prize-winning
Bell Labs mathematician who 70 years ago this year worked out
the theoretical limits to how much information you can carry on
a particular chunk of spectrum.
We’re pretty much at that Shannon limit now:
NEC is close with Faster in the subsea world, and the wireless
world is nearly there too. Densification and millimetre
spectrum are the only hopes to get more wireless capacity. For
subsea? More wavelengths and more fibre.