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Introduction Outline to n Terminology Data Communication n Transmission medium n Guided media Unguided media DCS201- Computer Science n By: Dilum BandaraData Communication Terminologyn Is the process of transmitting data from n Bit rate one computer to another n Number of bits per second Given in bps Focus is on the transmission medium, nn n Baud rate different signal levels & data coding n Number of signal variations per second n Given in bauds per sec n Bandwidth n Maximum frequency supported by the mediumTransmission Medium Guided median Provides the path for data n Copper wires communication n Twisted Pairn Allows a bit stream to be transported n UTP – Unshielded Twisted Pair STP - Shielded Twisted Pair from one machine to another n Coaxial cables Can be categorised as nn n Guided media n Fibre n Unguided media 1
Unguided media Twisted pairn Radio waves n Pairs of insulated copper wires twistedn Microwave links together n for the reduction of Electro Magneticn IR – Infra Red Interference n Covered with an outer insulating jacket n Two types n Shielded twisted-pair (STP) n Unshielded twisted-pair (UTP)Twisted pair cont… STP & UTPn One or more pairs of wiren Twisted around one anothern Resistant to interferencen A parallel set of wires forms an antenna but twisted pair does notn Limits signals influence on other pair n Referred as CrosstalkUTP Pros & Consn UTP cables are grouped in several n Inexpensive categorises n Easy to work with n Category 1 – Voicegrade telephone cabling n Can run up to several Kilometres n Category 2 – up to 4 Mbps 4 pairs without amplification n Category 3 – up to 10 Mbps 4 pairs n For long distances repeaters are needed Category 4 – up to 16 Mbps 4 pairs n n With the distance bandwidth reduces n Category 5 – up to 100 Mbps 4 pairs Category 5e – up to 1 Gbps 4 pairs n High number of twists per meter reduces the crosstalk n 2
Coaxial cables Types of cablesn In early days of networking these types n 50 O - Baseband Coaxial Cable of cables were heavily used n Used in digital transmission n 75 O - Broadband Coaxial Cable n Used for analog transmission n Used for TV antennas & Cable TVAdvantages of Coaxial cables Disadvantages of Coaxial cablesn Easy to install n Higher cost compared to twisted pairn Inexpensive n Harder to work with & cable easily getn Since it is shielded can span a higher damaged distance at higher speed than twisted pairn High bandwidthn Excellent noise immunityFibre optics Fibre optics cont…n Bundle of glass or plastic fibresn Sends signals on pulses of light n Based on the concept of Total Internal Reflectionn Immune to Electro Magnetic & other interferencesn High bandwidth, speed, long distance 3
Components of a fibre system Components of a fibre system cont… n Light source n Light Source n Transmission medium n Converts electrical signals to optical signals n Light detector n Transmission Medium n Transmits the light signal from one point to another n Detector n Detects the light signal & converts it back to electrical signalsLight source Light detector Types of fibre Types of fibre cont… Jacket (Plastic) Core (Glass) n Single Mode fibre n Harder to manufactory so high cost n High speed Single Mode fibre n Long distance (up to 100Km) n Multi Mode fibre Cladding (Glass) n Low cost n Low speed n Lower distance (2 Km) Multi Mode fibre Radio Transmission Wireless Networking n Unguided transmission - Intangible media n Use is increasing with the introduction n Easy to generate of mobile devices n Travel long distances n Cost is decreasing n Penetrate buildings easily n Hybrid networks use cable & wireless n Omni directional n At high frequencies they travel in straight lines n Absorbed by rain n Reflected by ionosphere 4
Wireless LAN Technologies Infrared (IR)n Infrared (IR) n Uses IR signals transmit datan Laser or light wave n Used for short range communication n Do not pass through solid objectsn Microwave Transmission n Simple to develop & cost effectiven Satellite Communications n Low speed n Cannot be used outdoor n Used in remote controllers, hand held devices, laptops, etc.Light wave Transmission Microwave Transmissionn Can be used to interconnect LANs in 2 n Above 100MHz, waves travel in straight lines different buildings n Can be narrowly focusedn Highly focused & coherent n Can be concentrated to a small beam using parabolic antennaen Requires very high degree of alignment n Antennas at transmitter & receiver must be between transmitter & detector aligned (Line of Sight)n Cannot penetrate rain or thick fog n Long distance links must have repeaters n Does not penetrate through objectsSatellite Communication UTP Cat 5e Cablesn Make use of geosynchronous Satellites n Used with 10/100/1000 Ethernet n Orbiting the earth at a distance of 36000 n Most heavily used cabling types km above the equator n Are connected to networking devicesn Period of the satellite is 24 hours through RJ45 Jacksn Uses different bands for different purposes n Telecommunication, TV braodcasting 5
RJ45 cabling Types of RJ45 cablingn Has 8 wires n Straight Cablesn But only 4 are used n Cross Cables n 2 for transmitting data n Rollover cables n 2 for receiving data Straight Cable Cross Cable Wire pairs 6