--- title: "Major types of telephone exchanges" subject: "Telecommunications" chapter: 1 key: "semester_8/telecommunications:telephone-exchange-major-types" source: https://www.bctengineer.com/q/semester_8/telecommunications/telephone-exchange-major-types site: BCT Engineering --- # Major types of telephone exchanges Telecommunications · Chapter 1: Telecommunication Networks - Asked in: 2070 Asar, 3+4 marks - Video: [What is exchange in telecommunication?](https://www.youtube.com/watch?v=YmHURFgS95g) — TEACH TREE - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/telecommunications/telephone-exchange-major-types - Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-1 ## Question What is telephone exchange? Describe the major types of telephone exchanges in brief. ## Short answer A telephone exchange is a switching centre that connects, supervises and releases temporary paths between subscribers. Major types: manual (magneto or central battery), Strowger, crossbar, electronic SPC (space or time division), and by role local, tandem, toll, international gateway and PBX. ## Answer #### Telephone exchange A **telephone exchange** is the switching centre where subscriber lines and trunks end, and where a temporary path is set up between a calling and a called subscriber on demand, supervised and then released. It removes the need for direct lines between every pair of users. #### Major types 1. **Manual exchange** – an operator connects calls with cords and jacks. - *Local battery (magneto):* each telephone has its own battery; caller turns a magneto to signal. - *Central battery (CB):* battery at the exchange; lifting the handset lights a lamp at the switchboard. 2. **Strowger (step-by-step) exchange** – electromechanical; two-motion selectors step directly with dial pulses (direct control). 3. **Crossbar exchange** – electromechanical crossbar switches with **common control** (registers, markers); faster and more reliable than Strowger. 4. **Electronic (SPC) exchange** – a stored-program computer controls the switching network; offers many services. - *Space-division* – separate metallic/reed-relay path for each call. - *Time-division (digital)* – PCM speech switched in time slots (e.g. E10, EWSD, 5ESS, AXE); used in modern networks. 5. **Exchanges by network role:** local (end) exchange, tandem exchange, toll/trunk exchange, international gateway, and private branch exchange (PBX/PABX) in offices. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why is a telephone exchange used? A. To amplify speech on long lines B. To set up a temporary path between any caller and called subscriber on demand, avoiding direct lines between every pair C. To generate ringing only D. To store telephone numbers permanently Answer: B. An exchange switches a temporary path on demand, so permanent direct links between all pairs of users are not needed. (Key point: Purpose of an exchange) 2. What distinguishes a crossbar exchange from a Strowger exchange? A. Crossbar uses direct control by dial pulses B. Crossbar uses common control (registers, markers) and is faster and more reliable C. Crossbar has no switches D. Crossbar is a stored-program digital exchange Answer: B. Strowger is direct-control step-by-step; crossbar uses common control with registers and markers. (Key point: Strowger vs crossbar control) 3. In a time-division (digital) SPC exchange, how is speech switched? A. As analogue signals on a separate metallic path per call B. As PCM speech in time slots under stored-program control C. By an operator with cords D. By two-motion selectors Answer: B. Digital SPC exchanges (E10, EWSD, 5ESS, AXE) switch PCM speech in time slots; space-division uses a separate path per call. (Key point: Electronic SPC exchanges) ## Related in Telecommunications - [Drawbacks of manual telephone exchanges](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Amanual-exchange-drawbacks) — Telecommunications, chapter 1 - [Working principle of a digital telephone exchange](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Adigital-telephone-exchange-principle) — Telecommunications, chapter 4, asked 4× - [Telephone exchange and switching hierarchy](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aexchange-switching-hierarchy) — Telecommunications, chapter 1, asked 3× - [Telephone exchange structure; TST vs STS](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aexchange-structure-tst-sts) — Telecommunications, chapter 4 - [Short note: Telephone numbering in PSTN](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Ashort-note-pstn-numbering) — Telecommunications, chapter 7, asked 2× - [Digital exchange and three-stage crosspoints](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Adigital-exchange-crosspoints) — Telecommunications, chapter 4 ## Related in other subjects - [Succession of events; GPSS telephone model](https://www.bctengineer.com/question.md?key=semester_8%2Fsimulation_and_modeling%3Agpss-telephone-system) — Simulation and Modeling, chapter 9 - [8086 speed over 8-bit; major registers](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3A8086-faster-registers) — Microprocessor, chapter 3 - [Three major IC technologies](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Athree-major-ic-technologies) — Embedded System, chapter 8 - [Major components of a power station and functions](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Apower-station-components-functions) — Power System Analysis I, chapter 1