1993 << Back To The X Files nº 3

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