Communications Media Communications Medium / Media: Path over which, Messages can be sent for, Communication between the source and the receiver. 2 types: Guided Medium / Conducted Medium: It is visible. The device sends/conducts signals down the wire/cable. Example: Copper wire. Unguided Medium / Radiated Medium: It is invisible. Signal is sent/radiated through the air by means of a transmitter and an antenna. Example: Airwaves.
Communications Media Guided Media: Visible and are part of the physical portion of the network. 3 types of guided media: Twisted pair wire. Coaxial cable. Fiber-optic cable.
Twisted Pair Wire Cable Jacket Insulator (Plastic) Twisted Pair Cable Conductor 1 pair / 2 pairs / 4 pairs Single Communication Line RJ-11 Connector RJ-45 Connector Telephone Computer
Guided Media Twisted Pair Wire: Most common transmission medium in use. Construction / Composition: Has a core that consists of, 2 separate insulated copper wires, Twisted (intertwined) together a specific number of times per foot where, Each pair is considered a single communications line. Each wire in a twisted pair is coated with, An insulating material such as, Plastic. Bundles of twisted pair wires can be packed close together into one large cable. The insulation keeps the copper wires from touching, So the signal from one pair of wires does not interfere with the signal from any other pair of wires in the cable.
Guided Media Twisted Pair Wire: Need / Advantage of Twisting: When electricity flows through any wire, An electromagnetic field is generated. This energy can create interference on surrounding wires. When 2 wires are twisted together, The pair generates less energy than a single wire. So it makes the pair less susceptible to interference from neighboring wires. Therefore by reducing interference, Twisted pair wire provides a better quality media for transmission than wires without the twists.
Guided Media Twisted Pair Wire: 2 types: Unshielded Twisted Pair (UTP) Shielded Twisted Pair (STP)
Guided Media Twisted Pair Wire: Unshielded Twisted Pair (UTP): Does not have the extra wire wrapping of shielded twisted pair (STP) wire and therefore, Is more prone (susceptible) to interference. However it is sufficient (adequate) in areas with less chances of noise / interference. So often used in residential and office Telephone and Computer systems. Most homes, use 2 pairs (4 UTP wires) to connect their telephones to the local end office. 4 wires are used so that if a problem develops in 1 set of wires, the other set can be used until the problem is resolved. Less expensive than STP wires.
Guided Media Twisted Pair Wire: Shielded Twisted Pair (STP): Each pair of wires is placed into, A separate shield to absorb any interference. The wires are then put into a plastic outer shell. Reliable for transmitting data in, High-interference areas because the shielding prevents interference with the data. Example: Industry with large electronic equipments. More expensive than UTP wires.
Coaxial Cable Coaxial Cable Connector
Guided Media Coaxial Cable / Coax: Construction / Composition: Composed of a, Single copper wire (Inner conductor), Surrounded by an insulating material called, Shell Shell is surrounded by a second conductor called, Copper Mesh / Copper Shield. Gives the cable more electromagnetic protection than a twisted pair wire. The entire cable is enclosed in a plastic outer shell called the, Jacket. Characteristics: High-bandwidth medium that can carry thousands of signals at once. Can transmit data over long distances than Twisted Pair wire. Less susceptible/prone to interference than Twisted Pair wire.
Guided Media Coaxial Cable: Allows for 2 types of transmissions: Broadband Transmission Used by Cable Television Industry Baseband Transmission Used by Computers in a Local Area Network (LAN)
Broadband Transmission (Cable Television) Channel-1 Channel-2 Channel-3 Coaxial Cable Channel-5 Channel-4 ANALOG Transmission
(Computers) Baseband Transmission DIGITAL Transmission
Guided Media Coaxial Cable: Broadband Transmission: Used by cable television industry hence it is, Analog Transmission Single cable is logically divided by frequency into many channels, Each carrying a different transmission separated by, Guardbands to prevent, Interference between the signals. Using broadband transmission, a cable television company can, Transmit multiple channels to individual homes using only a single cable. Can also be used to transmit, Voice, Video, Data and Alarm Signals simultaneously in a Home security system.
Guided Media Coaxial Cable: Baseband Transmission: Only a single signal is transmitted over the cable. Computers use baseband transmission to, Send data to other computers in a local area network and hence it is, Digital Transmission
Guided Media Coaxial Cable: In spite of high bandwidth offered by coaxial cable, Twisted Pair (and not coaxial cable) is used more often in Computers and LAN’s because: Coaxial cable is more expensive than Twisted Pair Wire. Coaxial cable is difficult to install than Twisted Pair Wire. Coaxial cable is much larger and heavier than Twisted Pair Wire. Space required to store those cables is more.
