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Introduction Outline to n Terminology Data Communication n Transmission medium by rfb16446


									            Introduction                       Outline
                 to                            n   Terminology
        Data Communication                     n   Transmission medium
                                                   n   Guided media
                                                       Unguided media
        DCS201- Computer Science

                              Dilum Bandara

Data Communication                             Terminology
n   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,
                                               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 medium

Transmission Medium                            Guided media
n   Provides the path for data                 n   Copper wires
    communication                                  n   Twisted Pair
n   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

    n   Guided media
                                               n   Fibre
    n   Unguided media

Unguided media                                      Twisted pair
n   Radio waves                                     n   Pairs of insulated copper wires twisted
n   Microwave links                                     together
                                                        n   for the reduction of Electro Magnetic
n   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 & UTP
n   One or more pairs of wire
n   Twisted around one another
n   Resistant to interference
n   A parallel set of wires forms an antenna
    but twisted pair does not
n   Limits signals influence on other pair
    n   Referred as Crosstalk

UTP                                                 Pros & Cons
n   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   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

Coaxial cables                                   Types of cables
n   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 TV

Advantages of Coaxial cables                     Disadvantages of Coaxial cables
n   Easy to install                              n   Higher cost compared to twisted pair
n   Inexpensive                                  n   Harder to work with & cable easily get
n   Since it is shielded can span a higher           damaged
    distance at higher speed than twisted
n   High bandwidth
n   Excellent noise immunity

Fibre optics                                     Fibre optics cont…
n   Bundle of glass or plastic fibres
n   Sends signals on pulses of light
    n   Based on the concept of Total Internal
n   Immune to Electro Magnetic & other
n   High bandwidth, speed, long distance

       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
                                                                n   Detector
                                                                        n   Detects the light signal & converts it back to
                                                                            electrical signals
Light 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

Wireless LAN Technologies                               Infrared (IR)
n   Infrared (IR)                                   n   Uses IR signals transmit data
n   Laser or light wave                             n   Used for short range communication
                                                    n   Do not pass through solid objects
n   Microwave Transmission
                                                    n   Simple to develop & cost effective
n   Satellite Communications
                                                    n   Low speed
                                                    n   Cannot be used outdoor
                                                    n   Used in remote controllers, hand held
                                                        devices, laptops, etc.

Light wave Transmission                                 Microwave Transmission
n   Can be used to interconnect LANs in 2           n   Above 100MHz, waves travel in straight lines
    different buildings                             n   Can be narrowly focused
n   Highly focused & coherent                       n   Can be concentrated to a small beam using
                                                        parabolic antennae
n   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 objects

Satellite Communication                                 UTP Cat 5e Cables
n   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 devices
n   Period of the satellite is 24 hours                     through RJ45 Jacks
n   Uses different bands for different
    n   Telecommunication, TV braodcasting

    RJ45 cabling                  Types of RJ45 cabling
n   Has 8 wires                   n   Straight Cables
n   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


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