External Or Built-In Csu/Dsu - HP ProCurve 7000dl Series Basic Management And Configuration Manual

Configuring E1 and T1 Interfaces
Overview of E1 and T1 WAN Connections
4-6
Repeater—A repeater receives, amplifies, and retransmits the digital
signal so that the signal is always strong enough to be read. The distance
between repeaters depends on the type of connection, including the
transmission media used. On an E1 or T1 connection over unshielded
twisted pair (UTP) wiring, the distance between repeaters is one mile
or less.
Office channel unit—Located at the CO, the office channel unit (OCU)
performs the same function at the public carrier's site that the CSU
performs at each subscriber's site: It generates the signal to be sent across
the WAN—either to be sent to a subscriber's premises or to be transmitted
on to the public carrier network.
Although you will never see most of these components, having a basic under-
standing of the local loop can help you work with your public carrier to
troubleshoot problems if your E1- or T1-carrier line ever goes down.
In addition, two of these components directly affect your E1 or T1 WAN
connection: the demarc and the CSU/DSU. The demarc determines which part
of the E1 or T1 WAN connection you are responsible for. Again, this becomes
important if your E1- or T1-carrier line ever goes down and you have to work
with the public carrier to identify and fix the problem.
The CSU/DSU is important because its form and design not only determines
which ProCurve Secure Router module you purchase but also which settings
you must configure for the E1- or T1-carrier line.

External or Built-in CSU/DSU

Your public carrier determines the type of CSU/DSU that will be used in your
WAN connection. There are three options:
The public carrier provides the CSU/DSU and installs it on your premises.
The public carrier provides the CSU but not the DSU.
The public carrier does not provide the CSU/DSU.
In Europe, Australia, South America, and Asia (except Japan), the PTT author-
ity will provide both the CSU/DSU or just the CSU. In the United States and
Canada, public carriers will either provide the entire CSU/DSU, or they will
not provide either one at all.
If the public carrier provides an external CSU/DSU, you should purchase a
serial module. (See Figure 4-3.) For information about the serial module, see
Chapter 5: Configuring Serial Interfaces for E1- and T1-Carrier Lines.