1. Welcome to CS 340 Introduction to Computer Networking

2. Some slides are in courtesy of J. Kurose and K. Ross Overview Course Administrative Trivia Internet Architecture Network Protocols Network Edge A taxonomy of communication networks

3. Top-down Intro Networking Class –Application down to physical layer Small Class –More attention to each student Topics to Cover –Overview of Internet architecture, protocols –Network applications (HTTP, FTP) and programming –Transport (TCP, UDP), congestion/flow control –Network (IP), routing, multicast –Data Link, error handling, LAN, wireless Course Overview

4. Logistics Instructor Yan Chen (ychen@cs.northwestern.edu),ychen@cs.northwestern.edu Office Hours: Th. 2-4pm or by appointment, Rm 330, 1890 Maple Ave. TA Ashish Gupta (ashish@cs.northwestern.edu) Office Hours: Tu. and Th. 11am - noon(12pm), Rm 240, Maple Ave.ashish@cs.northwestern.edu

5. Prerequisites A LOT OF WORK – Heavy Projects –Build a TCP stack and a Web server that runs on it –IP routing Required: CS311 (data structure) Highly Recommended: OS or having some familiarity with Unix systems programming, preferably in C or C++ –Minet is in C++ / STL –BUILDING software is 50% of the grade of this class

6. Course Materials Computer Networking: A Top-Down Approach Featuring the Internet, Second Edition, James Kurose and Keith Ross, Addison Wesley, 2002Computer Networking: A Top-Down Approach Featuring the Internet TCP/IP Illustrated, Volume I: The Protocols, Richard Stevens, Addison Wesley, 1994TCP/IP Illustrated, Volume I: The Protocols See course webpage and syllabus for other recommended books and references

7. Grading Homeworks (4 sets) 10% Projects 50% –Web client/server10% –TCP stack25% –IP routing15% Midterm 20% Final 20% –Exams in-class, closed-book, non-cumulative Late policy: 10% each day after the due date No cheating

8. Communication Web page: http://www.cs.nwu.edu/~ychen/classes/cs340/ http://www.cs.nwu.edu/~ychen/classes/cs340/ Recitation: Wed., 4-5pm, Room 381, 1890 Maple. –TA lectures on the homework and projects, and help to prepare the exams. Newsgroup are available –cs.340.annouce (course announcement) –cs.340.discuss (posting Q & A) Send emails to instructor and TA for questions inappropriate in newsgroup

9. Overview Course administrative trivia Internet Architecture Network Protocols Network Edge A taxonomy of communication networks

10. What’s the Internet: “nuts and bolts” view Millions of connected computing devices: hosts, end-systems –PCs, servers –PDAs, phones, toasters, shoes running network apps Communication links –Fiber, cable, radio, satellite –Residential access: modem, DSL, cable modem, satellite –Transmission rate = bandwidth Routers: forward packets (chunks of data) local ISP company network regional ISP router workstation server mobile

11. Network Components (Examples) Fibers Coaxial Cable LinksInterfacesSwitches/routers Ethernet card Wireless card Large router Telephone switch

12. What’s the Internet: “nuts and bolts” view protocols control sending, receiving of msgs –e.g., TCP, IP, HTTP, FTP Internet: “network of networks” –loosely hierarchical –public Internet versus private intranet communication infrastructure enables distributed applications: –Web, email, games, e- commerce, database., voting, file (MP3) sharing local ISP company network regional ISP router workstation server mobile

13. History of the Internet 70’s: started as a research project, 56 kbps, < 200 computers 80-83: ARPANET and MILNET split 85-86: NSF builds NSFNET as backbone, links 6 Supercomputer centers, 1.5 Mbps, 10,000 computers 87-90: link regional networks, NSI (NASA), ESNet(DOE), DARTnet, TWBNet (DARPA), 100,000 computers 90-92: NSFNET moves to 45 Mbps, 16 mid-level networks 95: NSF backbone dismantled, multiple private backbones Today: backbones run at 10 Gbps, close to 200 millions computers in 150 countries

