Table of Contents

T-carrier
T-carrier is the generic name for digital multiplexed carrier systems. The letter T
stands for trunk, as these links were originally designed to trunk multiple phone
lines between central offices. The T-carrier hierarchy is used in the US and Canada.
Europe uses a similar scale called the European E-carrier hierarchy, and Japan uses
a system titled the Japanese J-carrier hierarchy. The North American T-carrier hierarchy
is shown in Table 20-5.
Table 20-5. North American T-carrier hierarchy
Designator Transmission rate Voice channels
T1 1.544 Mbps 24
T1C 3.152 Mbps 48
T2 6.312 Mbps 96
T3 44.736 Mbps 672
T4 274.176 Mbps 4,032
T-Berd
A T-Berd is a T1 Bit Error Rate Detector. The generic term is used for any device
that will perform BERT tests on a T1. If you have a T1 that’s misbehaving, the
provider will probably send out an engineer with a T-Berd to perform invasive
testing.
TDM
TDM stands for time-division multiplexing. A T1 link is a TDM link because its
24 channels are divided into time slots. A T1 link is a serial link, so one bit is sent
at a time. The channels are cycled through at a high rate of speed, with each channel
being dedicated to a slice of time.
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