06/04/17 Welcome! Operang Systems and Networks • Brief introduc-on of lecturer and TAs – Adrian Perrig, Professor in Department of Computer Science, Director of Network Security Group – Teaching assistants: Tae-Ho Lee, Chris Pappas, Laurent Chuat Networks Part 1: Introduc-on – Network security group research area: design and implementaon of secure future Internet architecture (SCION project hp://www.scion- architecture.net) Adrian Perrig Network Security Group ETH Zürich 2 Course Structure Lecture Style • Lectures • Student interac-on is encouraged! • Homework – Please ask ques-ons if something is unclear • Exercise sessions – Please point out any errors that you spot – • Quizzes Please focus on lecture instead of Facebook, TwiUer, etc. • Please turn off your phone and other devices during class 3 4 Minds open… … Laptops closed and cell phones / ipads off 6 1 06/04/17 Textbook and Slide Credit Problems with Being Online During Class • Textbook: TANENBAUM, ANDREW S.; WETHERALL, DAVID j., COMPUTER NETWORKS, 5th Edi-on, 2011. • It takes the mind a few minutes to reach a state of deep • Slides adapted from slide deck by David Wetherall concentraon • Lecture video at: hUp://media.pearsoncmg.com/ph/streaming/esm/ – Reaching deep concentraon needs to be trained, many people tanenbaum5e_videonotes/tanenbaum_videoNotes.html have lost this ability due to constant / frequent interrup-ons • Knowing that one cannot be interrupted increases concentraon. Said another way: Expectaon of interrup-on prevents deep concentraon – Try to be off-line when studying networking! • Open laptop / iPad / cell phone used for surfing can also disrupt / interrupt people sing 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 Edion Volume 1: The Protocols” • 2nd Edion, 2011 9 Also recommended Study Recommendaons Computer Networking: A Top-Down Approach: Kurose and Ross • Make list of acronyms, concepts 5th Edi-on • Read corresponding sec-ons in text book – Available in INFK library • Par-cipate in exercise sessions, solve homework, Srinivasan Keshav: and DO THE PROjECTS! An Engineering Approach to Computer 11 Networking 12 2 06/04/17 Quizzes Final Grade • Extra credit!!! • 5 Quizzes in total • Exercises are op-onal – during lecture (at the beginning or end) – but highly recommended to do them – 10 minutes max. – not announced at the previous lecture • Quizzes do not harm your grade – about the previously taught set of lecture slides – highly recommended to aend class • Each quiz 1 point: • Networking grade = exam grade + quiz grade – 0.2 points for par-cipaon • Final grade = average( Networking grade, OS grade ) – 4 ques-ons x 0.2 points 13 14 Focus of the course Focus of the course (2) • Three “networking” topics: Distributed systems ??? Networking Communicaons • We mainly study the Networking aspects 15 16 The Main Point Why learn about the Internet? 1. To learn how the Internet works 1. Curiosity – What really happens when you “browse the web”? – What are TCP/IP, DNS, HTTP, NAT, VPNs, 802.11 etc. 2. Understand how the system works we’re spending anyway? most of our -me with – Interes-ng stas-c: we’re spending more -me online 2. To learn the fundamentals of computer networks than sleeping! 3. Impact on our world 4. job prospects! 17 18 3 06/04/17 From this experimental network … To this! ARPANET ~1970 Internet ~2005 • An everyday ins-tu-on used at work, home, and on-the-go • Visualizaon contains (a) Dec. 1969. (b) July 1970. (c) March 1971. millions of links Aribu-on: By The Opte Project [CC-BY-2.5], via Wikimedia Commons 19 20 Internet – Societal Impact Internet – Economic impact • An enabler of societal change • An engine of economic growth – Easy access to knowledge – Adver-sing-sponsored search – Electronic commerce – Online stores – Personal relaonships – Online marketplaces – Discussion without censorship – Crowdsourcing 21 22 The Main Point (2) Why learn the Fundamentals? 1. To learn how the Internet works 1. Apply to all computer networks 2. To learn the fundamentals of computer 2. Intellectual interest networks – What hard problems must they solve? 3. Change / reinven-on – What design strategies have proven valuable? 