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Course Overview

Spring 2012 ECE/CS 372 Introduction to Computer Networks Lecture 1 School of Electrical Engineering and Computer Science Oregon State University. Course Overview. Lecture/Office/Lab Hours. Course website http://web.engr.oregonstate.edu/~qassim/index_files/ComputerNetworks.htm

harlan-briggs
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Course Overview

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  1. Spring 2012 ECE/CS 372 Introduction to Computer Networks Lecture 1 School of Electrical Engineering and Computer Science Oregon State University Course Overview Chapter 1, slide:

  2. Lecture/Office/Lab Hours • Course website • http://web.engr.oregonstate.edu/~qassim/index_files/ComputerNetworks.htm • Please write down this URL—all course material and information will be provided thru this site • Lectures • Everyday 1-1:50pm • Instructor • Yousef Qassim (qassim@eecs.oregonstate.edu) • Office hours: TR 2:30-3:20pm @KEC lounge Chapter 1, slide:

  3. Lecture/Office/Lab Hours • Lab Assistant • Location: Dearborn 205 • Lab hours: to help you with your labs 205 DEAR Information can be found in course’s website • Lab • Location: Dearborn 205 • Access code: will be written on board Chapter 1, slide:

  4. Prerequisite/Textbook Prerequisite: • CS or ECE 271 or an equivalent course • Basic Linux familiarity Textbook • Textbook is Required • Computer Networking: A Top-Down Approach Featuring the Internet, 6th Edition, Games F. Kurose, Keith W. Ross Chapter 1, slide:

  5. Grading Policy • Assignments: 15% • Each student must hand in one copy • 5 assignments: approx. 1 every two weeks • Labs: 15% • Each student must hand in one copy • 5 labs: approx. 1 every two weeks • One midterm exam: 30% • Final exam: 40% Chapter 1, slide:

  6. Topics To Be Covered • Architecture of the Internet, and network protocols • Delay analysis • Packet-switching and circuit-switching • Congestion and flow control: TCP • Routing algorithms: IP and datagram • Data link layers and Ethernet: ARP, CSMA/CD • Medium access control and local area networks Chapter 1, slide:

  7. Lectures & assignments Objective • Deep understanding of basic and fundamental networking concepts, architectures, and philosophies • IMPORTANT: this course is NOT about setting up your router at home, or writing a twitter program!! Approach: how to do well in this course • Easy: attend ALL lectures and do ALL assignments • Do your assignments individually • Do NOT miss any Bonus Quiz (i.e., do not miss class) • Some hw problems will be solved in class: this gives you the opportunity to clarify things further Chapter 1, slide:

  8. Labs Objective • Understand how Internet protocols work • Force network protocols to perform certain actions • Observe and analyze protocols’ behavior Approach • Software tool: Wireshark • already installed in Lab DEAR 205 • To run, type: sudo wireshark then enter your eecs psswd • Allows you to sniff and analyze traffic sent/received from/by your end system: real measurement of Internet traffic Chapter 1, slide:

  9. Our goal: learn basic network terminologies more depth, detail later in course approach: use Internet as example Chapter 1: Introduction Chapter 1, slide: Acknowledgement: slides drawn heavily from Kurose & Ross

  10. Chapter 1: roadmap 1 What is the Internet? 2 Network edge 3 Network core 4 Internet structure and ISPs 5 Protocol layers, service models 6 Delay & loss in packet-switched networks Chapter 1, slide:

  11. communication infrastructure enables distributed apps: Enables apps to communicate Web, email, games, e-commerce, file sharing communication services provided to apps: Offers services What’s the Internet: a “service” view Chapter 1, slide:

  12. millions of connected computing devices: called hosts or end systems e.g., Laptops, workstations running network apps routers & switches: forward packets (chunks of data) communication links e.g., fiber, copper, radio, satellite router workstation server mobile local ISP regional ISP company network What’s the Internet: “nuts and bolts” view Chapter 1, slide:

  13. Internet standards IETF (Internet Eng. Task Force) RFC: Request for comments IEEE: for links/hardware E.g., Ethernet network protocols control sending/receiving of messages e.g., TCP, IP, HTTP, FTP, PPP What’s the Internet: “nuts and bolts” view router workstation server mobile local ISP regional ISP company network Chapter 1, slide:

  14. a human protocol and a computer network protocol: TCP connection response Get http://www.awl.com/kurose-ross Got the time? 2:00 <file> time What’s a protocol? Hi TCP connection request Hi Chapter 1, slide:

