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Reference Manual for the Model RP614 v2 Web Safe Router
Networks, Routing, and Firewall Basics B-13
Ethernet Cabling
Although Ethernet networks originally used thick or thin coaxial cable, most installations currently
use unshielded twisted pair
(UTP) cabling. The UTP cable contains eight conductors, arranged in
four twisted pairs, and terminated with an RJ45 type connector. A normal straight-through UTP
Ethernet cable follows the EIA568B standard wiring as described in Table 6-1.
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 PC,
which is wired as Media Dependant Interface
(MDI). In this wiring, the PC 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 PC to a PC, 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 blue pairs will be
exchanged from one connector to the other.
Table 6-1. UTP Ethernet cable wiring, straight-through
Pin Wire color Signal
1 Orange/White Transmit (Tx) +
2 Orange Transmit (Tx) -
3 Green/White Receive (Rx) +
4Blue
5 Blue/White
6 Green Receive (Rx) -
7 Brown/White
8Brown