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Sonata
Hand Held ISDN Tester—User Guide
A4-8 427869
Noise An unwanted signal.
Nortel The proprietary ISDN protocol for use with the DMS
family of products.
NT Network Termination.
NT1 An NT on the customer's premises, providing a physical
and electromagnetic termination of the network. The
transmission line (U interface) is terminated by NT1.
NT2 The Customer Premises Equipment (CPE), with a T
reference point on the network side. For example, an
ISDN PABX.
Octet A digital unit of information consisting of 8 bits.
Off hook A line state which informs the Central Office that a
subscriber requires a service.
On hook The unused state of a telephone circuit.
OSI 7-layer A model defined by the ISO, in which ISDN functions
Model are separated into 7 clearly defined layers.
Overlap A type of dialling where the digits are sent one at a time,
each in its own separate call control packet.
PABX Private Automatic Branch Exchange. Consists of a number
of ‘extension lines’ connected to a central switching
system. Users on these extensions can make calls to each
other. ‘Exchange lines’ connect the PABX to the local
public exchange, allowing the extension users access to the
Public Switched Telephone Network (PSTN).
Packet A transmission method in which data is formed into
switching discrete segments known as packets. A packet usually has
its own control information. Packets occupy a
communication channel for a short duration, so packets
from several users can share a channel.
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