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Twisted Pair Cables
For two devices to communicate, the transmitter of each device must be connected to the receiver
of the other device. The crossover function is usually implemented internally as part of the
circuitry in the device. Most ports on hubs and repeaters have media-dependent interfaces with
crossover ports. These ports are referred to as MDI-X or normal ports. Computer and workstation
adapter cards are usually media-dependent interface ports referred to as MDI or uplink ports.
These two figures illustrate the use of straight-through and crossover twisted pair cables.
Uplink or
MDI port
Normal or
MDI-X port
RJ-45 Connector
The RJ-45 connector (shown in the illustration with an RJ-45 plug) is used to connect
workstations and hubs through unshielded twisted pair cable. The RJ-45 connector accepts four-
pair Category 3 or Category 5 UTP cable. Only two pairs are used for 10BASE-T wiring.
RJ-45
Connector
Normal Assignment:
Pin Assignment
1
Input Receive Data +
2
Input Receive Data -
3
Output Transmit Data +
6
Output Transmit Data -
4,5,7,8
Not used
Model DS309 Dual Speed Hub Installation Guide
Straight-through
twisted pair cable
1
Tx
2
3
Rx
6
Crossover
twisted pair cable
1
Rx
2
3
Tx
6
12345678
Normal or
MDI-X port
1
Rx
2
3
Tx
6
Normal or
MDI-X port
1
Rx
2
3
Tx
6
8146EC
8
1
711EA
Uplink Assignment: Port 9 on the
Model DS309 Hub
Output Transmit Data +
Output Transmit Data -
Input Receive Data +
Input Receive Data -
Not used
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