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CSE 5344 Computer Networks

CSE 5344 Computer Networks. Section 002 Hao Che Wolf Hall 308 10:30pm – 11:50am, Monday & Wednesday. Networks I - Computer Network Organization (CSE5344). Instructor: Hao Che ( hche@cse.uta.edu ) GTA: Gang (Gary) Wang and Nirmalya Roy

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CSE 5344 Computer Networks

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  1. CSE 5344 Computer Networks Section 002 Hao Che Wolf Hall 308 10:30pm – 11:50am, Monday & Wednesday

  2. Networks I - Computer Network Organization (CSE5344) • Instructor: Hao Che (hche@cse.uta.edu) • GTA: Gang (Gary) Wang and Nirmalya Roy • Class Web Site: http://crystal.uta.edu/~hche/cse5344/index.html • Required Text: Computer Networking - A Top-Down Approach Featuring the Internet, Kurose-Ross (ISBN 0-201-47711-4) • Course Objective: Have some fun, and learn about how modern networks work, with a focus on the practical applications that most of you see and use every day. Not a study of the OSI model, or older technologies/protocols. Not a certification course for Network Specialists.

  3. Brief Bio • Nanjing University, China: B.S. (1984) in Astrophysics • UT/Arlington: M.S. (1994) in Physics • UT/Austin: Ph.D. (1998) in ECE • Penn State University: Assistant Professor (1998-2000) in EE • Santera Systems Inc: System Architect (2000-2002) • UT/Arlington: Assistant Professor (Now) in CSE

  4. Course Admin • Schedule • Ambitious... may be modified... check web site frequently • Web Site:http://crystal.uta.edu/~hche/cse5344/index.html • Schedule, Syllabus, Class Materials/Information • Email - will be used for time-critical info • Send me an email note from your preferred email account with your full name and “CSE 5344” in the subject line today • Grading Policy (subject to changes) • Homework (5) 20% • Programs/Projects (2) 20% • Exam (2) 30% • Final Paper/Project 10% • Final Exam 20% • Make-Up Policy • Homework, Programs/Projects: 10%/day, max of 40%, then zero • Quizzes and Exams: NO make-ups.

  5. Course Admin • Final Grade Assignment (generally) • Based on final numeric score out of 100% possible: • A 100-90 • B 89- 80 • C 79-70 • D 69-60 • F 59 & below • Attendance… expected • Honesty… expected, dishonesty will not be tolerated • Discussions, brainstorming are encouraged, HOWEVER • Homework, Final Paper & Programming Assignments, Quizzes, Exams, etc. are to be YOUR individual work • See the UTA Handbook of Operating Procedures or the Judicial Affairs website at http://www2.uta.edu/discipline • Cheating • Collusion • Plagiarism

  6. Course Admin • Office Hours • General Rule: If it’s not during scheduled office hours,or if you don’t have an appointment….. I’m not in. • Individual grades or questions on grading of individual quizzes, exams, etc. are discussed only during office hours (i.e. NOT at the end of class period) • Hao Che’s Office Hours (NH 325) • Monday and Wednesday: 1:00pm – 2:30pm • or, by Appointment (i.e. a time scheduled in advance) • GTAs’ Office Hours • Gary (ELAB 201) - Fri, 1:00pm-3:00pm • Nirmalya (WH 412) - Mon & Fri, 11:00am-12:30pm

  7. What really happens when I………? How does my email get from point a to point b? What do all these network “buzzwords” mean to me? Why does my browser respond slowly at times? How does an IP address actually find a web site? request reply application transport network data link physical application transport network data link physical What’s this all about?? 192.168.xxx.xx Router TCP/IP DNS PPP Switch HTTP LAN Edge POP3

