120 lines
4.2 KiB
Plaintext
120 lines
4.2 KiB
Plaintext
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\ / |_
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/ \ e n o n | o u n d a t i o n
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presents:
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\ /
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*------ the \ /
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/ \ files ------*
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/ \
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Fall/1993 Issue: 3
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INTRODUCTION TO BASIC DIGITAL TECHNOLOGY
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Written by: Erik Turbo
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File: 3 of 6
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3. Channel Banks
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3.1 Introduction
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In this next section you will learn about a typical digital facility. Most
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digital facilities contain:
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> Channel Banks
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> A Transmission System
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You will learn about the channel banks and a typical transmission system
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which includes:
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> Loop Plant
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- Loop Cables
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- Impairments
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- Digital Loop Carrier (DLC)
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- SCL 96--Modem 3
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3.2 Digital Channel Banks
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> The function of the digital facility is to provide 24 Voice Frequency (VF)
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channels from one point to another over a PCM transmission system. The
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most basic type of digital facility consists of two elements:
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1. Channel Banks (or terminals)
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2. A Transmission System
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> The channel banks provide the A/D interface between 24 VF circuits and a
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digital Pulse Code Modulation (PCM) transmission system. The digital
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transmission signal between two channel banks.
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3.3 Loop Plant
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The loop plant is the connect between the telephone customer and the serving
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Central Office. Most loops are quite short, the median length is about
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1.7 miles.
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1. Loop Cables
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The loop plant gernerally consists of metallic cable pairs. Typical
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cable gauges are the 19, 22, 24, or 26 gauge. The higher the gauge
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number, the smaller the wire diameter and the more resistance per foot.
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CABLE GAUGE OHMS/KFT
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-------------------------------------------------------
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26 83.2
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24 51.9
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22 32.8
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19 16.3
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2. Impairments
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As the distance from the Central Office increases, so does transmission
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loss. Switching systems and telephone equipment are designed to oper-
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ate at specified limits, therefore, the loop plant is generally limited
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without treatment from 1,300 to 1,500 ohms. In addition the resistance,
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another factor that impacts transmission is loop capacitance.
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3. Digital Loop Carrier (DLC)
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The loop capacitance results in greater loss at the higher frequencies.
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To care for this, loop cable over 18 Kft are equipped with load coils.
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New loop cable configurations, longer than 24 Kft, generally used
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Digital Loop Carrer (DLC) such as SLC 96.
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3.4 Digital Loop Carrier (DLC)
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Digital Loop Carrier (DLC) systems are being installed in significant
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numbers, about 50,000 DS1 lines per year, to provide new services and
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reduce cost. The systems in use include AT&T SLC 96 system, Norther
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TELECOM's DMS-1 Urban, and systems from other vendors.
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The SLC 96 system is a digital subscriber carrier system which provides
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up to 96 subscriber lines. It provides residential, coin, and special
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services. SLC 96 operates in three modes with Mode 3 used for special
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service including Digital Data Services (DDS) dataport.
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This SLC 96 layout is similar to Mode 1 and Mode 2 having a Central
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Office (CO) and Remote Terminal (RT). The major difference is that the
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channels are reduced from 24 to 12 for each bank. D4 Channel units can
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be used in the SLC 96 Mode 3 arrangement
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The Mode 3 arrangement has two T1 (DS1) lines plus one T1 for protection
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in case of a line problem on either of the service lines.
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------------------------------------------------------------------------------
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EOF ---------------- Xenon Foundation Productions 1993 -------------------EOF
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------------------------------------------------------------------------------
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