Telenetics Corporation FT100 S, Installation And Operation Manual

Page: 121 / 134

FT 100S C-1
Appendix C
T1 Overview
GENERAL
T1 refers to the primary digital telephone carrier system used in North
America. T1 is one line type of the PCM T-carrier hierarchy listed in
Table C-1. T1 describes the cabling, signal type, and signal regeneration
requirements of the carrier system.
T1 was first installed in the early 1960s and was used only to carry voice
trunks between central offices. Since then, T1 facilities have been
provided by telephone companies to customers who need many outside
lines. Since a T1 line supports up to 24 simultaneous voice and / or data
calls, a large savings in both cable and service cost can be realized by
replacing many individual local loops with a single T1 link to the
Central Office. In addition to telephone-company provided T1 services,
many private T1 networks have been implemented such as LAN gate-
ways and PBX-to-PBX links.
The signal transmitted on a T1 line, referred to as the DS1 signal,
consists of serial bits transmitted at the rate of 1.544 Mbps. The type of
line code used is called Alternate Mark Inversion (AMI).
The AMI line code is produced by transmitting a pulse for logic one
data bits and no pulse for logic zero data bits. The signal is called AMI
because pulses alternate in polarity for each logic one bit. If the first one
bit in a bit stream is a + 3V pulse, the next one bit will be a - 3V pulse on
the T1 line.
Table C-1. PCM T-Carrier Hierarchy
Line Signal Line Rate
Number of TDM
Channels
T1 DS-1 1.544 Mbps 24
T1C DS-1C 3.152 Mbps 48
T2 DS-2 6.312 Mbps 96
T3 DS-3 44.736 Mbps 672
T4 DS-4 274.176 Mbps 4032