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aurora 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.