1. Chapter 1, slide: 1 Summer 2010 CS 372 Introduction to Computer Networks* Monday, June 21, 2010 School of Electrical Engineering and Computer Science Oregon State University Course Overview * Based in part on slides by Bechir Hamdaoui and Paul D. Paulson.

2. Chapter 1, slide: 2  Course website  http://classes.engr.oregonstate.edu/eecs/summer2010/cs372/index.html http://classes.engr.oregonstate.edu/eecs/summer2010/cs372/index.html  Please write down this URL—all course material and information will be provided thru this site  Lectures  M-F 1-1:50, WNGR 287  Instructor  Majid Alkaee Taleghan (alkaee@eecs.oregonstate.edu)  Office hours: MW 2-3 @ 3130 KEC Lecture/Office/Lab Hours

3. Chapter 1, slide: 3  Teaching Assistant  Lab  Location: Dearborn 205  Access code  Hours Lecture/Office/Lab Hours

4. Chapter 1, slide: 4 Prerequisite:  CS 261 or an equivalent data structure course  Programming skills in Java  Basic Linux familiarity Textbook Prerequisite/Textbook  Textbook is Required Computer Networking: A Top-Down Approach Featuring the Internet, 5th Edition, Games F. Kurose, Keith W. Ross

5. Chapter 1, slide: 5 Grading Policy  Assignments: 20%  Each student must hand in one copy  5 assignments: approx. 1 every week  Labs: 15%  Groups of 2 are required; each group must hand in one and only one copy  5 labs: approx. 1 every week  Quizzes: 5%  5 quizzes: approx.1 every week  One midterm exam: 25%  Final exam: 35%

6. Chapter 1, slide: 6 Course Goals r Learn the basics of computer networks: concepts, principles, and architecture r Understand how various network protocols work: the Internet will be our underlying example r Observe and analyze network protocols in actions r Write network programs Goals Methods Lecture “principles & concepts” Measurement “Real networks” Labs Assignments

7. Chapter 1, slide: 7 Topics To Be Covered  Architecture of the Internet: network of networks  Network protocols: HTTP, FTP, IEEE  Congestion and flow control: TCP  Routing algorithms: IP and datagram  Packet-switching and circuit-switching  Data link layers and Ethernet: ARP, CSMA/CD  Medium access control and local area networks

8. Chapter 1, slide: 8 Labs: Objective & Approach Objective  Understand how Internet protocols work  Force network protocols to perform certain actions  Observe and analyze protocols’ behavior Approach  Real measurement of Internet traffic  Sniff and analyze traffic sent/received from/by your end system  Software tool: Wireshark (also known as Ethereal)  already installed in Lab DEAR 205  To run, type: sudo wireshark then enter your eecs psswd

9. Chapter 1, slide: 9 Assignments: Objective & Approach Objective  Practice problems to deepen your understanding of basic networking concepts Approach  You are expected to do your assignments individually  Some problems will be solved in class: this gives you the opportunity to clarify things further

10. Chapter 1, slide: 10 Keep in mind …  My mission is to help you learn and understand the material—please do not hesitate to ask for help  I will be available for you to help you with everything: material/assignments/labs  We’ll start after a 5-mn break  please team up for labs…  find your partner …  sign up sheet …

11. Chapter 1, slide: 11 Chapter 1: Introduction Our goal:  learn basic network terminologies  more depth, detail later in course  approach:  use Internet as example Acknowledgement: slides drawn heavily from Kurose & Ross

12. Chapter 1, slide: 12 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

13. Chapter 1, slide: 13 What’s the Internet: a “service” view  communication infrastructure enables distributed applications:  Web, email, games, e- commerce, file sharing  communication services provided to apps:  Connectionless: unreliable  connection-oriented: reliable

14. Chapter 1, slide: 14 What’s the Internet: “nuts and bolts” view  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 local ISP company network regional ISP router workstation server mobile

