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A bit about myself I'm a physicst by training and didn't "become" a computer COMPSCI 314 S2C scientist until my PhD Modern Data Communications Have taught in this department since 2000 Have been involved in a wide variety of

  1. A bit about myself • I'm a physicst by training and didn't "become" a computer COMPSCI 314 S2C scientist until my PhD Modern Data Communications • Have taught in this department since 2000 • Have been involved in a wide variety of courses ranging Ulrich Speidel from application development, data communication, Internet programming and introductory programming to ulrich@cs.auckland.ac.nz computer architecture • I'm quite an approachable person & just because I happen to have my door closed in 303S.594, it doesn't mean I'm trying to hide from you  7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 2 2 Why I teach this course Course structure • My interest in electronic communication started as a teenager – • Week 1 ‐ 4: Technical foundations and limits of data somewhat unusually with an aeronautical radiotelephone communication: channels, signals, codes operator's certificate at age 16 Lecturer: Ulrich Speidel • I then became interested in amateur radio, obtained a license and was active in Germany, Australia, and later in New Zealand • Week 5 ‐ 8: Nevil Brownlee • Became involved quite heavily in packet radio (a kind of amateur radio predecessor of Wi ‐ Fi) • Week 9 ‐ 12: Aniket Mahanti • Have since worked with all layers of the communication stack – from the physical layer (cable, radio, fibre…) to the applications (web) in both theory and practice 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 3 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 4

  2. Office hours Assignments and Test • Open door policy in 303S.594 • I will set one assignment, due at 12:00 noon, Monday 10 August 2015 • If you want an appointment, contact me on ulrich@cs.auckland.ac.nz • Nevil and Aniket will also set one assignment each • The mid ‐ semester test will be held during lecture time on September 18, 2015 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 5 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 6 Communication with me Other things Don't be shy to approach me! Here's how to get a meaningful answer quickly… • • I expect you to read your Computer Science e ‐ mail • Put "COMPSCI314" in the subject of your e ‐ mail on a question that relates to COMPSCI314 regularly (i.e., at least once a day) – or risk being mistaken for a 280 student! • Announcements made via e ‐ mail are expected to Try to be as concise as possible in your question. It doesn't need to be as short as a text • message. It helps if you refer to slide numbers, assignment questions, etc. be known to you 24 hours after they have been • I may anonymise your question and cc the rest of the class into my answer if I think it's of made interest to others. Check and keep your class e ‐ mail – it'll often already contain the answer you're looking for. • Please see our tutor first if you have questions • Note that around assignment due dates, tests and exams, I often get lots of questions by e ‐ mail. Checking your past class e ‐ mail is often a faster way to get an answer! • Get in early and don't wait to the last minute if you need help. 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 7 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 8 7

  3. What I'll cover – what you'll learn Our textbook • Theme 1: Physical foundations of data • “Computer Networking: A Top ‐ Down Approach”, 5 th or 6th edition, by J.F. Kurose and K.W. Ross, communications Pearson Education • Data can travel across many media: cables, radio links – and each medium has its own special properties • Won't use this textbook in my part, but you might • You'll learn about signals and the way we can express them in the physical world: want to get it now for Nevil's & Aniket's parts electrical, optical, radio, … • You'll develop an understanding of concepts such as latency, bandwidth, noise, bit rates, baud rates, and bit error rates, and how they relate to each other 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 9 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 10 What I'll cover – what you'll learn Week 1 • Theme 2: Channels and codes • Lecture 1: What's a signal? Electrical and optical signals • In this theme, we'll learn about the characteristics of different channels and how we can package data for transport, so it gets to • Lecture 2: Radio signals, signal propagation, the receiver with as few errors and as little resource use as possible decibels • You'll develop an understanding of different channel types, where you'll likely to encounter them, and how information is coded and handled to deal with the requirements of each channel • Lecture 3: Satellite communication, communication channels and Fourier analysis, the concept of bandwidth 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 11 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 12

  4. Signals ‐ generally Lecture 1 • What is a signal? “Potential”: • Electrical signals …could be the brightness of the light in an optical fibre …could be the voltage in an electric conductor …or, the level of water in a tank! • Optical signals 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 13 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 14 Potential Potential difference in potential difference in potential Can define this difference Difference now “negative as “positive”(left tank has (“right tank has higher higher water level than right water level than left tank, tank, i.e., water will flow to i.e., water will flow to the the right) left) 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 15 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 16

  5. Potential and electrical signals Potential • Think about electrical conductors as water tanks with water in them, with the water molecules being electrons • Introducing signals means changing the water levels in one or more of the tanks – pressure on valves or flow no difference in potential into other tanks results • The water pressure (potential) is the voltage No difference (“equipotential state” or “equilibrium”) means • The water flow (litres per second) is the current no water will flow. Note that this state is possible for arbitrary fill levels 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 17 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 18 Types of (electrical) signals Power • Water that flows through a device such as a turbine can do work for us, e.g., generate energy . In physics, (the ability to perform) work and energy are the same. Analog signals: potential changes continuously with time To perform work, we need both water pressure (voltage) and water flow (current). • • In communication, we often use analog signals that are Current across a load such as a turbine can only perform work if it is driven by pressure. • limited in amplitude (certain minimal and maximal voltages and/or currents are not exceeded) and that alternate between The amount of energy that can be created in a given amount of time is therefore • positive and negative voltages/currents proportional to the square of the water pressure (or square of the voltage) • Such signals may be thought of as the superposition of a amplitudes, frequencies, and phases of sinusoidal signals • The amount of energy that can be transferred between systems per second is known as power and is measured in watts. (Fourier theorem) • we’ll come back to that in a moment! 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 19 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 20

  6. Analog signal parameters Digital signals • Digital signals are a special case of analog signals Amplitude • Ideally, they only have two discrete states, 0 and 1 Phase • These may be expressed, e.g., as two different voltage levels or light intensities DC Offset • Transitions between 0 and 1 and vice versa are in theory instantaneous. That is, a digital system should never be in an “inbetween” state • In practice, this is not possible. This fact causes a lot of problems! We’ll soon learn that sinusoidal signals can be used to compose any other signal! 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 21 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 22 Digital vs. analog signals Digital vs. analog signals (II) • Analog signal communication does not necessarily • Both digital and analog signals can be used to convey require a computer or digital logic! information • Analog signals are used for: conventional telephone, • Analog signal communication cannot separate some older mobile phones, conventional radio and TV, as signal from noise auxiliary carriers for some digital communication • Digital signal communication requires some sort of • Digital signals are used for: data communication, digital processor (more effort) including most mobile phones and digital radio/TV • Digital signal communication can separate signal from noise 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 23 7/20/2015 COMPSCI 314 S2C 2014 Ulrich Speidel 24

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