cabling
Some transceiver solutions now
leverage Wave Division Multiplexing
(WDM), a technology that enables
a single fibre to support multiple
wavelengths (in effect, separate
‘data lanes’). The IEEE 100GBaseLR4 standard – supported by every
major vendor – establishes four
25Gb/s lanes on each of two single
mode fibres to deliver an aggregated
100Gb/s, enabling 100GE links
with a reach of up to 10km. The
100GBase-CWDM4 standard uses
exactly the same structure to deliver
100GE over 2km on just two single
mode fibres. There are also several
multimode fibre WDM solutions on
the market that are not currently
standards approved.
Another approach is through
a well known industry leader’s bi26
directional (BiDi) transceivers. BiDi
requires multimode fibre and can
support 40Gb/s transmit speeds by
aggregating two 20Gb/s optical lanes
– one per fibre – with the receive
link put together in the same way.
Distances over OM3 and OM4 are
down to 100-150m but then we’re
talking about the backbone of a data
centre here, not some elongated
campus LAN.
But hang on a moment – will any
aggregated 2-fibre solution really
be able to attain the blistering high
speeds of future standards like 400G,
over any kind of usable distance? And
when the maximum capacity of two
fibres eventually reaches its zenith,
isn’t there a risk that data centres
which have taken this path will be
‘locked-in’ to the proprietary roadmap
of their transceiver manufacturer?
Some will find that a reassuring
prospect, but others will be concerned
that such a wide variety of choice is
no longer available to them.
Another school of thought favours
parallel optics and the aggregation
of greater numbers of fibres. Using
the current Base-12 cabling standard
creates links based on increments
of 12 fibres rather than two, and
makes use of MTP connectors. MTP
has become the norm for many data
centres, and that’s important as far
as future flexibility is concerned.
Even where LC connectors still
feature heavily at the end of links, the
backbone connectivity is increasingly
MTP domina