15. Chapter 1, slide: 15 What’s the Internet: “nuts and bolts” view  network protocols  control sending/receiving of msgs  e.g., TCP, IP, HTTP, FTP, PPP  Internet standards  IETF: Internet Engineering Task Force RFC: Request for comments  IEEE: for links, e.g., Ethernet local ISP company network regional ISP router workstation server mobile

16. Chapter 1, slide: 16 What’s a protocol? a human protocol and a computer network protocol: Hi Got the time? 2:00 TCP connection request TCP connection response Get http://www.awl.com/kurose-ross time

17. Chapter 1, slide: 17 What’s a protocol? 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 protocols define (1) format, order of msgs sent and received among network entities, and (2) actions taken on msg transmission, receipt

18. Chapter 1, slide: 18 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

19. Chapter 1, slide: 19 A closer look at network structure:  network edge: applications and hosts  network core:  routers  network of networks  access networks, physical media: communication links

20. Chapter 1, slide: 20 The network edge: service models  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

21. Chapter 1, slide: 21 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

22. Chapter 1, slide: 22 The Network Core  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”

23. Chapter 1, slide: 23 Network Core: Circuit Switching End-end resources reserved for “call”  dedicated resources: no sharing  call setup required  circuit-like (guaranteed) performance  same path for all chunks

24. Chapter 1, slide: 24 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

25. Chapter 1, slide: 25 Network Core: Circuit Switching  Two ways of dividing bandwidth into “pieces”  frequency division  time division

26. Chapter 1, slide: 26 Circuit Switching: FDM and TDM Freq. Division Multiplx. (FDM) frequency time Time Division Multiplx. (TDM) frequency time 4 users Example:

27. Chapter 1, slide: 27 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 = 1.536 Mbps  Each link uses TDM with 24 slots/sec  500 msec to establish end-to-end circuit Let’s work it out! You have 5 minutes!  Solution:  Bandwidth of circuit = 1.536/24 = 64 kbps  Time to send: 640000 bits/64 kbps + 0.5s = 10.5s

28. Chapter 1, slide: 28 Network Core: Packet Switching 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 A B C 100 Mb/s Ethernet 1.5 Mb/s

29. Chapter 1, slide: 29 Sequence of A & B packets does not have fixed pattern, shared on demand  statistical multiplexing. Whereas in TDM, each host gets same slot (periodically) A B C 100 Mb/s Ethernet 1.5 Mb/s D E statistical multiplexing queue of packets waiting for output link Network Core: statistical multiplexing

30. Chapter 1, slide: 30 Packet-switching: store-and-forward  Takes L/R seconds to transmit (push out) packet of L bits on to link of R bps  delay = 3L/R (assuming zero propagation delay) more on this later … Example:  L = 10,000,000 bits and R = 1 Mbps  delay = 30 sec R R R L Entire packet must arrive at router before it can be transmitted on next link: store and forward

31. Chapter 1, slide: 31 Packet switching versus circuit switching Packet-switching Circuit-switching  Resources sharing dedicated  Congestion may lead to itadmission control  Overhead less overhead;more overhead; no connection setupreserve resources 1st  Guarantee Best-effort provide guarantee no guarantee good for multimedia

32. Chapter 1, slide: 32 A B 2 Mb/s Circuit switching B: has no packets to send 2 circuits (use TDM) A reserves 1 circuit B reserves 1 circuit A B 2 Mb/s Packet switching statistical multiplex. A uses full link since B is not using it Packet switching versus circuit switching Utilization = 50% only = 1 Mb/s Utilization = 100% = 2 Mb/s

33. Chapter 1, slide: 33 Packet switching versus circuit switching  3 Mb/s link  each user:  1 Mb/s when “active”  active 1/3 of time  circuit-switching:  3 users  packet switching:  with 4 users, prob that more than 3 are active is 0.0123  with 5 users, prob. that more than 3 active is ??? (see board notes) Utilization (average % of bandwidth used) Packet switching allows more users to use network (better utilization)! N users 3 Mbps link More of this in assignment 1