ADTRAN Express L1.5, User Manual

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61202192L1-1 Express L768/L1.5 User Manual 13
Chapter 2
Installation
After unpacking the unit, immediately inspect it for possible shipping dam-
age. If damage is discovered, file a claim immediately with the shipping car-
rier; then contact the ADTRAN Customer and Product Service (CAPS)
department (see inside back cover for information).
HDSL NETWORK CONNECTION
T1 Overview
The T1 digital communications link has been used by telephone companies
(telcos) for transmitting voice since the early sixties. The D4 channel bank is a
T1 digital carrier system that was introduced in the mid-seventies and is still
widely used by telcos. Communication demands of businesses continued to
grow to the point that the telcos began offering T1 service directly to the pub-
lic. D4 channel banks began to be used for T1 in corporate network topogra-
phies for voice. The advances in computer development also created a
demand 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 1.544 Mbps and is usually extend-
ed by repeaters that are installed about every mile after the first 6000 feet. The
T1 signal is divided into 24 time slots (DS0s) which operate at 64 kbps. Each
time slot is occupied by digitized voice or by data.
HDSL Overview
T1 service traditionally has been delivered from the service provider with an
office repeater over metallic facilities with an alternate mark inversion (AMI)
scheme. If the customer is beyond 3000 feet, a T1 loop repeater is used with ad-
ditional repeaters spaced at 6000 feet.