Fiber-Optic Cable Fiber-Optic Cable Optical Fiber
Fiber-Optic Cable Principle Bouncing/Reflection off the walls Total Internal Reflection
Guided Media Fiber-Optic Cable: Uses light to transmit data signals. Construction / Composition: Fiber-Optic Cable is composed of, One or more thin strands of glass where, Each strand of glass is called: Optical Fiber Each ‘Optical Fiber’ is as thin as, A human hair and is surrounded by a layer called, Reflective buffer or Cladding. All the Optical Fibers are then enclosed in an outer covering called: Jacket
Guided Media Fiber-Optic Cable v/s Copper Wire: Fiber-Optic Cable: Signals are transmitted by means of light. Speed is much faster than copper wire. Copper Wire (Twisted Pair / Coaxial Cable): Transmit signals electrically. Speed is slower than fiber-optic cable.
Guided Media Fiber-Optic Cable: 2 types of fiber-optic cables based on, The method used to transmit light down the cable. Single-Mode Cable (Single Path / Single Signal): Multi-Mode Cable (Multiple Paths / Multiple Signals): Multimode Step Index Multimode Graded Index
Properties Fiber-Optic Cable Principle Transfer less data faster over long distances. Single-Mode Less Diameter Required: Transfer more data slower over short distances. MultiMode Step Index Signal might suffer: Loss of Strength (Attenuation) So needs to be regenerated after certain distance. MultiMode Graded Index More Diameter Required:
Guided Media Fiber-Optic Cable: Advantages: Offers high bandwidth. Can transmit huge amounts of data at very high speeds. Transmission speed starts from 100 Mbps and can go up to 2,500,000 Mbps. Much thinner and lighter than, Either twisted pair wire or coaxial cables. More secure. A copper wire is relatively easy to tap which, Allows someone to steal data without the owner ever knowing that the theft is occurring. With optical fiber, however, a tap is very difficult to perform. More immune (protection) to electrical interference. With copper wires, broken insulation can cause interference called: Crosstalk. Light waves do not interfere with each other even if the cables touch each other.
Guided Media Fiber-Optic Cable: Applications: Generally used to link together, LANs, WANs and other types of networks. Are not used to link an individual PC to a LAN because of, The high cost of the network interface cards and the other electronics needed.
Communications Media Unguided Media: Also called, Wireless Media / Radiated Media which do not use, Hard wires to transmit data. Example: Air is the best form of unguided media.
Unguided Media Transmitter Antenna Receiver Antenna Nature? Uni-directional / Omni-directional Directional / Un-directional
Communications Media Unguided Media: Question: Can any company start sending any signals (through air) for communication? Answer: No. Company needs to broadcast signals over specific frequency and, Allocation of frequency is regulated / controlled by, Some Government Regulatory Agency (such as TRAI) so that, Different forms of communications do not interfere with one another. Example: If a new radio station wants to begin broadcasting, It must get permission from Government Regulatory Agency to use the radio frequency over which it wants to broadcast.
Communications Media Unguided Media: Forms of transmission that use unguided media are: Broadcast Radio Microwave Cellular Radio Spread Spectrum Radio Infrared transmission
Unguided Media Frequency Spectrum
Unguided Media Frequency Spectrum
Unguided Media Broadcast Radio: Nature/Properties: Sends signals in a frequency range from, 540 KHz to 300 MHz Term usually is associated with: Radio Broadcasting through Radio Stations. Shortwave radio. CB radio. Television Transmission. Most forms of Broadcast Radio are, Omni-directional. ‘Omni’ means ‘All / Every’. Antenna that is used to receive the broadcast signal and, Does not have to be positioned or pointed in a specific direction.
Broadcast Radio Radio Broadcasting through Radio Stations: AM Radio: Stands for Amplitude Modulation Radio. Transmits at a much Lower Frequency than FM Radio and hence, Higher Wavelength than FM Radio and so, Can be broadcast farther than FM Radio. Interrupted easily by atmospheric changes such as thunderstorms. FM Radio: Stands for Frequency Modulation Radio. Transmits at a much Higher Frequency than AM Radio and hence, Lower Wavelength than AM Radio and so, Cannot be broadcast farther than AM Radio. Storm interference will not be noticeable.