  15. human protocols: “what’s the time?” “I have a question” introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols What’s a protocol? protocols define (1) format, order of msgs sent and received among network entities, and (2) actions taken on msg transmission, receipt Chapter 1, slide:

  16. Chapter 1: roadmap 1 What is the Internet? 2 Network edge 3 Network core 4 Internet structure and ISPs 5 Protocol layers, service models 6 Delay & loss in packet-switched networks Chapter 1, slide:

  17. network edge: applications and hosts network core: routers network of networks access networks, physical media: communication links A closer look at network structure: Chapter 1, slide:

  18. end systems (hosts): run application programs e.g. Web, email at “edge of network” client/server model client host requests, receives service from always-on server e.g. Web browser/server; email client/server peer-to-peer model: minimal (or no) use of dedicated servers e.g. Skype, BitTorrent, KaZaA The network edge: service models Chapter 1, slide:

  19. Chapter 1: roadmap 1 What is the Internet? 2 Network edge 3 Network core 4 Network access and physical media 5 Internet structure and ISPs 6 Protocol layers, service models 7 Delay & loss in packet-switched networks Chapter 1, slide:

  20. mesh of interconnected routers the fundamental question: how is data transferred through net? circuit switching: dedicated circuit per call: telephone net packet-switching: data sent thru net in discrete “chunks” The Network Core Chapter 1, slide:

  21. End-end resources reserved for “call” dedicated resources: no sharing call setup required circuit-like (guaranteed) performance same path for all chunks Network Core: Circuit Switching Chapter 1, slide:

  22. Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces” • allocated pieces per call • no sharing • resource piece idle if not used by owning call Chapter 1, slide:

  23. Network Core: Circuit Switching • Two ways of dividing bandwidth into “pieces” • frequency division • time division Chapter 1, slide:

  24. Example: 4 users Freq. Division Multiplx. (FDM) frequency time Time Division Multiplx. (TDM) frequency time Circuit Switching: FDM and TDM Chapter 1, slide:

  25. each end-to-end data stream is divided into packets no dedication/reservation: all streams share resources no setup is required resources used as needed each packet uses full link bandwidth aggregate resource demand can exceed capacity no guarantee Network Core: Packet Switching 100 Mb/s Ethernet C A 1.5 Mb/s B Chapter 1, slide:

  26. Sequence of A & B packets does not have fixed pattern, shared on demand  statistical multiplexing. Whereas in TDM, each host gets same slot (periodically) D E Network Core: statistical multiplexing 100 Mb/s Ethernet C A statistical multiplexing 1.5 Mb/s B queue of packets waiting for output link Chapter 1, slide:

  27. statistical multiplex. • B uses full link since • A is not using it A Packet switching 2 Mb/s B Packet switching versus circuit switching A Circuit switching • 2 circuits (use TDM) • A reserves 1 circuit • B reserves 1 circuit 2 Mb/s B Utilization = 50% only = 1 Mb/s B: has no packets to send Utilization = 100% = 2 Mb/s Chapter 1, slide:

  28. Packet-switching Circuit-switching Resources sharing dedicated Congestion may lead to it admission control Overhead less overhead; more overhead; no connection setup reserve resources 1st Guarantee Best-effort provide guarantee no guarantee good for multimedia Packet switching versus circuit switching Chapter 1, slide:

  29. Numerical example • How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network? • The link’s transmission rate = 0.64 Mbps • Each link uses TDM with 10 slots/sec • 0.5 sec to establish end-to-end circuit Let’s work it out! You have few minutes! • Solution: • Bandwidth of circuit (in kbps)= .64x1000/10 = 64 kbps • Time to send: 640 kbits/64 kbps + 0.5s = 10.5s Chapter 1, slide:

  30. Announcements: Please make sure to check the course’s website in a regular basis http://web.engr.oregonstate.edu/~qassim/index_files/ComputerNetworks.htm Lab 1 is due on Tuesday ALL HW and LAB ASSIGNMENTS SHOULD BE HARD COPY, SOFT COPY IS NOT ACCEPTED ECE/CS 372 – introduction to computer networksLecture 2 Chapter 1, slide: Acknowledgement: slides drawn heavily from Kurose & Ross

  31. Announcements • Lab • Location: Dearborn 205 • Access code: will be written on board Approach: how to do well in this course • Easy: attend ALL lectures and do ALL assignments • Do your assignments individually • Some hw problems will be solved in class: this gives you the opportunity to clarify things further Chapter 1, slide:

