WAN Hardware

Back in Chapter 6 I discussed the difference between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE). You should recall that DTE equipment is usually the source or destination of a network communication session, such as a router, computer, or terminal. In order for DTE equipment to establish communication over a service provider’s data communications network, DCE equipment is required. Common examples of DCE equipment include:

Modems. A modem provides the ability to connect a DTE device to a service provider’s analog communications facilities. It does this by modulating the digital signal output by a DTE device into the analog signals used on the local loop portion of the Public Switched Telephone Network (PSTN). At the receiving end, a modem demodulates the analog signal back to its digital form. While modems can be used to form a WAN connection between locations, they are typically relegated to “backup duty” because of their relatively slow (56K or less) connection speeds.

Terminal Adapters. A terminal adapter is used in ISDN communications to connect a DTE device to a service provider’s ISDN network. Terminal adapters are similar in function to a modem, in that they are used to dial into a network. However, they do not convert digital signals to analog or vice versa, since an ISDN networks are completely digital.

CSU/DSUs. Channel Service Unit / Data Service Units are the modem-like devices that act as an intermediary between DTE equipment (such as a router) and the service provider’s digital circuit. The CSU/DSU handles the sending and receiving of data over the service provider’s circuit, as well as clocking functions.

Author: Dan DiNicolo

Dan DiNicolo is a freelance author, consultant, trainer, and the managing editor of 2000Trainers.com. He is the author of the CCNA Study Guide found on this site, as well as many books including the PC Magazine titles Windows XP Security Solutions and Windows Vista Security Solutions. Click here to contact Dan.