4. Pass this course :-) 23 24 4 06/04/17 Fundamentals – Intellectual Interest Fundamentals – Intellectual Interest (2) • Example key problem: Reliability! Key problem Example soluons – Any part of the Internet might fail Reliability despite Codes for error detec-on/correc-on (§3.2, 3.3) – Messages might be corrupted failures Rou-ng around failures (§5.2) – How to create a reliable network out of unreliable Network growth Addressing (§5.6) and naming (§7.1) components? and evolu-on Protocol layering (§1.3) Allocaon of resources Mul-ple access (§4.2) • Reliability solu-ons like bandwidth Conges-on control (§5.3, 6.3) – Codes to detect/correct errors Security against Confiden-ality of messages (§8.2, 8.6) – Rou-ng around failures ... various threats Authen-caon of communicang par-es (§8.7) 25 26 Fundamentals – Reinven-on Fundamentals – Reinven-on (2) • The Internet is constantly being re-invented! • Currently around – Growth over -me and technology trends drive 1.1 billion upheavals in Internet design and usage Internet hosts … • Today’s Internet is different from yesterday’s – And tomorrow’s will be different again – But the fundamentals remain the same 27 28 Fundamentals – Reinven-on (3) Not a Course Goal • Examples of upheavals in the past 1-2 decades • To learn IT job skills Growth / Tech Driver Upheaval – Emergence of the web Content Distribu-on Networks How to configure equipment Digital songs/videos Peer-to-peer file sharing • E.g., Cisco cer-ficaons Falling cost/bit Voice-over-IP calling – But course material is relevant, and we use hands-on Many Internet hosts IPv6 tools Wireless advances Mobile devices 29 30 5 06/04/17 Example Uses of Networks Example Uses of Networks • Work: • Work: – Email, file sharing, prin-ng, … – Email, file sharing, prin-ng, … • Home: • Home: – Movies / songs, news, calls / video / messaging, e- – Movies / songs, news, calls / video / messaging, e- commerce, … commerce, … What do these uses tell us about • Mobile: • Mobile: why we build networks? – Calls / texts, games, videos, maps, informaon access … – Calls / texts, games, videos, maps, informaon access … 31 32 For User Communicaon 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 effec-ve than dedicated resources per user – Instant messaging – – Social networking Even network links are shared via stas-cal mul-plexing →Enables remote communicaon – Need low latency for interac-vity 33 34 Stas-cal Mul-plexing Stas-cal Mul-plexing (2) • Sharing of network bandwidth between users according • Example: Users in an ISP network 5 to the stas-cs of their demand . – Network has 100 Mbps (units of bandwidth) 100 ISP – (Mul-plexing just means sharing) – Each user subscribes to 5 Mbps, for videos 5 – – Useful because users are mostly idle and their traffic is bursty But a user is ac-ve only 50% of the -me … 5 • How many users can the ISP support? • Key ques-on: – With dedicated bandwidth for each user: – How much does it help? – Probability all bandwidth is used: (assuming independent users) 35 36 6 06/04/17 Stas-cal Mul-plexing (3) For Content Delivery • With 30 independent users, s-ll unlikely (2% chance) to • Same content is delivered to many users need more than 100 Mbps! – Binomial probabili-es – Videos (large), songs, apps and upgrades, web pages, … → Can serve more users with the same size network – Stas-cal mul-plexing 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 Communicaon To Connect Computers to the Physical World • To let computers interact with other computers • For gathering sensor data, and for manipulang the – E.g., e-commerce, backup, cloud compu-ng world – E.g., webcams, locaon on mobile phones, door locks, … → Enables automated informaon processing across different par-es • This is a rich, emerging usage (IoT: Internet of Things) 41 42 7 06/04/17 The Value of Connec-vity The Value of Connec-vity (2) • “Metcalfe’s Law” ~1980: Bob Metcalfe • Example: both sides have 12 nodes, but the le€ network – The value of a network of N nodes is has more connec-vity propor-onal to N2 – Large networks are relavely more valuable than small ones vs + 66 connecons 15 connecons 15 connecons : © 2009 IEEE 43 44 Parts of a Network Component Names Component Func0on Example applicaon Applicaon, 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 switch, node, Relays messages Access point, cable/DSL router hub, intermediate system between links modem host link Link, or channel Connects nodes Wires, wireless 45 46 Types of Links Wireless Links • Message is broadcast • Full-duplex – Received by all nodes in range – Bidirec-onal – Not a good fit with our model • Half-duplex