Ccna routing and Switching Complete Study Guide

Data Terminal Equipment and Data Communication 

Equipment

By default, router interfaces are typically data terminal equipment (DTE), and they connect 

into data communication equipment (DCE) like a channel service unit/data service unit 

(CSU/DSU) using a V.35 connector. CSU/DSU then plugs into a demarcation location 

(demarc) and is the service provider’s last responsibility. Most of the time, the demarc is a jack 

that has an RJ45 (8-pin modular) female connector located in a telecommunications closet.

Actually, you may already have heard of demarcs. If you’ve ever had the glorious 

experience of reporting a problem to your service provider, they’ll usually tell you 

everything tests out fine up to the demarc, so the problem must be the CPE, or customer 

premises equipment. In other words, it’s your problem, not theirs!

Figure 21.9 shows a typical DTE-DCE-DTE connection and the devices used in the network.

f i g u r e   21. 9     DTE-DCE-DTE WAN connection: Clocking is typically provided by the DCE 

network to routers. In nonproduction environments, a DCE network is not always present.

DTE

DTE

DCE