--- title: "Exchange types and essential features" subject: "Telecommunications" chapter: 1 key: "semester_8/telecommunications:exchange-types-essential-features" source: https://www.bctengineer.com/q/semester_8/telecommunications/exchange-types-essential-features site: BCT Engineering --- # Exchange types and essential features Telecommunications · Chapter 1: Telecommunication Networks - Asked in: 2080 Chaitra, 3+5 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/telecommunications/exchange-types-essential-features - Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-1 ## Question What do you mean by an exchange telecommunication and its type. Describe essential features of an exchange showing major equipment. ## Short answer An exchange is a switching node connecting subscriber lines and trunks on demand. Types: manual, electromechanical (Strowger, crossbar), electronic SPC (space/time-division), softswitch, and by function local, tandem, trunk, gateway, PBX. Essential equipment includes MDF, subscriber line interface (BORSCHT), switching network, control processor, signalling units, trunk interfaces, billing, O&M, power plant, and synchronisation clock. ## Answer #### Exchange and its types A **telecommunication exchange** (switching centre) is a node of the network where subscriber lines and trunks terminate and where connections are set up between them on demand, supervised during the call and released at the end. **Types** - By technology: - **Manual exchange** – operator connects calls with cords on a switchboard (local battery or central battery). - **Automatic electromechanical** – Strowger (step-by-step) and crossbar exchanges. - **Electronic SPC exchange** – computer-controlled; space-division (analogue) or time-division (**digital**) switching. - **Softswitch / IP exchange** – call control in software, media carried as packets. - By function/position in network: - **Local (end) exchange**, **tandem exchange** (joins local exchanges in a city), **trunk/toll (transit) exchange**, **international gateway exchange**, and private exchanges (**PBX/PABX**) for organisations. #### Essential features and major equipment ```text Subscriber lines │ MDF ─> Subscriber ─> Switching ─> Trunk ─> other line units network units exchanges │ │ │ └──── Control (processor) ┘ + signalling units O&M terminal, billing, power plant ``` 1. **Main Distribution Frame (MDF):** terminates outside cables; cross-connects lines to equipment; protection against lightning/over-voltage. 2. **Subscriber line interface (BORSCHT):** Battery feed, Over-voltage protection, Ringing, Supervision (on/off-hook), Codec, Hybrid (2W/4W), Testing. 3. **Switching network (fabric):** space or time switches that connect inlets to outlets. 4. **Control subsystem:** processor(s) with stored program that do call processing, routing and number translation. 5. **Signalling equipment:** dial pulse/DTMF receivers, tone generators (dial, busy, ringback), inter-exchange signalling (CAS, SS7). 6. **Trunk interfaces:** connect PCM/E1 trunks to other exchanges. 7. **Charging/billing** equipment and call records. 8. **Operation and maintenance (O&M):** terminals, alarms, test equipment. 9. **Power plant:** −48 V DC battery with rectifiers and generator for uninterrupted service. 10. **Synchronisation (clock)** in digital exchanges. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which classification is by technology? A. Local, tandem, trunk and international gateway B. Manual, automatic electromechanical, electronic SPC and softswitch/IP C. PBX, PABX and MDF D. Space, quaternary and tertiary Answer: B. Local/tandem/trunk is by function and position; the first list is by technology. (Key point: Types) 2. What does the Main Distribution Frame do? A. Stores the call-processing program B. Generates ringback tone C. Terminates outside cables, cross-connects lines to equipment and gives over-voltage protection D. Charges the −48 V battery Answer: C. The MDF is the entry point of subscriber cables, with protection. (Key point: MDF) 3. In BORSCHT, what does the 'R' stand for? A. Registers B. Routing C. Rectification D. Ringing Answer: D. BORSCHT: Battery feed, Over-voltage protection, Ringing, Supervision, Codec, Hybrid, Testing. (Key point: BORSCHT) 4. What is the role of the control subsystem? A. Processor(s) with stored program do call processing, routing and number translation B. It terminates trunks physically C. It supplies DC power D. It cross-connects cables at the frame Answer: A. The control subsystem is the brain of the exchange. (Key point: Control) 5. Which power arrangement is used for uninterrupted service? A. 230 V AC mains only B. −48 V DC battery with rectifiers and generator C. 12 V solar panel only D. Unregulated AC from a transformer Answer: B. A battery plant with rectifiers and a generator keeps the exchange running. 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