HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual page 88

Configuring Backup WAN Connections
Backing Up Primary WAN Connections
3-8
Wire span—Because public carrier networks were originally designed to
carry analog voice calls, copper wire is the most common physical trans-
mission medium used on the local loop. Although copper wire has a limited
signal-carrying capacity, ISDN is designed to maximize its capability.
Network Interface Unit (NIU)—The NIU automatically maintains the
WAN connection and enables public carrier employees to perform simple
management tasks from a remote location. The NIU is usually located
outside the subscriber's premises so that public carrier employees can
always access it. (The NIU is commonly referred to as the "smart jack" in
North America.)
Network Termination (NT) 1—The NT1 provides the physical and electri-
cal termination for the ISDN line. It monitors the line, maintains timing,
and provides power to the ISDN line. In Europe and Asia, public carriers
supply the NT1. In North America, however, the subscriber provides the
NT1. In fact, many ISDN vendors are now building the NT1 directly into
ISDN equipment such as routers.
NT 2—PRI ISDN also requires an NT2, which provides switching functions
and data concentration for managing traffic across multiple B channels.
In many regions, the NT1 and NT2 are combined into a single device,
which is called an NT12 (NT-one-two) or just NT.
Terminal equipment (TE) 1—TE1 devices are ISDN-ready devices and can
be connected directly to the NT1 or the NT2. TE1 devices include routers,
digital phones, and digital fax machines.
TE2—TE2 devices do not support ISDN and cannot connect directly to
an ISDN network. TE2 devices require a terminal adapter (TA) to convert
the analog signals produced by the TE2 device into digital signals that can
be transmitted over an ISDN connection. TE2 devices include analog
telephones and analog fax machines.
Terminal adapter (TA)—A TA allows you to connect a TE2 device to an
ISDN network.
You do not need to understand all of the equipment used to create the local
loop with great technical precision. However, if your ISDN line ever goes
down, a basic knowledge and working vocabulary can help you troubleshoot
problems with your public carrier.
You should also understand that the demarc defines which equipment your
organization is responsible for maintaining. In addition, the demarc deter-
mines the type of ISDN backup module you use, as explained in the next
section.