Welcome to CS 340 Introduction to Computer Networking

Welcome to CS 340 Introduction to Computer Networking

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

Course Overview • Top-down Intro Networking Class – Application down to physical layer • 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

Logistics • Instructor Aleksandar Kuzmanovic (akuzma@cs.northwestern.edu), Office Hours: Th. 2-4pm or by appointment, Rm 356, 1890 Maple Ave. • TA: Bin Lin (binlin@cs.northwestern.edu) Office Hours: Tu. and Th. 11am - noon(12pm), Rm 240, Maple Ave. • TA backup (first 2 weeks): Yi Qiao (yqiao@cs...) Suite 300, Maple Ave.

Prerequisites • A LOT OF WORK – Heavy Projects - but it’s worth! – 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++ – BUILDING software is 50% of the grade of this class

Course Materials • Computer Networking: A Top-Down Approach Featuring the Internet, Third Edition, James Kurose and Keith Ross, Addison Wesley, 2005 • TCP/IP Illustrated, Volume I: The Protocols, Richard Stevens, Addison Wesley, 1994 • See course webpage and syllabus for other recommended books and references

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

Communication • Web page: http://www.cs.nwu.edu/~akuzma/classes/cs340- w05/ • Recitation: Wed., 4-5pm, Room 342, 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

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

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

Network Components (Examples) Links Interfaces Switches/routers Ethernet card Large router Fibers Wireless card Coaxial Cable Telephone switch

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

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

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 1000000000 100000000 10000000 1000000 100000 10000 1000 100 10 1 1981 1984 1987 1990 1993 1996 1999 2002 Data available at: http://www.isc.org/

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

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

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

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

Network Edge: Connectionless Service Goal: data transfer between end systems App’s using TCP: • HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email) – 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 UDP: • streaming media, teleconferencing, DNS, Internet telephony

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

Broadcast vs. Switched Communication Networks • 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

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

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

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

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 Networks) • No dedicated allocation or resource reservation

Packet Switching: Statistical Multiplexing 10 Mbs Ethernet C A statistical multiplexing 1.5 Mbs B queue of packets waiting for output link 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.

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 N users 1 Mbps link • Circuit-switching: – 10 users • Packet switching: – with 35 users, probability > 10 active less than .0004

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)

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

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

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

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 • Features – Guarantees in-sequence delivery of packets (+) – However, packets from different virtual circuits may be interleaved (+) – Requires per-flow state in the network (-)

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 •

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

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

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

Welcome to CS 340 Introduction to Computer Networking