Analog Interfaces, Intelligent Networks, DNHR
Analog Interfaces, Intelligent Networks, DNHR Lecture (7) Analog Interfaces • The design, implementation and maintenance of any large and complex system require partitioning of the system into subsystems. • Associated with each subsystem is an interface that defines the inputs and outputs independent of internal implementations. • Well established interfaces are fundamental requirements to maintain compatibility between old and new equipment. 1 Principal Analog Interfaces: • Subscriber Loop interface • Loop-Start Trunks • Ground Start Trunks • Direct-Inward-Dial Trunks • E&M trunks Subscriber Loop Interface • The most common interface involves 2- wire connection of individual telephone lines to end office switches. • Fundamental characteristics of this interface are: BORSCHT • Per-line SLIC s allow implementation of per-line BORSCHT functions. SLIC : Subscriber Loop Interface Circuit 2 BORSCHT • Battery Feed: 48V normally • Over-voltage Protection • Ringing: 20Hz, 86 V rms, 2 sec ON & 4 sec OFF. • Supervision: Detection of ON-Hook or Off-Hook • Coding *: A/D or D/A • Hybrid *: 2- to 4- wire conversion • Test: Access to line test in either direction. * Digital Switch Interface Requirements LS Trunks • Loop start circuit is monitored based on its DC current status for signals and on- and off-hook conditions. • Loop Start lines have immediate dial tone. • 24 × 7. • Less expensive, easy deployment. • Residential, Small and Medium Business Services. 3 Loop-Start Trunks • The two wires in the phone line (tip and ring) are bridged (shorted) together through a resistor (say 1K) when the handset is taken off-hook. • The CO detects the current in the loop. • By operational point of view, identical to SLI. Drawback • With 2-way LS trunks, difficulty arises when both ends of the line seize the line at the same time – ‘glare’ situation.
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