TEST & MEASUREMENT
practices to ensure that any Ethernet device could connect
to, and operate on, a cabling system that was designed in
accordance with the standard. Therefore, once installed,
cabling is tested with a LAN cable certifier to ensure the
completed system meets the performance promised by the
individual components.
Defining permanent links
The installed cabling that services a network device is called
a Permanent Link (PL). A PL is terminated at the network
equipment room into a patch panel (socket), can be up to 90
meters long, and is terminated at the device end into a box
or wall plate with another socket. Equipment/patch cords
totalling 10 meters in length can then be used to connect
the network switch and networked devices to the PL. The
maximum allowed length of the Channel is 100 meters.
When testing PL’s, a certifier uses special test cords
with tuned RJ-45 plugs to measure the performance of
the connections at each end of the PL. The measurements
are compared to the standards to determine whether the
installed PL passes or fails certification.
The diagram below represents testing a PL with a cable
certifier. The angled bracket represents a tuned RJ-45 plug
that is part of the certifier’s test cord. The portions of the
diagram in green are measured during the test. The red
portions of the diagram are not measured during the test.
Cable certifiers measure small signal changes at high
frequencies and use proprietary test cords and connectors
to provide high accuracy and repeatability. A tuning process
creates ‘centred’ connectors that will always measure the
same when connected to a socket. Therefore, every brand of
certifier with an approved test cord will show the same result
when testing the same socket.
Testing channels
Cable certifiers can also test channels that end with a Plug
instead of a socket. However, the connection between the
channel adapter and patch cord is not tested because the
socket in the adapter is not centred. A non-centred socket
cannot be used to test the performance of a plug. How does
this apply to an MPTL? With MPTL, one end is terminated
with a socket, the other with a plug.
When certifying an MPTL, one would expect that all they
need to do is change the adapters on the certifier so one
end has the test cord with a plug and the other end has the
adapter with the socket. Unfortunately, it’s not quite that
simple and measuring the performance of the plug at the
end of the MPTL takes special care.
A non-centred socket cannot be used to measure the
performance of a plug so simply changing the adapter
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