14. Growth of the Internet Number of Hosts on the Internet: Aug. 1981 213 Oct. 1984 1,024 Dec. 1987 28,174 Oct. 1990 313,000 Oct. 1993 2,056,000 Apr. 1995 5,706,000 Jan. 1997 16,146,000 Jan. 1999 56,218,000 Jan. 2001 109,374,000 Jan 2003 171,638,297 Data available at: http://www.isc.org/

15. Backbone (Teleglobe)

16. Overview Course administrative trivia Internet Architecture Network Protocols Network Edge A taxonomy of communication networks

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 format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

18. What’s a protocol? a human protocol and a computer network protocol: Hi Got the time? 2:00 TCP connection req TCP connection response Get http://www.cs.nwu.edu time

19. Overview Course administrative trivia Internet Architecture Network Protocols Network Edge A taxonomy of communication networks

20. The Network Edge 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. Gnutella, KaZaA

21. Network Edge: Connection-oriented Service Goal: data transfer between end systems handshaking: setup (prepare for) data transfer ahead of time –Hello, hello back human protocol –set up “state” in two communicating hosts TCP - Transmission Control Protocol –Internet’s connection- oriented service TCP service [RFC 793] reliable, in-order byte- stream data transfer –loss: acknowledgements and retransmissions flow control: –sender won’t overwhelm receiver congestion control: –senders “slow down sending rate” when network congested

22. Network Edge: Connectionless Service Goal: data transfer between end systems –same as before! UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service –unreliable data transfer –no flow control –no congestion control App’s using TCP: HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP: streaming media, teleconferencing, DNS, Internet telephony

23. Overview Course administrative trivia Internet Architecture Network Protocols Network Edge A taxonomy of communication networks

24. The fundamental question: how is data transferred through net (including edge & core)? Communication networks can be classified based on how the nodes exchange information: A Taxonomy of Communication Networks Communication Networks Switched Communication Network Broadcast Communication Network Circuit-Switched Communication Network Packet-Switched Communication Network Datagram Network Virtual Circuit Network TDM FDM

25. Broadcast communication networks –Information transmitted by any node is received by every other node in the network Examples: usually in LANs (Ethernet, Wavelan) –Problem: coordinate the access of all nodes to the shared communication medium (Multiple Access Problem) Switched communication networks –Information is transmitted to a sub-set of designated nodes Examples: WANs (Telephony Network, Internet) –Problem: how to forward information to intended node(s) This is done by special nodes (e.g., routers, switches) running routing protocols Broadcast vs. Switched Communication Networks

26. The fundamental question: how is data transferred through net (including edge & core)? Communication networks can be classified based on how the nodes exchange information: A Taxonomy of Communication Networks Communication Networks Switched Communication Network Broadcast Communication Network Circuit-Switched Communication Network Packet-Switched Communication Network Datagram Network Virtual Circuit Network TDM FDM

27. Circuit-Switched Network End-end resources reserved for “call” Link bandwidth, switch capacity Three phases 1.circuit establishment 2.data transfer 3.circuit termination Dedicated resources + Guaranteed performance - no sharing

28. Circuit Switching Examples Telephone networks ISDN (Integrated Services Digital Networks) network resources (e.g., bandwidth) divided into “pieces” Pieces allocated to calls Resource piece idle if not used by owning call (no sharing) Dividing link bandwidth into “pieces” –frequency division –time division

29. Circuit Switching: FDM and TDM FDM frequency time TDM frequency time 4 users Example:

30. The fundamental question: how is data transferred through net (including edge & core)? Communication networks can be classified based on how the nodes exchange information: A Taxonomy of Communication Networks Communication Networks Switched Communication Network Broadcast Communication Network Circuit-Switched Communication Network Packet-Switched Communication Network Datagram Network Virtual Circuit Network TDM FDM

