hdsl_tn - HDSL Basics 1 HDSL Basics Introduction Providing...

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1 HDSL Basics HDSL Basics Introduction Providing T1 service is a competitive race, and High-bit-rate Digital Subscriber Line (HDSL) is quickly emerging as the ideal solution to remain a step ahead. Currently touted as “repeaterless T1”, HDSL enables T1 service to travel up to 12,000 ft. on copper cable with- out regeneration. When used with a single HDSL doubler, service can be extended to 24,000 ft. By elimi- nating T1 line repeaters and fault locate pairs, HDSL can provide service in as little as 24 hours over two existing POTS lines. This enables established service providers to meet the demands for quicker turn-ups and impro- ved service quality over the installed base of copper cable. The increase in efficiency comes without sacrific- ing service quality as HDSL features several enhance- ments that eliminate the common problems associated with standard T1 transmission. HDSL enables establish- ed service providers to remain competitive while re- ducing operational costs. This Technical Note provides an overview of HDSL technology, a detailed discussion of how HDSL works, and recommended test procedures that can guarantee consistent performance. HDSL Overview The standard HDSL loop architecture, shown in Figure 1A , is a point-to-point circuit that consists of two HDSL transmission units (HTUs). The HTU-C [HTU at the central office (CO)] replaces the T1 office repeat- er and fits easily into any standard 220 office repeater bay. The HTU-R (remote HTU) can be installed with, or replace, the network interface unit (NIU) at the customer demarcation point. The HTUs are then connected by two non-loaded copper cable pairs. If the local loop exceeds 12,000 ft., a HDSL doubler can be installed, as shown in Figure 1B , on the next page, to extend service up to 24,000 ft. HDSL Loop 1 DSX-1 HTU-C HTU-R MDF HDSL Loop 2 NIU/CPE Central Office Customer Premise Figure 1A Point-to-point circuit.
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2 HDSL Basics Figure 1B Extending service with a HDSL doubler. Under normal operation, the HTU-C receives a standard T1 signal on Side 1 from the DSX-1. The HTU-C derives timing and converts the T1 into two HDSL sig- nals, each representing half the T1 bandwidth. The HDSL signals are then transmitted on Loop 1 and Loop 2. The HTU-R receives the HDSL signals, reconverts them to a single T1 signal, and sends it to the customer on Side 1. The process is then reversed on Side 2, toward the CO. The HTU-R receives a standard T1 on Side 2 from the channel service unit (CSU) at the customer premises. It derives timing and converts the T1 into two HDSL sig- nals, each representing half the T1 bandwidth. The HDSL signals are then transmitted on both loops. The HTU-C receives the signals, reconverts them to a single T1 signal, and sends it to the DSX-1 on Side 2. In order to transmit and receive on the same pair, the HTUs utilize transceivers rather than the separate transmitter and receiver used by standard T1 equipment. Figure 2 depicts this process.
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This note was uploaded on 08/08/2011 for the course CS 310 taught by Professor Aartisingh during the Spring '11 term at National Institute of Technology, Calicut.

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hdsl_tn - HDSL Basics 1 HDSL Basics Introduction Providing...

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