Broadcast Radio Shortwave Radio: Used for communication in: Military communications. To give news during times of disaster. CB Radio: Stands for ‘Citizens Band Radio’. Uses very low power and cannot transmit over long distances. Was very popular in the 1970s and 1980s with travelers of all kinds. Truck drivers used CB radios to check on road conditions or get directions to their destinations.
Broadcast Radio Television Transmissions: Television transmission antenna sends a television signal out, In all the directions. Omni-directional. However, television receiving antenna (Yagi antenna) is, Directional and so, Pointing the television antenna more directly at the transmitting station will produce a better picture. Uses higher frequency than AM & FM radio because, More data consisting of both ‘Picture’ & ‘Sound’ need to be transferred. 2 basic types of television frequencies are used: VHF: Very High Frequency Frequencies from 50 to 225 MHz UHF: Ultra High Frequency Frequencies from about 400 to 900 MHz
Broadcast Radio Television Transmissions: DTV (Digital Television Technology): New technology that is used to transmit, Television channels in Digital form rather than Analog form. Decoder / Set-top box is used to decode the incoming signals. HDTV (High-Definition Television): Newer technology in DTV which, Delivers a higher-quality picture than standard television.
Unguided Media Microwave: Nature/Properties: Transmits signals between, 2 or more stations in a frequency range of: 3 GHz to 30 GHz (3,000 MHz to 30,000 MHz) Signals have a high frequency and hence, A short wavelength and so it is called, Micro. High frequency allows, Large amounts of data to be transmitted over this medium.
Unguided Media Microwave: Nature/Properties (cntd): Unlike ‘Broadcast Radio’ signals, which are omni-directional, Microwave transmission is, Uni-directional. Signals produced by a microwave station, Travel in a straight line and so, The antennas used for transmission must be pointed directly at one another. Also known as, ‘LINE OF SIGHT’ transmission. They can be affected by, Atmospheric changes such as rain and snow and by, Obstacles between the microwave stations.
Terrestrial Microwave Microwave To prevent obstacles, Earth Stations (Transmission/Receiving) are placed on a height. Satellite Microwave
Unguided Media Microwave: 2 types: Terrestrial Microwave Satellite Microwave
Microwave Terrestrial Microwave: Terrestrial means, Related to ground / territory / earth. So in terrestrial microwave, transmissions are sent between, 2 microwave stations on Earth. Because microwaves must travel in un-obstructed straight lines, Ground-based microwave stations are placed, On top of towers and, At very short distances from one another. If they were placed too far apart, Earth’s curvature blocked the line-of-sight transmission. Most common form of long-distance communications today as, Major long-distance telephone companies have microwave transmission towers placed across the nation where, Transmission could take place over 55 miles.
Microwave Satellite Microwave: Involves sending microwave transmissions between, 2 or more Earth-based microwave stations and, A satellite. Satellite just serves as a, Relay (Intermediate/Pass-on) station that receives signals from, One Earth-based station and rebroadcasts it to the next.
Objectives: Cover as much area as possible. Satellite Microwave Remain in the same place with respect to relative motion of earth. 22,300 miles 36,000 kms Footprint Geosynchronous Orbit GEOS Geosynchronous Earth Orbiting Satellite Geostationary Earth Orbiting Satellite
Microwave Satellite Microwave: Most communications satellites are placed into orbit at a distance which is, 22,300 miles above Earth’s surface known as, Geosynchronous Orbit / Geostationary Orbit At that distance, Satellite keeps revolving in orbit at the same rate as that of Earth’s rotation due to, Earth’s gravitational force and so, Satellite appears to be in a fixed position over the Earth. Such a satellite is called: GEOS Geo-synchronous Earth Orbiting Satellite Geo-stationary Earth Orbiting Satellite Part/Region of the earth that 1 satellite can cover is called: Footprint. Generally covers several countries. 3 satellites appropriately positioned over the Earth can cover entire Earth.
Conversion to a different frequency. Satellite Microwave Transponder long distance Amplification is done. Downlink Uplink 2 different frequencies Time wastage Propagation Delay
Microwave Satellite Microwave: Propagation Delay: Extra/Unnecessary time taken by the signal, To travel from an Earth station to a satellite and back plus, The time it takes to convert the signal to sending signal of different frequency. Varies from, 1 second for data transmission to, 3 seconds for voice or television transmission. Example: Television: When a reporter from one country interviews someone in another country. Telephone: Overseas telephone conversation also shows delay.
Microwave Satellite Microwave: Apart from GEOS satellites, other types of satellites also exist: LEOS. MEOS.