PERFORMANCE STANDARD Given a network system, identify and illustrate the different data communications components clearly Objectives: Define elements of a communication system Define data communications Discuss various types of transmission media and their characteristics Discuss encoding of information tor transmission Discuss types of signal & their characteristics Relate data capacity of a channel and bandwidth Classify media based on bandwidth Discuss channel organization
Discuss various types of transmission media and their characteristics
twisted pair – telephone cable coaxial cable –Thick black cable used for higher bandwidth communications than twisted pair (i.e. Optus cable) fibre optic – data transferred through pulses of light. Extremely fast. Non cable methods such as satellite, microwave, wireless and Bluetooth
Twisted pair cable application Most common medium Telephone network Between house and local exchange (subscriber loop) Within buildings To private branch exchange (PBX) For local area networks (LAN) 10Mbps or 100Mbps
Twisted pair cable pro and contra Advantages Cheap Easy to work with Disadvantages Low data rate Short range
Twisted pair Transmission Characteristics Analog Amplifiers every 5km to 6km Digital Use either analog or digital signals repeater every 2km or 3km Limited distance Limited bandwidth (1MHz) Limited data rate (100MHz) Susceptible to interference and noise
Twisted pair (UTP and STP) Unshielded Twisted Pair (UTP) Ordinary telephone wire Cheapest Easiest to install Suffers from external EM interference Shielded Twisted Pair (STP) Metal braid or sheathing that reduces interference More expensive Harder to handle (thick, heavy)
The Electronic Industries Association (EIA) has developed standards to grade UTP. 1. Category 1. The basic twisted-pair cabling used in telephone systems. This level of quality is fine for voice but inadequate for data transmission. 2. Category 2. This category is suitable for voice and data transmission of up to 2Mbps. 3. Category 3.This category is suitable for data transmission of up to 10 Mbps. It is now the standard cable for most telephone systems. 4. Category 4. This category is suitable for data transmission of up to 20 Mbps. 5. Category 5. This category is suitable for data transmission of up to 100 Mbps.
The most common UTP connector is RJ45 (RJ stands for Registered Jack).
Coaxial Cable (or coax) Coaxial cable carries signals of higher frequency ranges than twisted-pair cable. Coaxial Cable standards: RG-8, RG-9, RG-11 are used in thick Ethernet RG-58 Used in thin Ethernet RG-59 Used for TV
Coaxial Cable Used for cable television, LANs, telephony Has an inner conductor surrounded by a braided mesh Both conductors share a common center axial, hence the term co-axial
Coax Layers copper or aluminum conductor insulating material shield (braided wire) outer jacket (polyethylene)
Coaxial Cable Applications: Most versatile medium Television distribution Ariel to TV Cable TV Long distance telephone transmission Can carry 10,000 voice calls simultaneously Being replaced by fiber optic Short distance computer systems links Local area networks
Coaxial Cable - Transmission Characteristics Analog Amplifiers every few km Closer if higher frequency Up to 500MHz Digital Repeater every 1km Closer for higher data rates
Fiber Optic Cable Relatively new transmission medium used by telephone companies in place of long- distance trunk lines Also used by private companies in implementing local data communications networks Require a light source with injection laser diode (ILD) or light-emitting diodes (LED)
consists of three concentric sections plastic jacketglass or plastic cladding fiber core
Fiber Optic Cable Metal cables transmit signals in the form of electric current. Optical fiber is made of glass or plastic and transmits signals in the form of light. Light, a form of electromagnetic energy, travels at 300,000 Kilometers/second (186,000 miles/second), in a vacuum. The speed of the light depends on the density of the medium through which it is traveling (the higher density, the slower the speed).
multimode step-index fiber the reflective walls of the fiber move the light pulses to the receiver multimode graded-index fiber acts to refract the light toward the center of the fiber by variations in the density single mode fiber the light is guided down the center of an extremely narrow core
greater capacity (bandwidth of up to 2 Gbps) smaller size and lighter weight lower attenuation immunity to environmental interference highly secure due to tap difficulty and lack of signal radiation
expensive over short distance requires highly skilled installers adding additional nodes is difficult
Unguided media, or wireless communication, transport electromagnetic waves without using a physical conductor. Instead the signals are broadcast though air or water, and thus are available to anyone who has a device capable of receiving them. The section of the electromagnetic spectrum defined as radio communication is divided into eight ranges, called bands.
Electrical conductor (or system of..) used to radiate electromagnetic energy or collect electromagnetic energy Transmission Radio frequency energy from transmitter Converted to electromagnetic energy By antenna Radiated into surrounding environment Reception Electromagnetic energy impinging on antenna Converted to radio frequency electrical energy Fed to receiver Same antenna often used for both
transmission and reception are achieved by means of an antenna directional transmitting antenna puts out focused beam transmitter and receiver must be aligned omnidirectional signal spreads out in all directions can be received by many antennas
Directional Antennas provide great efficiency of power transmission because the power can be focused into a narrow beam directed toward the station of interest.
Omnidirectional Antenna is widely used for radio broadcasting antennas, in mobile devices that use radio such as cell phones, FM radios, walkie-talkies, wireless computer networks, cordless phones, GPS
Radio technology considers the earth as surrounded by two layers of atmosphere: the troposphere and the ionosphere. The troposphere is the portion of the atmosphere extending outward approximately 30 miles from the earth's surface. The troposphere contains what we generally think of as air. Clouds, wind, temperature variations, and weather in general occur in the troposphere. The ionosphere is the layer of the atmosphere above the troposphere but below space.
Ground propagation: radio waves travel through the lowest portion of the atmosphere, hugging the earth. These low-frequency signals emanate in all directions from the transmitting antenna and follow the curvature of the planet. The distance depends on the power in the signal. In Sky propagation, higher-frequency radio waves radiate upward into the ionosphere where they are reflected back to earth. This type of transmission allows for greater distances with lower power output. In Line-of-Sight Propagation, very high frequency signals are transmitted in straight lines directly from antenna to antenna.
BandRangePropagationApplicationVLF3–30 KHzGroundLong-range radio navigation LF30–300 KHzGround Radio beacons and navigational locators MF300 KHz–3 MHzSkyAM radio HF3–30 MHzSky Citizens band (CB), ship/aircraft communication VHF30–300 MHz Sky and line-of-sight VHF TV, FM radio UHF300 MHz–3 GHzLine-of-sight UHF TV, cellular phones, paging, satellite SHF3–30 GHzLine-of-sightSatellite communication EHF30–300 GHzLine-of-sightLong-range radio navigation
Satellite is relay station Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency Requires geo-stationary orbit Height of 35,784km Television Long distance telephone Private business networks