31. Packet Switching Data is sent as formatted bit-sequences (Packets) Packets have the following structure: –Header and Trailer carry control information (e.g., destination address, check sum) Each packet traverses the network from node to node along some path (Routing) At each node the entire packet is received, stored briefly, and then forwarded to the next node (Store-and- Forward Networks) No dedicated allocation or resource reservation HeaderData Trailer

32. Packet Switching: Statistical Multiplexing Sequence of A & B packets does not have fixed pattern  statistical multiplexing. In TDM each host gets same slot in revolving TDM frame. A B C 10 Mbs Ethernet 1.5 Mbs D E statistical multiplexing queue of packets waiting for output link

33. Packet Switching versus Circuit Switching 1 Mbit link Each user: –100 kbps when “active” –active 10% of time Circuit-switching: –10 users Packet switching: –with 35 users, probability > 10 active less than.0004 Packet switching allows more users to use network! N users 1 Mbps link

34. Packet Switching versus Circuit Switching Great for bursty data –resource sharing –simpler, no call setup Excessive congestion: packet delay and loss –protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior? –bandwidth guarantees needed for audio/video apps –still an unsolved problem (chapter 6)

35. The fundamental question: how is data transferred through net (including edge & core)? Communication networks can be classified based on how the nodes exchange information: A Taxonomy of Communication Networks Communication Networks Switched Communication Network Broadcast Communication Network Circuit-Switched Communication Network Packet-Switched Communication Network Datagram Network Virtual Circuit Network TDM FDM

36. Datagram Packet Switching Each packet is independently switched –Each packet header contains destination address which determines next hop –Routes may change during session No resources are pre-allocated (reserved) in advance Example: IP networks

37. Packet 1 Packet 2 Packet 3 Packet 1 Packet 2 Packet 3 Timing of Datagram Packet Switching Packet 1 Packet 2 Packet 3 processing delay of Packet 1 at Node 2 Host 1Host 2 Node 1Node 2 propagation delay between Host 1 and Node 2 transmission time of Packet 1 at Host 1

38. Datagram Packet Switching Host A Host B Host E Host D Host C Node 1 Node 2 Node 3 Node 4 Node 5 Node 6 Node 7

39. The fundamental question: how is data transferred through net (including edge & core)? Communication networks can be classified based on how the nodes exchange information: A Taxonomy of Communication Networks Communication Networks Switched Communication Network Broadcast Communication Network Circuit-Switched Communication Network Packet-Switched Communication Network Datagram Network Virtual Circuit Network TDM FDM

40. Virtual-Circuit Packet Switching Hybrid of circuit switching and packet switching –All packets from one packet stream are sent along a pre-established path (= virtual circuit) –Each packet carries tag (virtual circuit ID), tag determines next hop Guarantees in-sequence delivery of packets However, packets from different virtual circuits may be interleaved Example: ATM (Asynchronous Transfer Mode) networks

41. Virtual-Circuit Packet Switching Communication with virtual circuits takes place in three phases 1.VC establishment 2.data transfer 3.VC disconnect Note: packet headers don’t need to contain the full destination address of the packet

42. Packet 1 Packet 2 Packet 3 Packet 1 Packet 2 Packet 3 Timing of Virtual-Circuit Packet Switching Packet 1 Packet 2 Packet 3 Host 1Host 2 Node 1Node 2 propagation delay between Host 1 and Node 1 VC establishment VC termination Data transfer

43. Virtual-Circuit Packet Switching Host A Host B Host E Host D Host C Node 1 Node 2 Node 3 Node 4 Node 5 Node 6 Node 7

44. Summary Course Administrative Trivia Internet Architecture, Protocols and Taxonomy Eight handouts –Syllabus, Project 1, and its complementary materials Project 1 out –If you don’t have a TLAB account and a keycard to get into the lab, fill the form. –Find partner (groups of 2 preferred) Recitation tomorrow on UNIX programming and project 1