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Chapter 1
T1/FT1 OVERVIEW
T1 Service Offerings
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Introduction
T1 digital communication links have been used by the
transmitting companies (Telcos) for the transmitting of voice
since the early sixties. The D4 channel bank is an example of
a T1 digital carrier system that was introduced in the mid
seventies and is still widely used by the Telcos.
Communication demands of businesses continued to grow to
the point that the Telcos began offering T1 service directly to
the public. D4 channel banks began to be used for T1 in
corporate network topographies for voice. The technological
advances in computer development created a demand also
for T1 data communication which now is a large part of the
T1 traffic.
T1 is a digital service that is delivered to the user over two
pairs of wires from the service provider. The signal operates
at 1.544Mbps and is usually extended by repeaters that are
installed about every mile after the first 6000 feet. The T1
signal is divided into 24 time slots which operate at 64 kbps
(DS0s). Each time slot is occupied by digitized voice or by
data.
The T1 signal originally used a type of framing known as D4
Superframe which identifies how the T1 is multiplexed. An
enhancement of that framing format is available now called
Extended Superframe (ESF). ESF provides a non-disruptive
means of full time monitoring on the digital facility. It was
originally used by the service provider to monitor the
TSU User Manual
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