ISDN Line Simulator User’s Manual
40-400-00012, Rev. E
39
GLOSSARY
5ESS
Medium-to-Large digital end office switch (Class 5). Manufactured by AT&T and
introduced in 1981. First AT&T switch to offer Basic Interface ISDN (with the software
load 5E4.2) in the 1980’s.
AMI (Alternate Mark Inversion)
A Layer 1 line-code scheme used in T1 carrier and ISDN PRI. Zeros are expressed
as no volts, and ones are expressed as volts that alternate polarity. AMI was also the
foundation for proprietary (Pre-National ISDN) BRI line codes for outside wire, which
were limited to distances of about 10,000 feet from the source of the signal.
ASI (Alternate Space Inversion)
A Layer 1 line code specified by the ITU-T for the BRI S/T (inside wire) interface. In
ASI, ones are represented by no volts and zeros are expressed as volts which
alternate polarity. The beginning and end of each frame is denoted by bipolar
violations. Each frame is 48 bits in length. This type of line code is also known as
pseudo-ternary signaling.
Analog Signal
Continuously varying with an amplitude which is an analog of the original information,
amplitude and thus may have virtually an infinite number of states. Contrasted with a
digital signal which has only a very limited number of discrete states.
Analog Transmission
The transmission of a continuously variable signal. Signals are sent through a
system, and where the signal strength weakens, repeaters are installed to amplify the
signal. However, since in an analog transmission there is no way to differentiate
between the :signal and “noise”, repeaters amplify both, and noise becomes
cumulative in an analog transmission system.
ANI (Automatic Number Identification)
The billing number of the calling party. Provided by the originating switch to the
interexchange carrier over equal access trunks (FG-D) for billing.
ANI is also sold by IECs to their direct connect customers, normally in conjunction
with ISDN PRI.
ANSI (American National Standards Institute)
A U.S. organization which is chartered to “accredit” standards developed by a wide
variety of industry groups without undue influence from any one company. ANSI does
not itself develop any standards but accredits those developed by appropriate
organizations. For example, ANSI accredits standards for telephone developed by
ATIS (Alliance for Telecommunications Industry Solutions) under the auspices of
Committee T1, standards for cellular radio developed by EIA/TIA (Electronic
Association), etc.
Application Layers
Open Systems Interconnect (OSI) reference model top layer - layer seven. This end
user layer sets up logical connections for the passing of Application Service Elements
(ASEs) requests and responses between communicating entities.
ASCII (American Standard Code for Information)
A standard governing the representation of various characters as a sequence of
binary digits. Primarily refers to text in personal computers.