noob question on csu/dsu

A4B6

Hi all, Im new to this forum and to CCNA and I am currently studying the CCNA Intro Cisco Press Book. Im stumped at an explaination given on the q&a section for the following question and I was wondering if someone can clear my confusion.

Define the term DCE and DTE in the context of the physical layer and a point to point serial link.

The part of the explaination given on the appendix I'm confused about is as follows:

At the data link layer, both X.25 and Frame Relay define a logical DTE and DCE. In this case, the CPE, such as a router and a CSU/DSU, is the logical DTE, and the service provider equipment (the Frame Relay switch and the CSU/DSU) is the DCE.

Is this explaination saying that the CSU/DSU is both a DTE and a DCE, is this an incorrect assumption?

Thanks for the input!

Netstudent

No a csu/dsu is a DTE. DCE provides clocking on the line which is usually done at the service providor's equipment.

ah damn man you sunk my battleship.

A4B6

Thanks for the quick response. So why did they include CSU/DSU being the service providers equipment and that it is a DCE in the explaination? Thanks again =]

Netstudent

A CSU/DSU interfaces directly with the DCE. The CSU/DSU is kinda like an extension of the DTE. It provides the digital signaling and line encoding used to send data across a digital carrier. But the service providor provides the clocking. The clocking is what constitutes the throughput or bit rate of the line.

Most modern gear doesn't use external CSU/DSU anymore anyways. Most of the time the DSU component is integrated into the WAN card of the router. Then a cat5e cable runs to a Smart Jack. I'm not saying don;t learn about CSU/DSU's but they arn;t aprt of the ccna test and they are kinda phasing out of the industry I think.

A4B6

Cool, that makes sense. thanks