Telecommunications Fundamentals

Evolution of Telecommunications

Telecommunication is the transmission and reception of information over distance using electrical, optical, or radio signals. It carries speech, text, data, images, and video.

• Automation: Automatic exchanges replaced operators who manually connected calls; stored-program control later made call handling and supplementary services software-controlled.

• Digitisation: PCM coding, regenerative transmission, and digital switching replaced many analog transmission and switching systems.

• Packet convergence: Voice, video, and data increasingly share IP transport instead of requiring separate service-specific networks.

Evolution of telecommunications.

Date / era	Milestone and significant technology	Importance, including multiplexing
1837-1844	Electrical telegraph and Morse code	Coded pulses provided rapid long-distance text communication.
1874	Baudot multiplex telegraph	Synchronous time sharing let several telegraph streams use one line, an early form of TDM.
1876-1878	Telephone and the first commercial manual exchange	Electrical speech enabled real-time conversation; operators established dedicated circuits.
1891-1892	Strowger automatic exchange	Subscriber dialling introduced automatic electromechanical circuit switching.
1895-1901	Wireless telegraphy	Radio removed the physical-wire requirement and enabled maritime and long-distance wireless links.
1910s-1930s	Electronic repeaters, carrier telephony and coaxial cable	Amplified long-haul trunks increased range; FDM carried many analog calls in separate frequency bands.
1937-1948	PCM principle, transistor and information theory	Established the basis for sampled speech, electronic equipment, channel capacity and error-control coding.
1950s-1962	Terrestrial microwave, communication satellites and T1 PCM	Microwave and Telstar extended long-distance reach; commercial PCM trunks used regenerative transmission and TDM.
1965-1970s	Stored-program control and digital exchanges	Software replaced hard-wired call control; time-slot interchange switched PCM channels efficiently.
1966-1977	Optical-fibre proposal, low-loss fibre and field deployment	Fibre provided low-loss, high-bandwidth trunks and later became the backbone medium.
1969; 1983	ARPANET packet switching; TCP/IP adoption	Statistical multiplexing shared links among bursty data flows and interconnected unlike networks.
1979-1991	Commercial 1G cellular followed by GSM 2G	Cellular frequency reuse enabled mobility; 2G added digital voice, encryption, SMS and FDMA/TDMA access.
1988-1990s	SONET/SDH and WDM/DWDM	Synchronous optical hierarchies simplified transport; WDM carried many wavelengths on one fibre.
1990s-2000s	Internet, VoIP, DSL/cable/FTTH and IP/MPLS	Voice, video and data converged on broadband packet networks with statistical sharing and QoS.
2001; 2009; 2019	Commercial 3G, 4G LTE and 5G NR	Mobile service evolved from WCDMA packet data to all-IP OFDMA, MIMO, low latency and massive connectivity.

Note

Three parallel evolution paths:

switching progressed from manual to automatic, SPC, digital and software-controlled systems; transmission progressed from copper to coax/microwave, satellite, fibre and broadband radio; multiplexing progressed from space sharing to FDM, TDM, statistical packet multiplexing, WDM and OFDM/OFDMA.

[!NOTE]

Coexisting technologies

• Optical links can carry circuit-switched or packet-switched traffic; radio links can carry analog or digital signals.

• Old and new networks coexist during migration. Gateways translate signalling and media formats where their interfaces differ.

Analog and Digital Telecommunications

Basis	Analog telecommunications	Digital telecommunications
Information representation	A continuously varying signal parameter represents the message	Discrete symbols represent coded information
Repeater action	Amplification increases signal and accumulated noise	Regeneration decides symbols and reconstructs the waveform
Noise performance	Noise and distortion accumulate along cascaded links	Decisions tolerate limited noise; excessive impairment produces bit errors
Multiplexing	FDM is common in legacy analog trunks	TDM and packet multiplexing are common; digital systems can also use frequency channels
Processing	Analog filtering, amplification and modulation	Digital coding, switching, compression and encryption
Limitations	Difficult noise removal and less flexible processing	Quantisation, clock recovery, coding overhead and processing delay
Examples	Analog telephone loops, AM/FM broadcasting	PCM trunks, Ethernet, digital cellular and IP voice

Note

Data type vs signal type

• Analog data varies continuously; digital data consists of discrete values. Either can be represented by electrical, optical, or radio signals.

• A digital radio transmitter maps bits to a finite set of carrier states, but the transmitted electromagnetic waveform remains a physical, continuous-time signal.

