Cross-Linking With Two Patch Cables

In networks, the
supremacy of coax cable is a thing of the past. Nowadays, Ethernet
connections are made using UTP cables. The BNC
plug has yielded to the 8-way RJ45 plug. Previously, coax cables were
daisy-chained from computer to computer and terminated at the two ends
using 50-_ resistors, but modern networks use central ‘socket boxes’
(switches and/or hubs) to interconnect everything. The connections
between the hubs and the computers are made using patch cables having
the same sequence of leads in the RJ45 connectors at each end. For
making a direct connection between two computers without using a hub or
switch, a ‘crossover cable’ is used.

Such a cable has the leads cross-linked in order to allow the two
computers to directly communicate with each other. If there are problems
with the network, it can be handy to be able to directly interconnect
two computers, or directly connect a computer to a cable or ADSL
modem without using a hub or switch. A long crossover cable is not
always available, and shoving around computers is not an attractive
alternative. Consequently, we can use a dual RJ45 wall outlet box to
construct an adapter, which can be used to interconnect the two patch
cables coming from the equipment in question. This outlet box must be
wired to create a cross-linked connection. This is done by making the
following internal connections:

  • 1 → 3
  • 2 → 6
  • 3 → 1
  • 4 → 4
  • 5 → 5
  • 6 → 2
  • 7 → 7
  • 8 → 8

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