FIBRE STANDARDS
By Paul Cave, Technical Product
Manager, Excel
When looking for a network installation option offering
longevity the future is singlemode fibre
www.excel-networking.com
I have been asked on numerous occasions this year so far
about whether it is best to install multimode or singlemode
fibre as a future-proof strategy on a new project. While there
are reasons to suggest that multimode will still have an
important place in small to medium size enterprise networks,
the evidence is indicating anyone planning mid-large
Enterprise or any form of data centre should only consider
singlemode when planning for the future.
While there has been much debate in the media over
the last few years about whether singlemode or multimode
is the sensible approach to be adopted within data centre
environments. This discussion has been made even more
complex with the introduction of OM5 fibre over the last 18
months.
If we take a step back to look at the basic
recommendation of any standard, being that you should
design your infrastructure to be able to support two
iterations of technology or hardware upgrades, it sets the
foundation for some interesting arguments.
For a number of years, IEEE 802.3 task force has been
working on higher and higher Ethernet speeds, not only
going from 10G to 40G and 100G, but they have also been
exploring 25G, 50G, 200G and 400G primarily for use in
data centre environment. In December 2017, they published
802.3bs for 200 and 400G over fibre.
There are currently a couple of basic premises to this
article; firstly singlemode systems are recognised to be more
expensive than multimode, purely due to the current cost
of the Electro-optics. However, the greater transmission
distance, higher bandwidth, upgrade capability and future
developments based on singlemode should outweigh the
cost argument in time. While it’s possible to use multimode
fibre, for IEC 802.3bs and these higher speeds it would
take 16 parallel fibres to support 400G transmission with
a limited distance of 100m. This development starts to
become a watershed moment when you consider that the
same performance can be achieved up to 500m using 4
singlemode fibres.
In a similar vein, we also need to consider the fibre
channel used in storage area networks (SANs), which
is estimated to use approximately 25-30% of the fibre
installed in data centres. The Fibre Channel Industry
Association (FCIA) has based their roadmap for the future
on effectively doubling transmission speeds every few
years. In 2016, FCIA introduced Gen6 Fibre Channel, which
consists of two key speeds – 32GFC in the SFP28 form factor
and 128GFC in the QSFP28. With multimode they both have
the same distance limitation of 100m, while singlemode is
capable of 10km distances. Currently, 32GFC uses duplex
fibres while 128GFC is based on quad lanes using MPO/MTP
connectivity for both multimode (100m) and singlemode
(10km) fibre.
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Cost considerations
Cost may not be as straightforward as some think. While it’s
agreed that multimode electro-optics are currently cheaper
by a significant amount, the landscape is changing and
potentially at pace. At the same time, some will highlight
the development of OM5 as being the next ‘shining light’ in
this reasoning. But they’ll be missing some key points:
OM5 offers longer lengths than OM4
If you look at the reality, the advantages are minimal if at
all. In some cases it’ll only offer an additional 50m over
what can be delivered by OM4.
OM5 will reduce costs
Again, this is a fallacy. At this present moment in time,
OM5 fibre and connectivity (Patch Leads and Pigtails etc)
are approximately 10 times more expensive than the
equivalent singlemode products. As for the transceivers,
they’re currently closer to singlemode costs, rather than
multimode, due to volume and demand. Also, bear in mind a
forthcoming argument regarding the OCP.
OM5 will create higher density
How? While it may be the case in relation to OM3, this
argument doesn’t stand up against OM4, which can support
the same density but over shorter distances. When you
consider singlemode it’s already been demonstrated that
a quarter of the fibres are required to provide a greater
distance. Furthermore, it’s common practice to ‘break out’
higher bandwidth ports to increase port density; this is not
possible using SWDM and OM5 fibre.
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