CCNA Cisco Certified Network Associate Study Guide - FTP Server

Assembling and Cabling Cisco Devices 43
Serial links are described in frequency or cycles-per-second (hertz). The
amount of data that can be carried within these frequencies is called bandwidth.
Bandwidth is the amount of data in bits-per-second that the serial
channel can carry.
Data Terminal Equipment and Data
Communication Equipment
Router interfaces are, by default, Data Terminal Equipment (DTE) and connect
into Data Communication Equipment (DCE), for example, a Channel
Service Unit/Data Service Unit (CSU/DSU). The CSU/DSU then plugs into a
demarcation location (demarc) and is the service provider’s last responsibility.
Typically, the demarc is a jack that has an RJ-45 female connector
located close to your equipment. If you report a problem to your service provider,
they’ll always tell you it tests fine up to the demarc and that the problem
must be the CPE, or Customer Premise Equipment, which is your
responsibility.
The idea behind a WAN is to be able to connect two DTE networks
together through a DCE network. The DCE network includes the CSU/DSU,
through the provider’s wiring and switches, all the way to the CSU/DSU
at the other end. The network’s DCE device provides clocking to the DTEconnected
interface (the router’s serial interface).
Fixed and Modular Interfaces
Some routers Cisco sells have fixed interfaces, while others are modular. The
fixed routers, such as the 2500 series, have set interfaces that can’t be
changed. The 2501 router has two serial connections and one 10BaseT AUI
interface. If you need to add a third serial interface, then you need to buy a
new router—ouch! However, the 1600, 1700, 2600, 3600, and higher routers
have modular interfaces that allow you to buy what you need now and
add almost any type of interface you may need later. The 1600 and 1700 are
limited and have both fixed and modular ports, but the 2600 and up provide
many serials, FastEthernet, and even voice-module availability.
Integrated Services Digital Network (ISDN) Connections
Integrated Services Digital Network (ISDN) Basic Rate Interface (BRI) is
two B (Bearer) channels of 64k each and one D (Data) channel of 16k for signaling
and clocking.