Convergence of Voice, Data and Video

Convergence carries services such as VoIP, video calls, IPTV, messaging, and web access over a common access, aggregation, and core infrastructure.

1. Source coding: Voice is sampled and coded; video is encoded, usually with compression. Protocols package these streams and computer data into packets.

2. Shared transport: Switches and routers forward packets over the same links using destination addresses or labels. Capacity is shared between active services.

3. Session control: Control systems authenticate users, establish sessions, and apply service policy. Gateways interwork with legacy signalling and media formats.

4. QoS: Classification and scheduling give delay-sensitive traffic suitable treatment; admission control can reject sessions when adequate resources are unavailable.

• Advantages: Shared links improve utilisation, and a common management platform reduces the need to operate separate networks for each service. Applications can combine voice, video, and data in one session.

• Constraints: IP alone guarantees neither low delay nor availability. A shared-network failure can interrupt several services at once, so capacity planning, security, path redundancy, and power backup are essential.

Telecommunication Network

A telecommunication network is an interconnected system of terminals, transmission links, switching nodes and control systems that transfers information between users or devices.

Architecture of a telecommunication network.

Components and Functions

Component	Function	Examples
End system	Generates or consumes information and interfaces it to the network	Telephone, computer, mobile handset, sensor
Access network	Connects the subscriber to the first provider node	Copper local loop, FTTH, cellular radio access
Aggregation network	Combines traffic from many access nodes and transports it toward the core	Metro Ethernet, optical aggregation ring
Core or backbone	Carries large traffic volumes between regions, gateways and service networks	IP/MPLS core, optical backbone
Switching system	Selects outgoing resources and transfers information toward the destination	Telephone exchange, Ethernet switch, router
Transmission system	Carries signals between nodes using a physical medium	Fibre link, microwave hop, copper cable
Signalling system	Establishes, supervises, modifies and releases connections or sessions	SS7, SIP, subscriber signalling
Network management	Monitors and configures equipment, measures performance and manages faults	OSS, network management system

One node may perform several functions: a telephone exchange can terminate transmission links, switch bearer channels, and process call signalling.

Access, Aggregation and Core Hierarchy

• Access: Copper loops, FTTH, cellular radio, or Wi-Fi connect subscribers to the first provider node. Coverage and cost per subscriber strongly influence the design.

• Aggregation: Combines traffic from access nodes onto higher-capacity regional links, applies service policies, and provides protected paths toward the core.

• Core: Carries high aggregate traffic between regions and service networks. Fast forwarding, alternate routes, and high availability are required because many users depend on each core link.

• Interconnection: Border routers and gateways exchange traffic with other operators, the Internet, and international networks, applying routing and interworking policies.

A local call may remain within one exchange or region; a long-distance call crosses additional switching and transmission nodes. The route need not traverse every hierarchy level.

Network Planes

Plane	Information carried	Typical functions
User or bearer plane	Voice samples, application data and video packets	Media transport and forwarding
Control plane	Connection, routing and session-control information	Call setup/release, route exchange and resource control
Management plane	Configuration, alarms, measurements and administrative information	Fault, configuration, accounting, performance and security management

Note

Logical separation of planes

• User, control, and management traffic can share physical links while using distinct channels, protocols, VLANs, labels, or forwarding policies.

• A bearer path carries the conversation or application data; its control messages establish or modify how that traffic is handled.

Circuit-Switched and Packet-Switched Networks

• Circuit switching: Reserves channel capacity along a path before transfer and holds it until release, including periods when the source is silent.

• Packet switching: Divides information into packets whose headers guide forwarding. Active users share link capacity statistically; packets may queue when their combined arrival rate exceeds the outgoing capacity.

Basis	Circuit-switched network	Packet-switched network
Setup	Normally required before user information transfer	Not required for IP datagrams; some packet services establish logical connections
Capacity	Reserved for the connection	Shared statistically unless additional reservation mechanisms are used
Transfer unit	Continuous stream within the allocated channel	Packet or frame
Delay	Predictable after setup, subject to transmission and processing	Variable with queueing, route and network load
Bursty traffic	Reserved capacity may remain unused	Capacity can be used by other active sources
Impairment under load	New calls may be blocked	Packets may be delayed or discarded
Applications	Traditional telephone circuits, leased channels	Internet data, modern voice/video and converged networks

Transmission Media

The transmission medium carries signal energy from transmitter to receiver.

