--- title: "Classification of switching systems" subject: "Telecommunications" chapter: 1 key: "semester_8/telecommunications:classify-switching-systems" source: https://www.bctengineer.com/q/semester_8/telecommunications/classify-switching-systems site: BCT Engineering --- # Classification of switching systems Telecommunications · Chapter 1: Telecommunication Networks - Asked in: 2073 Chaitra, 4+4 marks - Video: [CLASSIFICATION OF SWITCHING SYSTEMS](https://www.youtube.com/watch?v=njx2wXno8ic) — Shalini Sharma - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/telecommunications/classify-switching-systems - Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-1 ## Question Classify various switching systems in telecommunication. Mention functions of digital switching system. ## Short answer Switching systems are manual, electromechanical automatic (Strowger, crossbar), and electronic SPC with space or time division; transfer modes are circuit, message and packet. Digital exchange functions include supervision, digit reception, processing, busy test, interconnection, alerting, call supervision, signalling, release, charging and maintenance. ## Answer #### Classification of switching systems ```text Switching systems / \ Manual Automatic / \ Electromechanical Electronic (SPC) / \ / \ Strowger Crossbar Space Time division (step-by-step) division (digital) (centralised or distributed control) ``` - **Manual:** operator connects calls (local battery, central battery boards). - **Electromechanical automatic:** - **Strowger (step-by-step)** – direct progressive control by dial pulses. - **Crossbar** – common control with markers and registers. - **Electronic (Stored Program Control):** a computer controls switching. - **Space-division** – separate physical path per call (reed relays, crosspoints). - **Time-division** – shared paths with time slots; analogue PAM or **digital PCM** (time and T-S-T switches). - Control can be **centralised** or **distributed**. - By information transfer: **circuit switching**, **message switching** and **packet switching**. #### Functions of a digital switching system 1. **Attending/supervision:** continuously scan lines and trunks to detect off-hook (call request) and on-hook. 2. **Information receiving:** give dial tone and receive dialled digits (pulse or DTMF). 3. **Information processing:** analyse digits, translate the number and decide routing and charging. 4. **Busy testing:** check whether the called line or trunk is free. 5. **Interconnection:** set up a path through the time/space switch network (assign time slots). 6. **Alerting:** ring the called party and send ringback tone to caller. 7. **Supervision during the call:** watch for answer and clear-down; start/stop charging. 8. **Information sending:** signal to other exchanges (CAS/SS7) for outgoing calls. 9. **Disconnection/release** of the path at the end of call. 10. **Charging, maintenance and administration:** billing records, fault detection, traffic statistics, subscriber data changes, and supplementary services (call forwarding, waiting, conference). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is an electromechanical automatic system? A. Space-division reed relay B. Strowger or crossbar C. Time-division PCM D. Softswitch Answer: B. Reed relay and PCM are electronic. (Key point: Classification) 2. Space-division switching A. Shares a path using time slots B. Is always manual C. Provides a separate physical path per call D. Needs no control Answer: C. Time-division uses time slots. (Key point: Space vs time) 3. Switching by information transfer is A. Manual, automatic and electronic B. Space, time and frequency C. Strowger, crossbar and SPC D. Circuit, message and packet switching Answer: D. Transfer mode is separate from technology. (Key point: Transfer mode) 4. Which sequence is correct for digital switching functions? A. Receive digits, process/translate, busy test, interconnect, alert, supervise, release B. Release, ring, then receive digits C. Charge, then detect call D. Interconnect before receiving digits Answer: A. Call processing runs from attending to disconnection. 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