  8. Introduction and Networking Overview (Ch. 1) Overview of network components and the Internet The Application Layer (Ch. 2) How you get work done in the network The Transport Layer (Ch. 3) Why your data gets there The Network Layer & Routing (Ch. 4 and other refs) How your data finds its way The Data Link Layer & LANs (Ch. 5) What ties the network pieces together The Physical Layer (will put together a set of slides) How bits are sent through a communication channel VoIP (Part of Ch. 6 and other refs) How voice gets into the IP world Network Security (Part of Ch. 7 and other refs) Access control/Firewall, NAT, and dNAT Network Management (Ch. 8) What tools in the network help keep you “online” Top-Down Application Presentation Session Transport Network Data Link Physical Traditional Learning Approach: Top-Down

  9. Chapter 1 - Computer Networks and the Internet An overview of computer networking which introduces many key concepts and terminology. Sets the stage for future topics.

  10. Our goal: get context, overview, “feel” of networking more depth, detail later in course approach: descriptive use Internet as example Overview: what’s the Internet what’s a protocol? network edge network core access net, physical media Internet/ISP structure performance: loss, delay protocol layers, service models history Chapter 1: Introduction

  11. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History

  12. millions of connected computing devices: hosts, end-systems PCs workstations, servers PDAs, phones, toasters running network apps communication links fiber, copper, radio, satellite transmission rate = bandwidth routers: forward packets (chunks of data) router workstation server mobile local ISP regional ISP company network What’s the Internet: “nuts and bolts” view

  13. “Cool” internet appliances IP picture frame http://www.ceiva.com/ Web-enabled toaster+weather forecaster World’s smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.html

  14. protocolscontrol sending, receiving of msgs e.g., TCP, IP, HTTP, FTP, PPP Internet: “network of networks” loosely hierarchical public Internet versus private intranet Internet standards RFC: Request for comments IETF: Internet Engineering Task Force What’s the Internet: “nuts and bolts” view router workstation server mobile local ISP regional ISP company network

  15. communication infrastructure enables distributed applications: Web, email, games, e-commerce, database., voting, file (MP3) sharing communication services provided to apps: connectionless connection-oriented What’s the Internet: a service view

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

  17. 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 req Hi Q: Other human protocols?

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

  19. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History

  20. 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-peer model: minimal (or no) use of dedicated servers e.g. Gnutella, KaZaA The network edge:

  21. 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 Network edge: connection-oriented service

  22. 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 Network edge: connectionless service

  23. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History

  24. 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

  25. End-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required Network Core: Circuit Switching

  26. network resources (e.g., bandwidth) divided into “pieces” pieces allocated to calls resource piece idle if not used by owning call (no sharing) Network Core: Circuit Switching • dividing link bandwidth into “pieces” • frequency division • time division

  27. Example: 4 users FDMA frequency time TDMA frequency time Circuit Switching: TDMA and TDMA

  28. each end-end data stream divided into packets user A, B packets share network resources each packet uses full link bandwidth resources used as needed Bandwidth division into “pieces” Dedicated allocation Resource reservation Network Core: Packet Switching resource contention: • aggregate resource demand can exceed amount available • congestion: packets queue, wait for link use • store and forward: packets move one hop at a time • transmit over link • wait turn at next link

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

  30. 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! Packet switching versus circuit switching N users 1 Mbps link

  31. 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) Is packet switching a “slam dunk winner?” Packet switching versus circuit switching

  32. Takes L/R seconds to transmit (push out) packet of L bits on to link or R bps Entire packet must arrive at router before it can be transmitted on next link: store and forward delay = 3L/R Example: L = 7.5 Mbits R = 1.5 Mbps delay = 15 sec Packet-switching: store-and-forward L R R R

  33. Now break up the message into 5000 packets Packet Switching: Message Segmenting • Each packet 1,500 bits • 1 msec to transmit packet on one link • pipelining: each link works in parallel • Delay reduced from 15 sec to 5.002 sec

  34. Goal: move packets through routers from source to destination we’ll study several path selection (i.e. routing)algorithms (chapter 4) datagram network: destination address in packet determines next hop routes may change during session analogy: driving, asking directions virtual circuit network: each packet carries tag (virtual circuit ID), tag determines next hop fixed path determined at call setup time, remains fixed thru call routers maintainper-call state Packet-switched networks: forwarding

  35. Packet-switched networks Circuit-switched networks FDM TDM Datagram Networks Networks with VCs Network Taxonomy Telecommunication networks • Datagram network is not either connection-oriented • or connectionless. • Internet provides both connection-oriented (TCP) and • connectionless services (UDP) to apps.

