Telecommunications Fundamentals: Transmission Media, Wireless & Internet Protocols
Telecommunications Fundamentals
Broadcast Networks
Broadcast networks: receive user information and send it through terminals to access the network, without forming a point-to-point link (radio, TV, telephone).
Switched Networks
Switched networks: allow access to users through a node, dividing the network into parts, which is useful for local area extensions and the Internet.
Transmission Media
Electrical Conductors
Electrical conductors: used in telecommunications to transmit information in the form of electrical signals. They consist of metallic cables, of which there are two main types:
- Twisted pair cables: formed by twisted pairs of insulated wires. These cables are widely used in global telephone networks.
- Coaxial cable: formed by a central electrical conductor surrounded by a ground shield, which can carry thousands of telephone communications.
Fiber Optic
Fiber optic: transmits information using light through a cable instead of a metallic conductor. It has the same structure as a glass fiber core with a diameter similar to a hair.
To transmit large amounts of data, multifiber cables are used, which are protected by a plastic sponge and a metallic reinforcement (Kevlar).
Electromagnetic Waves
Electromagnetic waves: consist of perpendicular electric and magnetic fields that spread at the speed of light.
Advantages of electromagnetic waves:
- No need for a physical medium for propagation
- Long-distance propagation and speed
- Able to pass through opaque obstacles
Disadvantages: they attenuate with distance, although it is possible to minimize this with amplified waves.
Telecommunications Using Electromagnetic Waves
In telecommunications, two types of electromagnetic waves are mainly used: radio waves and microwaves.
Radio Waves
Radio waves are electromagnetic signals that spread through space. Wavelength is inversely proportional to frequency (number of cycles per second).
- AM (Amplitude Modulation): long distance, large amplitude; it reaches far but is prone to interference.
- FM (Frequency Modulation): the frequency of the carrier wave varies with the modulating signal, offering better quality.
- Phase Modulation: used for digital transmissions. The carrier signal's phase depends on the modulating signal.
Short-Range Wireless Technologies
Bluetooth: a wireless communication system using radio waves that allows fast and reliable connections (10–100 m).
Features: service integration, omnidirectional transmission, security, and network establishment.
Wi-Fi (Wireless Fidelity): a radio-frequency communication protocol that allows wireless communication without cables, connecting devices through a router.
Infrared: a wireless communication system based on infrared light, operating over short distances of about 1 m with a viewing angle of 30°.
Microwaves
Microwaves are electromagnetic waves that fall between infrared and conventional radio waves. They transmit in a directional manner, and parabolic antennas are used to concentrate the radiated energy.
Satellite Communication
- Geostationary satellites: orbit in a circular equatorial path.
- Medium-orbit satellites: cover the whole Earth.
- Low-orbit satellites: about 40 satellites are needed to cover any point on the ground.
Mobile Communication
UMTS (Universal Mobile Telecommunications System) is a 3G radio communication system developed to allow mobile access to the Internet service.
Global Navigation Satellite Systems (GNSS)
- GPS (Global Positioning System): uses the Navstar constellation of 24 satellites and a network of ground stations distributed across five stations. GPS receivers receive signals from the satellites and calculate the user's position.
- GLONASS (Global Navigation Satellite System): uses 24 satellites and a time reference system different from GPS.
- Galileo: a global navigation system made up of 30 satellites. Advantages: greater precision than GPS, wider range and better signal availability, and independence from GPS.
Protocols and Internet Connections
Protocol: a set of rules on how to perform tasks.
TCP/IP allows computers and networks to communicate.
- TCP: Transmission Control Protocol.
- IP: Internet Protocol.
Dial-Up Modem
The modem works with analog signals when connected to the telephone line. It must be used as a modulator-demodulator. Advantages: low cost connection. Disadvantage: slow speed.
Broadband
Broadband: the maximum amount of data that can pass through a communication path, measured in Kbps or Mbps.
- ADSL (Asymmetric Digital Subscriber Line): a high-speed line with three channels: two for high-speed data and one for normal voice communication.
- Cable: uses a hybrid fiber-coaxial (HFC) network and delivers the service through the same cable.