Specifications

Chapter A Networking Concepts
WAN Technologies
A-2
Cisco 1700 Series Router Software Configuration Guide
78-5407-03
ISDN
ISDN is a set of digital services that is available through your local telephone
company. ISDN digitizes information that is sent over the telephone network so
that voice, data, text, graphics, music, video, and other material can be sent over
existing telephone wire.
ISDN Components
ISDN components include terminals, terminal adapters (TAs), network
termination devices, line-termination equipment, and exchange-termination
equipment.
ISDN Terminals
There are two type of ISDN terminals:
• Terminal equipment type 1 (TE1) is designed specifically to work with ISDN.
TE1s connect to the ISDN network with 4-wire, twisted-pair cable.
• Terminal equipment type 2 (TE2) is non-ISDN equipment (such as data
terminal equipment [DTE]) that predates ISDN standards. TE2s connect to
the ISDN network with a terminal adapter.
ISDN Network Termination Devices
Two types of ISDN terminal devices can connect your router to the telephone
company’s conventional 2-wire local loop:
• Network termination type 1 (NT1)—In North America, the NT1 is provided
by the customer. In most other parts of the world, the NT1 is part of the
network provided by the ISDN service provider. WAN interface cards that do
not have an integrated NT1 must have an external NT1 in order to connect to
ISDN services. The Cisco 1604 and ISDN BRI U WAN interface cards each
have an integrated NT1.
• Network termination type 2 (NT2)—This more complicated device is usually
found in digital private branch exchanges (PBXs).
There is also an NT1/2 device available that can perform the functions of both an
NT1 and an NT2.