  36. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History

  37. Q: How to connection end systems to edge router? residential access nets institutional access networks (school, company) mobile access networks Keep in mind: bandwidth (bits per second) of access network? shared or dedicated? Access networks and physical media

  38. Dialup via modem up to 56Kbps direct access to router (often less) Can’t surf and phone at same time: can’t be “always on” Residential access: point to point access • ADSL: asymmetric digital subscriber line • up to 1 Mbps upstream (today typically < 256 kbps) • up to 8 Mbps downstream (today typically < 1 Mbps) • FDM: 50 kHz - 1 MHz for downstream 4 kHz - 50 kHz for upstream 0 kHz - 4 kHz for ordinary telephone

  39. HFC: hybrid fiber coax asymmetric: up to 10Mbps upstream, 1 Mbps downstream network of cable and fiber attaches homes to ISP router shared access to router among home issues: congestion, dimensioning deployment: available via cable companies, e.g., MediaOne Residential access: cable modems

  40. Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

  41. Cable Network Architecture: Overview Typically 500 to 5,000 homes cable headend home cable distribution network (simplified)

  42. Cable Network Architecture: Overview cable headend home cable distribution network (simplified)

  43. server(s) Cable Network Architecture: Overview cable headend home cable distribution network

  44. C O N T R O L D A T A D A T A V I D E O V I D E O V I D E O V I D E O V I D E O V I D E O 5 6 7 8 9 1 2 3 4 Channels Cable Network Architecture: Overview FDM: cable headend home cable distribution network

  45. company/univ local area network (LAN) connects end system to edge router Ethernet: shared or dedicated link connects end system and router 10 Mbs, 100Mbps, Gigabit Ethernet deployment: institutions, home LANs happening now LANs: chapter 5 Company access: local area networks

  46. shared wireless access network connects end system to router via base station aka “access point” wireless LANs: 802.11b (WiFi): 11 Mbps wider-area wireless access provided by telco operator 3G ~ 384 kbps Will it happen?? WAP/GPRS in Europe router base station mobile hosts Wireless access networks

  47. Typical home network components: ADSL or cable modem router/firewall/NAT Ethernet wireless access point Home networks wireless laptops to/from cable headend cable modem router/ firewall wireless access point Ethernet (switched)

  48. Bit: propagates betweentransmitter/rcvr pairs physical link: what lies between transmitter & receiver guided media: signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely, e.g., radio Twisted Pair (TP) two insulated copper wires Category 3: traditional phone wires, 10 Mbps Ethernet Category 5 TP: 100Mbps Ethernet Physical Media

  49. Coaxial cable: two concentric copper conductors bidirectional baseband: single channel on cable legacy Ethernet broadband: multiple channel on cable HFC Physical Media: coax, fiber Fiber optic cable: • glass fiber carrying light pulses, each pulse a bit • high-speed operation: • high-speed point-to-point transmission (e.g., 5 Gps) • low error rate: repeaters spaced far apart ; immune to electromagnetic noise

  50. signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: reflection obstruction by objects interference Physical media: radio Radio link types: • terrestrial microwave • e.g. up to 45 Mbps channels • LAN (e.g., WaveLAN) • 2Mbps, 11Mbps • wide-area (e.g., cellular) • e.g. 3G: hundreds of kbps • satellite • up to 50Mbps channel (or multiple smaller channels) • 270 msec end-end delay • geosynchronous versus LEOS

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