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Digital Transmission Lecture o3 Advanced Computer Networks (ACN) 545

Mr. Thilak de Silva. BSc. Eng., MSc, CEng, FIE(SL), FIET(UK), CITP(UK), MBCS(UK), MIEEE (USA). Digital Transmission Lecture o3 Advanced Computer Networks (ACN) 545. Today's Agenda. Jitter Digital to Digital Conversion Line coding Block coding Scrambling Analog to Digital Conversion.

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Digital Transmission Lecture o3 Advanced Computer Networks (ACN) 545

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  1. Mr. Thilak de Silva. BSc. Eng., MSc, CEng, FIE(SL), FIET(UK), CITP(UK), MBCS(UK), MIEEE (USA) Digital TransmissionLecture o3Advanced Computer Networks (ACN) 545 M.Sc. in IT - Year 1 Semester II - 2012

  2. Today's Agenda • Jitter • Digital to Digital Conversion • Line coding • Block coding • Scrambling • Analog to Digital Conversion M.Sc. in IT - Year 1 Semester II - 2012

  3. Session Outcomes • At the end of this session you will have a broad understanding of Digital to Digital conversion and Analog to Digital Conversion of signals. M.Sc. in IT - Year 1 Semester II - 2012

  4. Jitter – (Digital impairments) • All data packets may not follow the same route. • Due to delays (in routers, media etc) different data packets reach the destination at different times. • Then jitter occurs. • Is vital in multimedia applications. M.Sc. in IT - Year 1 Semester II - 2012

  5. Digital To Digital Conversion • Line coding – converting digital data into a digital signal that can be transmitted through a transmission media. • Data elements – what we need to send • Signal elements – what we can send • Signal elements are the carriers who carries data elements. M.Sc. in IT - Year 1 Semester II - 2012

  6. Signal elements and Data elements Ratio (r)= Data elements Signal elements Source - http://train-srv.manipalu.com/wpress/wp-content/uploads/2011/10/clip-image0044-thumb4.jpg M.Sc. in IT - Year 1 Semester II - 2012

  7. Types of Line Coding • Unipolar - NRZ • Polar – NRZ,RZ and biphase(Manchester and differential Manchester) • Bipolar-AMI and pesudoternary • Multilevel – 2B/1Q , 8B/6T and 4D-PAM5 • Multitransition – MLT 3 M.Sc. in IT - Year 1 Semester II - 2012

  8. Example 8B/6T • 8 binary values in 6 signals • Additional Combinations = 729 – 256 = 473 M.Sc. in IT - Year 1 Semester II - 2012

  9. Example 8B/6T Why extra combinations? • 256 number of combinations are already defined and if there are any undefined combinations, that means there is a error. • Having additional combinations leads to easy error detection at the receiving end M.Sc. in IT - Year 1 Semester II - 2012

  10. Line coding • Every line coding schema should have, • Error Detection and • Self Synchronization (done by PLL) • PLL will not Operate if there are no state changes • Eg: All 0 s in RZ M.Sc. in IT - Year 1 Semester II - 2012

  11. All Media has Characteristic Impedance • R -  resistance per unit length, • L -  inductance per unit length, • G -  conductance of the dielectric per unit length, • C  - capacitance per unit length, • j  -  imaginary unit, and • ω  -  angular frequency. Source :http://www.google.lk/imgres?imgurl=http://upload.wikimedia.org/wikipedia/commons/thumb/1/11/Transmission_line_element.svg/220px-Transmission_line_element.svg.png&imgrefurl=http://en.wikipedia.org/wiki/Characteristic_impedance&usg=__mIMtU47Cbk5Fjqt5yYJ1BPgoJYI=&h=134&w=220&sz=4&hl=en&start=1&zoom=1&tbnid=_6PLMVwREZh4GM:&tbnh=65&tbnw=107&ei=n6kmT_6EE87NrQf8lvyoCA&prev=/search%3Fq%3Dcharacteristic%2Bimpedance%26hl%3Den%26gbv%3D2%26tbm%3Disch&itbs=1 M.Sc. in IT - Year 1 Semester II - 2012

  12. Characteristic Impedance contd.. • Because of capacitor signal gets charged, • In Manchester coding it gets charged to a some extent and remains. • We need to have a way of discharging DC component, (avg =0), Eg: AMI M.Sc. in IT - Year 1 Semester II - 2012

  13. Block Coding – mB/nB • Changes a block of m bits into a block of n bits. (n>m) • Eg: • 4B/5B coding – 4 bits converted to 5 bits (32-16 = 16 number of redundant combinations) • 8B/10B – 8 bits are converted to 10 bits M.Sc. in IT - Year 1 Semester II - 2012

  14. Block coding and Line coding Block Coding Line coding DATA Transmission media Sender For Error detection Convert data to signal Block Coding DATA Line coding Receiver M.Sc. in IT - Year 1 Semester II - 2012

  15. Scrambling • Long sequence of zeros (0) are converted into a combination of bits. 000000 010110 • Mainly for synchronization. • Useful to achieve security. • Eg: • B8ZS • HDB3 M.Sc. in IT - Year 1 Semester II - 2012

  16. Analog to Digital Conversion • Converting an Analog signal to a Digital signal. • Used in telephone systems to convert the voice signal to digital signal. • Eg: • Pulse Code Modulation • Delta Modulation • Adaptive Delta Modulation M.Sc. in IT - Year 1 Semester II - 2012

  17. References • Data Communications and Networking, Forouzan, Chapter 04, 4th Edition M.Sc. in IT - Year 1 Semester II - 2012

  18. Thank You… M.Sc. in IT - Year 1 Semester II - 2012

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