Ethernet Cable

Description

An Ethernet cable consists of twisted pairs and RJ45 connectors at both ends. Pin assignments in the RJ45 connectors comply with the T568A or T568B standard. Table 8-9 describes the two standards.

Depending on whether RJ45 connectors at both ends comply with the same standard, Ethernet cables are classified into two types:

• Straight-through cable: The RJ45 connectors at both ends comply with the T568B standard.
• Crossover cable: One RJ45 connector complies with the T568A standard, and the other RJ45 connector complies with the T568B standard.

Structure and Pin Assignments

Figure 8-7 shows the structure of an Ethernet cable.

Figure 8-7 Structure of an Ethernet cable

Table 8-10 lists the pin assignments of a straight-through cable.

Table 8-11 lists the pin assignments of a crossover cable.

Connection

A straight-through cable can connect devices at different network layers in the following scenarios:

• Connect a switch or hub to a router.

• Connect a computer (server or workstation) to a switch or hub.

• Connect a switch to an upper-layer switch through an uplink interface.

A crossover cable can connect devices at the same network layer in the following scenarios:

• Connect a computer to a router.

• Connect two switches at the same layer.

• Connect two hubs.

• Connect two computers.

• Connect two routers.

• Connect an Ethernet interface of an ADSL modem to the network interface of a computer.

Most network devices support auto-negotiation on their interfaces. After auto-negotiation is enabled, the local and remote interfaces can automatically negotiate about communication parameters. In this case, the two interfaces can be connected by either a straight-through cable or a crossover cable.

Ordering Information

Select straight-through or crossover cables according to your network requirements. In an environment with severe electromagnetic interference, shielded Ethernet cables are recommended.

Table 8-12 provides the Ethernet cable ordering information.