Evolution of telecommunication and switching systems

Telecommunication

Telecommunication is communication at a distance: the transmission, emission or reception of signs, signals, writing, images, sounds or data of any kind by wire, radio, optical or other electromagnetic systems (ITU definition). A telecom system has terminals, transmission links and switching (exchanges) that connect any user to any other user on demand.

Evolution of telecommunication with switching

The growth of telecom is closely tied to the way calls were switched:

1. Telegraph era (1837–1876) – Morse's electric telegraph (1837/1844). Messages were carried by hand or by store-and-forward at telegraph offices (message switching by operators).
2. Telephone and manual switching (1876–1890s) – Bell's telephone (1876). With many telephones, point-to-point wiring needs $n(n-1)/2$ lines, so the manual exchange (first at New Haven, 1878) was introduced. Operators connected calls with cords and jacks on a switchboard; early boards used local-battery and later central-battery (CB) systems.
3. Automatic electromechanical switching
   • Strowger step-by-step (1889–1892) – Almon B. Strowger invented a two-motion selector driven directly by dial pulses; the first automatic exchange opened at La Porte, USA (1892). The rotary dial followed in 1896.
   • Crossbar switching (1920s–1950s) – crossbar switch with common control (markers, registers); faster, less wear, more flexible routing.
4. Electronic switching – Stored Program Control (SPC), 1965 – Bell's No. 1 ESS: switching controlled by a computer program. Easy to add services (abbreviated dialling, call forwarding), centralised and later distributed control. The switching fabric was still space-division (reed relays).
5. Digital time-division switching (1970s) – with PCM, speech is digitised and switched using time slots (TSI, T-S-T networks): E10 (France, 1970), No. 4 ESS (1976), and later EWSD, 5ESS, AXE. Smaller, cheaper, works with digital transmission (integrated digital network) and common channel signalling (SS7).
6. ISDN and packet switching (1980s) – end-to-end digital voice and data; X.25 and later frame relay, ATM.
7. Mobile and IP era (1990s–now) – mobile switching centres (GSM), softswitches, IMS and all-IP networks (VoIP, 4G/5G core), where calls are carried as packets and switching is done by routers and software.

Each step reduced manual work, increased speed and capacity, and added new services.