HP ProCurve Secure 7000dl Series Basic Management And Configuration Manual page 191

Router (DTE)
LAN
Figure 4-2. Local Loop
All carrier lines require the same basic components on the local loop, although
the components may differ slightly in form and design. (See Figure 4-2.) These
components are listed below:
CSU/DSU—The Channel Service Unit/Digital Service Unit (CSU/DSU) has
two purposes: The DSU accepts traffic from the router and translates it
from the signaling format used on the LAN to the format necessary for
transmission on the WAN. The CSU then generates the signal to be sent
across the WAN. For incoming traffic, the CSU regenerates the signal for
transmission across the LAN.
Demarc—A line of demarcation, or demarc, separates your wiring and
equipment from the public carrier's wiring and equipment. As a general
rule, you own, operate, and maintain the wiring and equipment on your
side of the demarc, and the public carrier owns, operates, and maintains
the wiring and equipment on its side of the demarc.
Network interface unit (NIU)—The NIU automatically maintains the WAN
connection and enables public carrier employees to perform simple man-
agement tasks from a remote location. The NIU is usually located outside
the subscriber's premises so that public carrier employees can always
access it. In the United States and Canada, the NIU is commonly referred
to as the smart jack.
Wire span—Because public carrier networks were originally designed to
carry analog voice calls, copper wire is still the most common physical
transmission medium used on the local loop. Because copper wire has a
limited capacity to carry signals, local loops that use copper wire are the
slowest, least capable component of the WAN connection.
Configuring E1 and T1 Interfaces
Overview of E1 and T1 WAN Connections
Network
CSU/
Interface Unit
DSU
(Smart Jack)
Demarc
Wire span
Repeater
OCU
Public
Carrier's CO
Office Channel Unit
(PTT's CSU)
4-5