ISDN Demonstrator User’s Manual
40-400-00011, Rev. B
39
Loop
Pair of wires connecting the subscriber to the Telephone Company central office.
Modem (Modulator/Demodulator)
A device which converts data signals into a form suitable for transmission over a
communications medium and which recovers the data from the received
communication link. This term is a contraction of MOdulator/DEModulator.
“Voiceband” Modems are a special class of Modems which convert data signals into
TONES within the bandwidth allocated for voice. Direct Digital Interfaces are another
class of modems which convert data into the format needed for transmission over
digital radio channel.
MPEG (Motion Picture Experts Group)
the emerging ISO standard for the compression and coding of motion video. Also, the
name of the standards group developing the standard.
There are three versions of MPEG:
MPEG-1
operates up to about 2.5 Mb/s and is suitable for storage on digital storage
media, e.g. hard disks, CD-ROMs, etc.
MPEG-2
operates at higher bit rates for broadcast-quality video
MPEG-4,
still underdevelopment, will standardize video compression for video
conferencing on analog phone calls.
N-ISDN (Narrowband ISDN)
Narrowband Integrated Services Digital Network. Includes basic interface (2B+D or
BRI) and primary rate interface (23B+D or PRI). Copper based at speeds at or below
1.5 Mb/s.
NT1 (Network Termination 1)
In the U.S., a customer-owned device that converts from external telephone company
transmission format (U interface) to internal building transmission format (T interface).
Concerned only with Layer 1. Should contain loopback and other maintenance
capabilities to enable problems to be isolated to the telephone network or customer’s
equipment. NT1 for basic interface contains digital hybrid circuitry.
NT2 (Network Termination 1 and 2)
Customer premises device to fan out a user-to-network (T) interface into multiple T or
R interfaces. Concerned with Layer 1, 2, and 3. Examples are a PBX, Key system,
LAN, and terminal controller.
OSI (Open System Interconnection Reference Model)
Open Systems Interconnection. The International Standards Organization (ISO)
model of how data communications systems can be interconnected. Communication
is partitioned into seven functional layers. Each layer uses and builds on the services
provided by those below it.
Out-of-Band Signaling
A system that uses a separate communications channel or frequencies outside of
voice band for signaling. Digital examples are the ISDN D channel and common
channel signaling.
