ADTRAN TSU 610 User Manual page 157

Appendix F
HDSL TECHNOLOGY OVERVIEW
61200610L2-1
HDSL Deployment Guidelines
Typically, T1 circuits are deployed from a telephone company
office using a device known as an office repeater. See Figure
F-1 on page F-3. If the circuit termination point is farther than
3,000 feet from the serving office, a T1 loop repeater is
generally installed to recover and regenerate the signal before
the loop attenuation encountered renders the signal
unusable. Subsequent spacing of loop repeaters is
approximately 6,000 feet.
The T1 line is then terminated on the customer premises with
a T1 Channel Service Unit (CSU). In some places, such as a
dense metropolitan area, providing an acceptable location for
a loop repeater can become expensive. As a consequence of
deploying loop repeaters, a portion of telephone company
equipment is no longer located in the Central Office (CO) and
therefore requires additional expense in servicing and
maintaining the circuit. The HDSL concept is to enhance the
transmission scheme for T1 signals such that a complete
Carrier Service Area (CSA) can be addressed without the
need for a loop repeater or conditioned local loops.
A CSA varies depending on wire gauge, but extends roughly
9,000 to 12,000 feet from a serving office. Also, total bridged
tap lengths of up to 2,500 feet are permissible with single
bridged tap lengths not exceeding 2,000 feet.
The existing T1 transmission scheme is Alternate Mark
Inversion (AMI) resulting in a power spectrum centered
around 7772 kHz. Attentuation (loss), crosstalk, and other
undesirable effects of transmitting information over twisted
pair cables increase as the frequency of the power spectrum
increases.
TSU 610 User Manual F-1