Welcome! Operating Systems and Networks • Brief introduction of lecturer and TAs – Adrian Perrig, Professor in Department of Computer Science, Director of Network Security Group – Exercise sessions: David Barrera (PhD), Raphael Reischuk (PhD) – Labs / homeworks: Tae-Ho Lee, Chris Pappas Networks Part 1: Introduction – Network security group research area: design and implementation of secure future Internet architecture (SCION project http://www.scion-ar c hit e ct ur e .ne t ) Adrian Perrig Network Security Group ETH Zürich 2 Course Structure Lecture Style • Lectures • Student interaction is encouraged! • Homework – Please ask questions if something is unclear • Projects – Please point out any errors that you spot – • Exercise sessions Please focus on lecture instead of facebook, twitter, etc. • Quizzes • Please turn off cell phone and Wi F i during class 3 4 Minds open… … Laptops closed and cell phones / ipads off 6 Textbook and Slide Credit Problems with Being On-line During Class • Textbook: TANENBAUM, ANDREW S.; WETHERALL, DAVID J., COMPUTER NETWORKS, 5th Edition, 2011. • It takes the mind a few minutes to reach a state of deep • Slides adapted from slide deck by David Wetherall concentration • Lecture video at: – Reaching deep concentration needs to be trained, many people http://media.pearsoncmg.com/ph/streaming/esm/tanenbaum5e_videon have lost this ability due to constant / frequent interruptions otes/tanenbaum_videoNotes.html • Knowing that one cannot be interrupted increases concentration. Said another way: Expectation of interruption prevents deep concentration – Try to be off-line when studying networking! • Open laptop / iPad / cell phone used for surfing can also disrupt / interrupt people sitting behind you 7 Highly Recommended as Reference Also recommended • Larry L. Peterson and Bruce S. • Kevin R. Fall and W. Davie: Richard Stevens: “Computer Networks: A Systems Approach” “TCP/IP Illustrated, • 5th Edition Volume 1: The Protocols” • 2nd Edition, 2011 9 Also recommended Study Recommendations Computer Networking: A Top-Down Approach: Kurose and Ross • Make list of acronyms, concepts 5th Edition • Read corresponding sections in text book – Available in INFK library • Participate in exercise sessions, solve homework, Srinivasan Keshav: and DO THE PROJECTS! An Engineering Approach to Computer Networking 11 12 Homework Assignment Presentations Projects • We will have 2 hands-on projects • Assignments are posted at the end of each week and presented in the following week – Reliable communication – Routing • Projects are completed in groups of 3-4 students – Register at http://bit.ly/22OxK0S – First project will be posted by Friday midnight on course web page and presented next week 13 14 Final Grade Focus of the course • Projects & Exercises are optional – but highly recommended to do them • Networking grade = exam grade ??? • Final grade = average( Networking grade, OS grade ) 15 16 Focus of the course (2) The Main Point • Three “networking” topics: 1. To learn how the Internet works – What really happens when you “browse the web”? Distributed systems – What are TCP/IP, DNS, HTTP, NAT, VPNs, 802.11 etc. anyway? Networking 2. To learn the fundamentals of computer networks Communications • We mainly study the Networking aspects 17 18 Why learn about the Internet? From this experimental network … 1. Curiosity ARPANET ~1970 2. Understand how the system works we’re spending most of our time with – Interesting statistic: we’re spending more time online than sleeping! 3. Impact on our world (a) Dec. 1969. (b) July 1970. (c) March 1971. 4. Job prospects! 19 20 To this! Internet – Societal Impact Internet ~2005 • An enabler of societal change • An everyday institution – Easy access to knowledge used at work, home, – Electronic commerce and on-the-go – Personal relationships • Visualization contains – Discussion without censorship millions of links Attribution: By Th e Op te Project [CC-BY-2.5], vi a W i ki med i a C o mmo n s 21 22 Internet – Economic impact The Main Point (2) 1. To learn how the Internet works • An engine of economic growth 2. To learn the fundamentals of computer – Advertising-sponsored search networks – Online stores – What hard problems must they solve? – Online marketplaces – Crowdsourcing – What design strategies have proven valuable? 23 24 Why learn the Fundamentals? Fundamentals – Intellectual Interest 1. Apply to all computer networks • Example key problem: Reliability! – Any part of the Internet might fail 2. Intellectual interest – Messages might be corrupted – How to create a reliable network out of unreliable 3. Change / reinvention components? 4. Pass this course :-) • Reliability solutions – Codes to detect/correct errors – Routing around failures ... 