• Guided media: Conductors or dielectric waveguides constrain propagation, as in twisted pair, coaxial cable, and optical fibre.

• Unguided media: Antennas transmit and receive electromagnetic waves through free space, as in terrestrial radio, microwave, and satellite links.

Guided Media

Cross-sections of guided transmission media.

Twisted pair:

• Construction: Two insulated conductors twisted together.

• Performance: Balanced signalling and the changing orientation of the pair reduce pickup of external interference and coupling to neighbouring pairs.

• Limitations: Twisting reduces, but does not eliminate, crosstalk. Attenuation and usable bandwidth depend on cable category, conductor size, frequency and length.

• Applications: Telephone local loops, DSL and Ethernet.

Coaxial cable:

• Construction: An inner conductor, dielectric and concentric outer conductor.

• Performance: The outer conductor provides shielding and a return path, while the geometry determines the characteristic impedance. Coax offers controlled RF performance and good interference rejection.

• Limitations: Loss increases with frequency, and the cable is bulkier than an individual twisted pair.

• Applications: Antenna feeders, cable television and RF interconnections.

Optical fibre:

• Construction: A light-guiding core surrounded by cladding. In the usual step-index description, the core has a higher refractive index than the cladding.

• Performance: Low attenuation, high capacity, electrical isolation and immunity to electromagnetic interference.

• Limitations: Dispersion, bending, connector/splice loss and optical receiver sensitivity limit link performance.

• Applications: FTTH, metropolitan networks, backbones and submarine systems.

Unguided Media

Radio, microwave and satellite links.

Radio links:

• Operation: Use transmitting and receiving antennas.

• Propagation: Depending on frequency and environment, propagation can involve line of sight, diffraction, reflection, scattering, ground waves or ionospheric effects.

• Capabilities: Enable broadcasting and mobility.

• Limitations: Exposed to interference, fading and spectrum constraints.

Terrestrial microwave links:

• Configuration: Commonly use high-gain directional antennas between fixed sites.

• Link requirements: Adequate line of sight and Fresnel-zone clearance are needed.

• Performance: Directionality permits spatial reuse.

• Limitations: Terrain, Earth curvature, fading and, at higher frequencies, rain attenuation constrain the link.

• Applications: Point-to-point backhaul and links across difficult terrain.

Satellite links:

• Operation: Relay signals between Earth stations through an orbiting transponder or regenerative payload. The uplink reaches the satellite, and the downlink reaches the destination.

• Coverage: Provide broad coverage and connectivity where terrestrial infrastructure is difficult.

• Limitations: Path loss, antenna requirements, weather effects in some bands and propagation delay are major constraints.

• Orbit effects: GEO links have much longer propagation delay than typical terrestrial links; lower orbits reduce path delay but require moving coverage and handover management.

Classification: Microwave and satellite systems both use radio-frequency electromagnetic waves. They are listed separately because their network geometry, equipment and applications differ.

Media Comparison

Medium	Capacity and interference	Reach and deployment	Typical use
Twisted pair	Rate depends on category and length; balance and twisting reduce interference	Low cable cost; high rates usually require short runs	Telephone access, DSL, LANs
Coaxial cable	Wide RF bandwidth and good shielding; loss increases with frequency	Moderate cable and connector cost; amplifiers can extend reach	Antenna feeders, CATV, RF equipment
Optical fibre	High capacity, low attenuation, immunity to electromagnetic interference	Long reach; dispersion, civil works, and termination affect design and cost	FTTH, metro, backbone, submarine links
Radio access	Spectrum is shared; interference and fading limit capacity	Supports mobility without individual cables to users	Cellular access, broadcasting, WLAN
Terrestrial microwave	Directional point-to-point links; link margin accommodates fading	Needs path clearance and suitable sites; tower costs can dominate	Backhaul and regional links
Satellite	Shared spectrum, high path loss, band-dependent weather effects	Wide coverage; orbit, terminal cost, and latency determine suitability	Remote access, broadcasting, backup links

Selection Criteria

• Rate and reach: Verify the required data rate over the full link distance, allowing for attenuation, dispersion, interference, receiver sensitivity, and the target BER.

• Site and service: Check terrain, cable access or radio-path clearance, mobility, maintenance access, security, and required availability. Redundant links may be needed where one failure would interrupt essential service.

• Cost and regulation: Compare installation and operating costs, including civil works, towers, equipment, and maintenance. Wireless systems also require suitable spectrum and compliance with licensing and power limits.