Reference Manual for the Model DG824M Wireless ADSL Modem 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 as described in Table 7-1.

Table 7-1.

UTP Ethernet cable wiring, straight-through

 

 

 

 

Pin

Wire color

Signal

 

 

 

 

 

1

Orange/White

Transmit (Tx) +

 

 

 

 

 

 

2

Orange

 

Transmit (Tx) -

 

 

 

 

 

3

Green/White

Receive (Rx) +

 

 

 

 

 

 

4

Blue

 

 

 

 

 

 

 

5

Blue/White

 

 

 

 

 

 

 

6

Green

 

Receive (Rx) -

 

 

 

 

 

7

Brown/White

 

 

 

 

 

 

 

8

Brown

 

 

 

 

 

 

 

 

Uplink Switches and Crossover Cables

In the wiring table, the concept of transmit and receive are from the perspective of the PC. For example, the PC transmits on pins 1 and 2. At the hub, the perspective is reversed, and the hub receives on pins 1 and 2. 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.

Network and Routing Basics

B-11

Page 119
Image 119
NETGEAR DG824M manual Ethernet Cabling, Uplink Switches and Crossover Cables