  32. Packet-switching Circuit-switching Resources sharing dedicated Congestion may lead to it admission control Overhead less overhead; more overhead; no connection setup reserve resources 1st Guarantee Best-effort provide guarantee no guarantee good for multimedia Packet switching versus circuit switching Chapter 1, slide:

  33. 3 Mb/s link each user: 1 Mb/s when “active” active 1/3 of time circuit-switching: 3 users packet switching: With N=4 users, what are the chances that a user won’t get 1 Mb/s? I.e., what is the prob. that more than 3 (strictly) users are active? With N=5 users, what are the chances that a user won’t get 1 Mb/s? With N=6 users, what are the chances that a user won’t get 1 Mb/s? Packet switching allows more users to use network! Packet switching versus circuit switching N users 3 Mbps link Chapter 1, slide:

  34. Board … Packet switching versus circuit switching Chapter 1, slide:

  35. Announcements: HW1 is posted and is due Monday of the 3rd week in class. Hard copy only, late HW are not accepted. Announcement section is added to the website ECE/CS 372 – introduction to computer networksLecture 3 Chapter 1, slide: Acknowledgement: slides drawn heavily from Kurose & Ross

  36. Chapter 1: roadmap 1 What is the Internet? 2 Network edge 3 Network core 4 Internet structure and ISPs 5 Protocol layers, service models 6 Delay & loss in packet-switched networks Chapter 1, slide:

  37. roughly hierarchical: tier 1, tier 2, and tier 3 at center: “tier-1” ISPs e.g., MCI, Sprint, AT&T, Cable and Wireless, national/international coverage NAP Tier-1 providers also interconnect at public network access points (NAPs) Tier-1 providers interconnect (peer) privately Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP Chapter 1, slide:

  38. Seattle DS3 (45 Mbps) OC3 (155 Mbps) OC12 (622 Mbps) OC48 (2.4 Gbps) Tacoma New York Stockton Cheyenne Chicago Pennsauken Relay Wash. DC San Jose Roachdale Kansas City Anaheim Atlanta Fort Worth Orlando Tier-1 ISP: e.g., Sprint Sprint US backbone network Chapter 1, slide:

  39. “Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs NAP Tier-2 ISPs also peer privately with each other, interconnect at NAP Tier-2 ISP is customer of tier-1 provider Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP Chapter 1, slide:

  40. “Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems) Tier 3 ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP NAP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP Chapter 1, slide:

  41. a packet passes through many networks! Tier 3 ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP NAP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP Chapter 1, slide:

  42. Chapter 1: roadmap 1 What is the Internet? 2 Network edge 3 Network core 4 Internet structure and ISPs 5 Protocol layers, service models 6 Delay & loss in packet-switched networks Chapter 1, slide:

  43. Networks are complex! many “pieces”: hosts routers links of various media applications protocols hardware, software Question: Is there any hope of an organizing structure of network? Protocol “Layers” Chapter 1, slide:

  44. ticket (complain) baggage (claim) gates (unload) runway landing airplane routing ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing airplane routing Organization of air travel • a series of steps Chapter 1, slide:

  45. ticket ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing baggage gate airplane routing airplane routing takeoff/landing airplane routing departure airport intermediate air-traffic control centers arrival airport Layering of airline functionality Layers: each layer implements a service • via its own internal-layer actions • relying on services provided by layer below Chapter 1, slide:

  46. Why layering? Dealing with complex systems: • Easing assignment of tasks • identify relationship among pieces of complex systems • Easing maintenance, updating of system • change of implementation of layer’s service transparent to rest of system • e.g., change in gate procedure doesn’t affect rest of system Chapter 1, slide:

  47. application: supporting network applications FTP, SMTP, HTTP transport: process-process data transfer TCP, UDP network: routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring network elements PPP, Ethernet physical: bits “on the wire” application transport network link physical Internet protocol stack Chapter 1, slide:

  48. network link physical link physical M M M Ht M Hn Hn Hn Hn Ht Ht Ht Ht M M M M Ht Ht Hn Hl Hl Hl Hn Hn Hn Ht Ht Ht M M M source Encapsulation message application transport network link physical segment datagram frame switch destination application transport network link physical router Chapter 1, slide:

  49. application transport network link physical ISO/OSI Model: late 70’s application presentation session transport network data link physical 5-layer Internet Protocol Stack 7-layer ISO/OSI model (OSI: open system interconnections) Chapter 1, slide:

  50. Chapter 1: roadmap 1 What is the Internet? 2 Network edge 3 Network core 4 Internet structure and ISPs 5 Protocol layers, service models 6 Delay & loss in packet-switched networks Chapter 1, slide:

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