NETGEAR DG814 DSL Ethernet Cabling, Uplink Switches, Crossover Cables, and MDI/MDIX Switching

Reference Manual for the Model DG814 DSL Modem Internet Gateway

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 and pinout as described in Table B-3.

Table B-3.		UTP Ethernet cable wiring, straight-through
Pin	Wire color		Signal
1	Orange/White		Transmit (Tx) +
2	Orange		Transmit (Tx) -
3	Green/White		Receive (Rx) +
4	Blue
5	Blue/White
6	Green		Receive (Rx) -
7	Brown/White
8	Brown

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 Dependent 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 Dependent 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 three mechanisms:

•Uplink switch

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.

Networks and Routing Basics B-11