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Chapter 3
Cable Tests
xGenius has the ability to check wiring and performance of Ethernet cables or optical
fibres to make sure they will operate as expected when connected to the network.
Cable testing can be used to estimate the cable length, recognise cabling types or
detect wiring faults. Performance of optical fibers is measured in terms of the received
optical power.
3.1.Electrical Test
Electrical cable test requires an special operation mode which prevents the unit
sending any frame (See section 2.1). When the unit is configured in Ethernet cable test,
mode, the port mode becomes Cable test (port A) and Link (port B) and there is no way
to change the port mode unless the general operation mode is set to something
different of Ethernet cable test.
In this operation mode the test unit could have a network link in the remote end of the
device under test (the cable) or not. Depending on how the cable is connected, it would
be possible to compute different results.
3.1.1. Basic Principles of Ethernet Cable Wiring
Twisted pair cables for Ethernet LAN applications generally come in groups of four
pairs (8 wires). Only two of the four pairs carry information at 10 and 100 Mb/s but all
four pairs are simultaneously used in 1 Gb/s links. There are many possible pair
interconnections that would work, but only two of them are standard. These are known
as T-568A and T-568B wire maps. Usually, all four pairs are always connected, but for
10 and 100 Mb/s operation only pairs 2 and 3 are used. 1 Gb/s port and cable wirings
are designed to be backwards compatible with slower 10 Mb/s and 100 Mb/s interfaces
so that the same Gigabit cable can be used for all bit rates. Some cables designed to
operate at 10 Mb/s and 100 Mb/s may have only connections necessary for
transmission at these speeds. These cables are not compatible with the 1 Gb/s bit rate.
Ethernet cables may have poor performance or may not work at all if wires are not
properly connected.
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