25 26 Fundamentals – Intellectual Interest (2) Fundamentals – Reinvention Key problem Example solutions • The Internet is constantly being re-invented! Reliability despite Codes for error detection/correction (§3.2, 3.3) – Growth over time and technology trends drive failures Routing around failures (§5.2) Network growth Addressing (§5.6) and naming (§7.1) upheavals in Internet design and usage and evolution Protocol layering (§1.3) • Today’s Internet is different from yesterday’s Allocation of resources Multiple access (§4.2) like bandwidth Congestion control (§5.3, 6.3) – And tomorrow’s will be different again Security against Confidentiality of messages (§8.2, 8.6) – But the fundamentals remain the same various threats Authentic ation of communicating parties (§8.7) 27 28 Fundamentals – Reinvention (2) Fundamentals – Reinvention (3) • Examples of upheavals in the past 1-2 decades • Currently around 1.1 billion Growth / Tech Driver Upheaval Internet hosts … Emergence of the web Content Distribution Networks Digital songs/videos Peer-to-peer file sharing Falling cost/bit Voice-over-IP cal li ng Many Internet hosts IPv6 Wireless advances Mobile devices 29 30 Not a Course Goal Example Uses of Networks • Work: • To learn IT job skills – Email, file sharing, printing, … – How to configure equipment • Home: • E.g., Cisco certifications – Movies / songs, news, calls / video / messaging, e- – But course material is relevant, and we use hands-on commerce, What do these uses tell us about … tools • Mobile: why we build networks? – Calls / texts, games, videos, maps, information access … 31 32 For User Communication For Resource Sharing • • From the telephone onwards: Many users may access the same underlying resource – VoIP (voice-over-IP) – E.g., 3D printer, search index, machines in the cloud – Video conferencing →More cost effective than dedicated resources per user – Instant messaging – – Social networking Even network links are shared via statistical multiplexing →Enables remote communication – Need low latency for interactivity 33 34 Statistical Multiplexing Statistical Multiplexing (2) • Sharing of network bandwidth between users according • Example: Users in an ISP network 5 to the statistics of their demand – Network has 10 0 Mbps (units of bandwidth) 100 . – (Multiplexing just means sharing) – Each user subscribes to 5 Mbps, for videos ISP 5 – Useful because users are mostly idle and their traffic is bursty – But a user is active only 50% of the time … 5 • How many users can the ISP support? • Key question: – With dedicated bandwidth for each user: – How much does it help? – Probability all bandwidth is used: (assuming independent users) 35 36 Statistical Multiplexing (3) For Content Delivery • With 30 independent users, still unlikely (2% chance) to • Same content is delivered to many users need more than 100 Mbps! – Videos (large), songs, apps and upgrades, web pages, – Binomial probabilities … → Can serve more users with the same size network – Statistical multiplexing gain is →More efficient than sending a copy all the way to 30/20 or 1.5X each user – But may get unlucky; users will have degraded service – Uses replicas in the network 37 38 Content Delivery (2) Content Delivery (3) • Sending content from the source to 4 users takes 4 x 3 = • But sending content via replicas takes only 4 + 2 = 6 12 “network hops” in the example “network hops” User User . Source Source Replica User User 39 40 For Computer Communication To Connect Computers to the Physical World • To let computers interact with other computers • For gathering sensor data, and for manipulating the – E.g., e-commerce, backup, cloud computing world – E.g., webcams, location on mobile phones, door locks, … →Enables automated information processing across different parties • This is a rich, emerging usage (IoT: Internet of Things) 41 42 The Value of Connectivity The Value of Connectivity (2) • “Metcalfe’s Law” ~1980: Bob Metcalfe • Example: both sides have 12 nodes, but the left network – The value of a network of N nodes is has more connectivity proportional to N2 – Large networks are relatively more valuable than small ones vs + 66 connections 15 connections 15 connections : © 2009 IEEE 43 44 Parts of a Network Component Names Component Function Example application Applic ation, or app, user Uses the network Skype, iTunes, Amazon Host, or end-system, edge Supports apps Laptop, mobile, desktop device, node, source, sink Router, or switc h, node, Relays messages Access point, cable/DSL hub, intermediate system between links modem router link host Link, or c hannel Connects nodes Wires, wireless 45 46 Types of Links Wireless Links • Message is broadcast • Full-duplex – – Bidirectional Received by all nodes in range – Not a good fit with our model • Half-duplex – Bidirectional