Uplink Switches, Crossover Cables, And Mdi/Mdix Switching - NETGEAR RangeMax WPN824 Reference Manual

Reference Manual for the RangeMax Wireless Router WPN824
Figure B-6: Category 5 UTP Cable with Male RJ-45 Plug at Each End
Note: Flat "silver satin" telephone cable may have the same RJ-45 plug. However, using telephone
cable results in excessive collisions, causing the attached port to be partitioned or disconnected
from the network.

Uplink Switches, Crossover Cables, and MDI/MDIX Switching

In the wiring table above, the concept of transmit and receive are from the perspective of the
computer, which is wired as Media Dependant Interface (MDI). In this wiring, the computer
transmits on pins 1 and 2. At the hub, the perspective is reversed, and the hub receives on pins 1
and 2. This wiring is referred to as Media Dependant Interface - Crossover (MDI-X).
When connecting a computer to a computer, or a hub port to another hub port, the transmit pair
must be exchanged with the receive pair. This exchange is done by one of two mechanisms. Most
hubs provide an Uplink switch which will exchange the pairs on one port, allowing that port to be
connected to another hub using a normal Ethernet cable. The second method is to use a crossover
cable, which is a special cable in which the transmit and receive pairs are exchanged at one of the
two cable connectors. Crossover cables are often unmarked as such, and must be identified by
comparing the two connectors. Since the cable connectors are clear plastic, it is easy to place them
side by side and view the order of the wire colors on each. On a straight-through cable, the color
order will be the same on both connectors. On a crossover cable, the orange and green pairs will be
exchanged from one connector to the other.
B-14 Network, Routing, Firewall, and Basics
202-10072-01, March 2005