Physically Connecting a WAN Interface

The WAN Physical layer describes the interface between the data terminal equipment (DTE) and the data circuit-terminating equipment (DCE). Generally, the DCE is the service provider and the DTE is the attached device. In this model, the services offered to the DTE are made available either through a modem or a CSU/DSU.

Typically, the router is the DTE device and is connected to a CSU/DSU, which is the DCE device. The CSU/DSU (DCE device) is used to convert the data from the router (DTE device) into a form acceptable to the WAN service provider. The CSU/DSU (DCE device) is also responsible for converting the data from the WAN service provider into a form acceptable by the router (DTE device). The router is usually connected to the CSU/DSU using a serial DTE cable, as shown.

Serial interfaces require a clock signal to control the timing of the communications. In most environments, the service provider (a DCE device such as a CSU/DSU) will provide the clock. By default, Cisco routers are DTE devices. However, in a lab environment, we are not using any CSU/DSUs and, of course, we do not have a WAN service provider.(more information)

Ethernet Connector

A different connector is used in an Ethernet-based LAN environment. An RJ-45 connector for the unshielded twisted-pair (UTP) cable is the most common connector used to connect LAN interfaces. At each end of an RJ-45 cable, you should be able to see eight colored strips, or pins. An Ethernet cable uses pins 1, 2, 3, and 6 for transmitting and receiving data.

Two types of cables ..

can be used with Ethernet LAN interfaces:

• A straight-through, or patch cable, with the order of the colored pins the same on each end of the cable
• A crossover cable, with pin 1 connected to pin 3, and pin 2 connected to pin 6

Straight-through cables are used for:

• Switch-to-router
• Switch-to-PC
• Hub-to-PC
• Hub-to-server

Crossover cables are used for:

• Switch-to-switch
• PC-to-PC
• Switch-to-hub
• Hub-to-hub
• Router-to-router
• Router-to-server

Connection for WAN

For WAN connections, Cisco routers support the EIA/TIA-232, EIA/TIA-449, V.35, X.21, and EIA/TIA-530 standards for serial connections, as shown. Memorizing these connection types is not important. Just know that a router has a DB-60 port that can support five different cabling standards. Because five different cable types are supported with

this port, the port is sometimes called a five-in-one serial port. The other end of the serial cable is fitted with a connector that is appropriate to one of the five possible standards.(more information)