Telecommunications System Components Computer to process information. Terminals or input/output devices (source/destination) Communication channels =>

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.

Effect of imperfect transmission medium

Sources of attenuation and distortion

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

Single pairFlat ribbon

Terminating connectors

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

Insulating outer cover

Single pair

Multicore

We can reduce the effect of cross talk & noise by using twisted wire.

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 CableIt 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

Plastic coating

Single core

Opticalcore

Opticalcladding

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 networksAdvantage:• 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.