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Mr. Thilak d e 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

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Mr thilak d e silva bsc eng msc ceng fie sl fiet uk citp uk mbcs uk mieee usa

Mr. Thilakde 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


Today s agenda
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


Session outcomes
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


Jitter digital impairments
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


Digital to digital conversion
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


Signal elements and data elements
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


Types of line coding
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


Example 8b 6t
Example 8B/6T

  • 8 binary values in 6 signals

  • Additional Combinations = 729 – 256 = 473

M.Sc. in IT - Year 1 Semester II - 2012


Example 8b 6t why extra combinations
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


Line coding
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


All media has characteristic impedance
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


Characteristic impedance contd
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


Block coding mb nb
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


Block coding and line coding
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


Scrambling
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


Analog to digital conversion
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


References
References

  • Data Communications and Networking, Forouzan, Chapter 04, 4th Edition

M.Sc. in IT - Year 1 Semester II - 2012


Thank you

Thank You…

M.Sc. in IT - Year 1 Semester II - 2012


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