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.

• 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.

• 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.

• 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.

Terminating connectors
Single pair
Flat ribbon

• 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.

We can reduce the effect of cross talk & noise by using twisted wire.
Single pair
Insulating outer cover
Multicore

• 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.

In its simplest form, coaxial cable consists of a copper core, surrounded by plastic insulation and an outer braided copper.

It minimizes both effect: skin effect radiation effect

• 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 cladding
Single core
Plastic coating
Optical core
Multicore

• 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 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 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.

• 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-topoint 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 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 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 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).

• 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.