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Telecommunications System Components. Computer to process information. Terminals or input/output devices (source/destination) Communication channels => Communication channels use various communication media, such as telephone lines, fiber optic cables, coaxial cables, and wireless transmission.
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Telecommunications System Components • Computer to process information. • Terminals or input/output devices (source/destination) • Communication channels => Communication channels use various communication media, such as telephone lines, fiber optic cables, coaxial cables, and wireless transmission. • Communication processors => Modems, controllers, and front-end processors. • Communication software to control the function of the network.
Signal Attenuation • During the transmission through a medium, a signal is affected by attenuation, limited bandwidth, delay distortion, and noise. • When a signal propagates along a transmission medium its amplitude decreases. This is known as signal attenuation. • If the cable is longer, a number of repeaters (amplifiers) are inserted at some intervals so that the receiver can detect it.
Delay Distortion • A Digital signal consists of components with various frequencies. • The rate of propagation of a sinusoidal signal along a transmission line varies with the frequency of the signal. • Therefore, when we transmit any signal through a transmission line, all its components reach at the destination with varying delays. • This results in delay distortion.
Noise • In the absence of a signal, a transmission line ideally has zero electrical signal present. • In practice, however, there are random perturbations on the line even when no signal is being transmitted. • This is called line noise level.
Transmission medium: Two-wire open lines Terminating connectors Single pair Flat ribbon
Transmission medium: Two-wire open lines • Simplest transmission medium. • Each wire is insulated from the other and both are open to free space. • Up to 50 meters of direct connection with 19.2 kbps can be achieved. • It is mainly used to connect DTE (computer and DCE (modem). • Two types: single pair and multiple cable/flat ribbon cable. • Problems: • Crosstalk => cross-coupling of electrical signals between adjacent wires in the same cable. • Noise => The open structure makes it susceptible to pick up spurious noise signals from other electrical signal sources.
Communication Media: Twisted Wire We can reduce the effect of cross talk & noise by using twisted wire. Single pair Insulating outer cover Multicore
Communication Media: Twisted Wire • It consists of pairs of twisted copper wires. • It can be of two types: unshielded (UTP) and shielded (STP). • Telephone wire installation use UTP cabling. • UTP rated according to its quality: category 3 (Cat 3) and Cat 5 UTP. • Advantages: UTP is cheap, easy to install, and has a capacity from1 to 100 Mbps at distances up to 100meters • Disadvantages: slow, high-speed transmission causes interference (crosstalk), rapid attenuation, easy to eavesdrop. • STP is more expensive than UTP, and difficult to install. • STP has capacity of 500 Mbps at distances up to 100 meters.
Coaxial Cable In its simplest form, coaxial cable consists of a copper core, surrounded by plastic insulation and an outer braided copper.
Coaxial Cable It minimizes both effect: skin effect radiation effect
Coaxial Cable • Coax cable can be of two types depending on the thickness: thinnet coax and thicknet coax. • Thinnet coax is less costly than STP or Cat 5 UTP. • Thicknet coax is more expensive than STP or Cat 3 UTP. • Most commonly used for cable television installations. • A transmission medium consisting of thickly insulated copper wire, which can transmit a large volume of data than twisted wire. • Advantages: It is often used in place of twisted wire for important links in a network because it is a faster, more interference-free transmission medium. We can transmit 10 Mbps over several hundred meters.
Optical Fiber Optical core Optical cladding Plastic coating Single core Multicore
Optical Fiber • Optical fiber consists of a glass core, surrounded by a glass cladding with slightly lower refractive index. • In most networks fiber-optic cable is used as the high-speed backbone, and twisted wire and coaxial cable are used to connect the backbone to individual devices. • Advantages: faster, lighter, and suitable for transferring large amount of data. • Disadvantages: Fiber-optic cable is more difficult to work with, more expensive, and harder to install.
Optical Fiber • Optical fiber cable differs from both these transmission media in that it carries the transmitted information in the form of a fluctuating beam of light in a glass fiber. • Light transmission has much wider bandwidth. It can support bandwidths from 100 Mbps to greater than 2 Gbps and distances from 2 to 25 kilometers. • Optical transmission is immune to electromagnetic interference, crosstalk, and eavesdropping (more secure). • Optical fibers have low attenuation than copper, after every 30 miles we need to use a repeater, whereas in copper, we should insert repeaters at an interval of 2.8 miles .
Wireless Transmission • Wireless transmission sends signals through air or space without any physical wire. • Wireless media transmit and receive electromagnetic signals using methods such as infrared line of sight, high-frequency radio, and microwave systems. • Common uses of wireless data transmission include pagers, cellular telephones, microwave transmissions, communication satellites, mobile data networks, personal digital assistants, television remote controls.
Infrared Line of sight • It uses high-frequency light waves to transmit data on an unobstructed path between nodes (computers or some other devices such as printer) on a network, at a distance of up to 24.4 meters. • Use: The remote controls for most audio/visual equipment. TV, stereo, etc use infrared light. • Infrared equipment is relatively inexpensive. • Infrared systems can be configured as either point-to-point or broadcast. • Point-to-point systems require strict line-of-sight positioning. It supports up to 16 Mbps at 1 km. • With broadcast infrared communication, devices do not need to be positioned directly in front of each other, but have to be located within some distance. It supports less than 1 Mbps.
High-Frequency Radio • High-frequency radio signals can transmit data at rates of up to 11 Mbps to network nodes from 12.2 to 40 kilometers, depending on the nature of the obstructions between them. • Use: police vehicles use high-frequency radio signals for communication with each other. • Applications: • Pagers, cellular phones, and wireless networks Advantage: • The flexibility of the signal path makes high-frequency radio ideal for mobile transmissions. Disadvantages: • This medium is expensive due to • The cost of antenna towers • High-output transceivers. • Installation is complex and often dangerous due to high voltages • This medium is very susceptible to EMI and eavesdropping
Microwave • Microwave transmission is a high-frequency radio signal that is sent through the air using either terrestrial (earth-based) systems or satellite systems. • Both systems require line-of-sight communications between the sending signal and the receiving signal. • Terrestrial microwave uses antennas that require an unobstructed path or line-of-sight between nodes. • The cost of a terrestrial microwave system depends on the distance to be covered. • Businesses lease access to microwave system from service providers. • Data can be transmitted at 274 Mbps using terrestrial microwave. Attenuation is not a problem for shorter distance. • Signal can be obstructed over longer distances by weather conditions such as high winds and heavy rain for terrestrial microwave systems.
Terrestrial Microwave • Terrestrial microwave links are widely used to provide communication links when it is impractical or too expensive to install physical transmission media ( e.g. across a river, inaccessible terrain). • As the collimated microwave beam travels through the earth’s atmosphere, it can be affected by weather conditions. • However, with a satellite link the beam travels mainly through free space, therefore less prone to such effects (weather conditions).
Satellites • Satellite microwave uses a relay station that transfers signals between antennas located on earth and satellites orbiting the earth. • A satellite is a microwave station located in outer space. • Satellites used for communications are generally geostationary. • Geostationary satellite orbits the earth once in every 24 hours synchronously with the earth’s rotation .Therefore the satellites appear stationary from the ground. • Geosynchronous satellite rotate around the earth at 6900 miles/hour and remained positioned over the same point at 22300 miles above the equator. • Worldwide coverage can be achieved with three geosynchronous satellite spaced at 120 degrees interval from one another. • It can be used to access very remote and undeveloped locations on the earth. Data rate can be 90 Mbps. • Satellite systems are very expensive because it depend on space technology.. • Prone to attenuation, EMI, and eavesdropping.
