Welcome to CS 340 Introduction to Computer Networking

Transcription

1 Welcome to CS 340 Introduction to Computer ing

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

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

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

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

7 Grading Homeworks (4 sets) 10% Projects 50% Web client/server 10% TCP stack 25% IP routing 15% Midterm 20% Final 20% Exams in-class, closed-book, non-cumulative Late policy: 10% each day after the due date No cheating

8 Web page: 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 s to instructor and TA for questions inappropriate in newsgroup

9 Overview Course administrative trivia Internet Architecture Protocols 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 router server local ISP workstation mobile links regional ISP Fiber, cable, radio, satellite Residential access: modem, DSL, cable modem, satellite Transmission rate = bandwidth Routers: forward packets (chunks of data) company network

11 Components (Examples) Links Interfaces Switches/routers Fibers Ethernet card Large router Wireless card Coaxial Cable 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, , games, e- commerce, database., voting, file (MP3) sharing router local ISP company network server workstation mobile regional ISP

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 Oct ,024 Dec ,174 Oct ,000 Oct ,056,000 Apr ,706,000 Jan ,146,000 Jan ,218,000 Jan ,374,000 Jan ,638, Data available at:

15 Backbone (Teleglobe)

16 Overview Course administrative trivia Internet Architecture Protocols 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 Hi Got the time? 2:00 time TCP connection req TCP connection response Get <file>

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

20 End systems (hosts): The Edge run application programs e.g. Web, at edge of network Client/server model client host requests, receives service from always-on server e.g. Web browser/server; client/server Peer-to-peer model: minimal (or no) use of dedicated servers e.g. Gnutella, KaZaA

21 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 connectionoriented service TCP service [RFC 793] reliable, in-order bytestream data transfer loss: acknowledgements and retransmissions flow control: sender won t overwhelm receiver congestion control: senders slow down sending rate when network congested

22 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 ( ) App s using UDP: streaming media, teleconferencing, DNS, Internet telephony

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

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

25 Broadcast vs. Switched s 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, Internet) Problem: how to forward information to intended node(s) This is done by special nodes (e.g., routers, switches) running routing protocols

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

27 Circuit-Switched 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 Examples Circuit Switching Telephone networks ISDN (Integrated Services Digital s) 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 Example: 4 users frequency TDM time frequency time

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

31 Packet Switching Data is sent as formatted bit-sequences (Packets) Packets have the following structure: Header Data Trailer 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 s) No dedicated allocation or resource reservation

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

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

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

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

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

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

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

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

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