cabling
limitation of just 5m-7m, these direct
attach assemblies are restricted for
use with ToR switch configurations
where smaller access switches
are deployed in each equipment
cabinet and directly connected to
the equipment in that cabinet. While
SFP+, QSFP and other twinaxial
cable assemblies support low power
and low latency, which can be ideal
for supercomputing environments,
there are some considerations.
Standards based Category
6A and higher cabling supports
autonegotiation. Direct attach twinaxial
assemblies do not. Autonegotiation is
the ability for a switch to automatically
and seamlessly switch between
different speeds on individual
ports depending on the connected
equipment, enabling partial switch
or server upgrades on an as-needed
basis. Without autonegotiation, a
switch upgrade requires all the servers
connected to that switch to also be
upgraded, incurring full upgrade costs
all at once.
Unlike Category 6A and higher
cabling that works with all Base-T
switches, regardless of speed or
vendor, higher cost proprietary
direct attach twinaxial cable
assemblies may be required by
some equipment vendors for use
with their ToR switches. Proprietary
cabling assemblies can require cable
upgrades to happen simultaneously
with equipment upgrades. In other
words, currently installed direct attach
cable assemblies will likely need
to be replaced if another vendor’s
equipment or a higher speed switch
is deployed. Some ToR switches
are even designed to check vendor
security IDs on the cables connected
to each port and either display errors
or prevent ports from functioning
when connected to an unsupported
vendor ID. With recent advancements
in technology now enabling
10GBase-T switches to drop in price
and power consumption, standards
based Category 6A cabling or higher
makes the most sense for today’s
switch-to-server connections in the
data centre.
Another reason to stay with
standards based cabling for switchto-server connections at the edge
stems from the fact that switch-toserver connection speeds continue
to push beyond 10Gb/s and ISO/
IEC has already initiated work on
next generation cabling to support
upcoming IEEE 802.3bq 25 and
Today’s flattened
architectures with
fewer switch tiers result
in longer cable runs
between switches.
40Gb/s Ethernet (ie. 25GBase-T and
40GBase-T) over balanced twistedpair copper cabling.
25GBase-T and 40GBase-T
both build on the existing and well
established 10GBase-T technology
and are intended for operation over
30m of future ISO/IEC Class 1
cabling constructed from Category
8.1 components and Class 2
cabling constructed from Category
8.2 components characterised to
2GHz. Class 1 and Class 2 cabling
will continue to share open and
common specifications, ensuring
interoperability and backwards
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