HP ProCurve 7000dl Series Basic Management And Configuration Manual page 444

Configuring Demand Routing for Primary ISDN Modules
Overview of ISDN Connections
TE1
(Router)
Terminal
TE2
adapter
R
interface
8-6
Because public carrier networks were originally designed to carry analog
voice calls, copper wire is the most common physical transmission medium
used on the local loop. Copper wire has a limited signal-carrying capacity,
making local loops that use copper wire the slowest, least capable component
of a WAN connection. ISDN, like DSL, was designed to maximize the limited
capability of local loop copper wiring.
ISDN provides integrated voice and data services by means of a fully digital
local loop. ISDN is a local-loop-only technology. When ISDN traffic reaches
the public carrier's nearest CO, it is converted for transport through the
existing public carrier infrastructure.
On the local loop, ISDN requires at least Category 3 (CAT 3) unshielded twisted
pair (UTP) cabling. The number of wires required depends on the ISDN
service: ISDN BRI requires two wires, or one twisted pair. PRI ISDN requires
four wires, or two twisted pairs.
The local loop is divided into two sections by a line of demarcation (demarc),
which separates your company's wiring and equipment from the public car-
rier's wiring and equipment. (See Figure 8-2.) As a general rule, your company
owns, operates, and maintains the wiring and equipment on its side of the
demarc, and the public carrier owns, operates, and maintains the wiring and
equipment on its side of the demarc. For ISDN connections, the position of
the demarc varies, depending on which ISDN equipment the public carrier
provides.
Demarc (outside
North America)
NT2 NT1
S T
interface interface
Figure 8-2. ISDN Network
Demarc
(North America)
Network
Interface Unit
(Smart Jack)
U
interface
Public
Wire span
Carrier's CO
ISDN
Repeater
Switch