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CNT 4007C Computer Networks Fundamentals

CNT 4007C Computer Networks Fundamentals

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CNT 4007C Computer Networks Fundamentals

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  1. CNT4007CComputer Networks Fundamentals Ahmed Helmy(www.cise.ufl.edu/~helmy) Computer & Information Science & Engineering (CISE) Dept University of Florida Fall 2011 Introduction

  2. Course Outline • 4 homeworks& 2 prog. assign. + 2 major exams • 1 mid-term covering the first half of semester • The Internet (Overview), Layering, Multiplexing, Applications, Transport, Congestion Control, MAC protocols (partial !) [depending on lecture progress] • 2nd exam (final or 2nd mid-term) covering 2nd half • MAC protocols (partial), Wireless Networking and Mobility, Routing (unicast, multicast), Security (partial!) [depending on progress] • 1 required text book (Kurose, Ross… 5th Edition) • Lecture slides: modified version of book slides Introduction

  3. (Open) Questions to think about: • Throughout the semester we can ask the following questions about the services and the design of the Internet: • What do you like about the Internet? • What do you not like about the Internet and would want to change? • How would you change it and how would you achieve such change? Introduction

  4. Intro & Motivation • What’s the Internet to you? • Web browsers, wireless Internet Cafés, cellular phones!, home networks, networked cars, networked embedded devices, inter-planetary networks?… • Complex, time-varying, hard to capture & represent! • Why study the Internet? • To learn engineering lessons from history • Analyze today’s problems and improve performance • Provide future designs for better Internet and apps • Is the Internet the only form of computer networking? Introduction

  5. Topics (Chapters) to Cover • From main text book (Kurose, Ross) • Ch1: Overview, Intro • Ch2: Applications • Ch3: Transport Layer • Ch4: Network Layer • Ch5: Link Layer, MAC, LANs • Ch6: Wireless, Mobile Networks • Ch7: Multimedia [partial?: Diffserv, Intserv] • Ch8: Security [partial]? • Notes: • Ordering maybe slightly modified as semester progresses. • Personal notes, additions will be provided by Prof. as needed. • This is not a programming class (although we will use some prog.). It is not a security class, although we’ll introduce security issues and discuss briefly! Introduction

  6. Chapter 1Introduction Computer Networking: A Top Down Approach ,4th edition. Jim Kurose, Keith RossAddison-Wesley, July 2007. (Updated Apr 09, Sept 10). Introduction

  7. Overview: what’s the Internet? what’s a protocol? network edge; hosts, access net, physical media network core: Internet structure protocol layers, service models network core: packet/circuit switching, performance: loss, delay, throughput security history Chapter 1: Introduction Introduction

  8. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge • end systems, access networks, links 1.3 Network core • circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction

  9. millions of connected computing devices: hosts = end systems run network apps PC Mobile network server Global ISP wireless laptop cellular handheld Home network Regional ISP access points wired links Institutional network router What’s the Internet: “nuts and bolts” view • communication links • fiber, copper, radio, satellite • transmission rate (bandwidth) • routers: • forward packets (chunks of data) Introduction

  10. protocolscontrol sending, receiving of msgs TCP, IP, HTTP, Ethernet Internet: “network of networks” loosely hierarchical public Internet versus private intranet Internet standards RFC: Request for comments IETF: Internet Engineering Task Force Mobile network Global ISP Home network Regional ISP Institutional network What’s the Internet: “nuts and bolts” view Introduction

  11. communication infrastructure enables distributed applications: Web, VoIP, email, games, e-commerce, file sharing communication services provided to apps: reliable data delivery from source to destination “best effort” (unreliable) data delivery What’s the Internet: a service view Introduction

  12. Network protocols: All communication in Internet governed by protocols Generic protocol: specific messages sent specific actions taken when messages are received, or other events (e.g., timer expiration, exception detection) Protocol Representation: Finite State Machines Protocol Specification, via Standards protocols define format, order of messages sent and received among network entities, and actions taken on message transmission, receipt What’s a protocol? Introduction

  13. Example sequence of a computer network protocol: TCP connection response Get http://www.ufl.edu <file> time What’s a protocol? host server TCP connection request Protocol Design and Analysis are extremely important in Internet study, development and research Introduction

  14. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge • end systems, access networks, links 1.3 Network core • circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction

  15. Network edge: applications and hosts A closer look at network structure: • Access networks, physical media: wired, wireless communication links • Network core: • interconnected routers • network of networks Introduction

  16. end systems (hosts): run application programs e.g. Web, email at “edge of network” peer-peer client/server The network edge: • 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, BitTorrenth Introduction

  17. Goal: data transfer between end systems handshaking: setup (prepare for) data transfer ahead of time Hello, initial establishment set up “state” in two communicating hosts TCP - Transmission Control Protocol Internet’s reliable data transfer 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: reliable data transfer service Introduction

  18. Goal: data transfer between end systems same as before! UDP - User Datagram Protocol [RFC 768]: connectionless 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: best effort (unreliable) data transfer service Introduction

  19. Q: How to connect 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 Introduction

  20. 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 • DSL: digital subscriber line • deployment: telephone company (typically) • up to 1 Mbps upstream (today typically < 256 kbps) • up to 8 Mbps downstream (today typically < 1 Mbps) • dedicated physical line to telephone central office Introduction

  21. uses cable TV infrastructure, rather than telephone infrastructure HFC: hybrid fiber coax asymmetric: up to 30Mbps downstream, 2 Mbps upstream network of cable and fiber attaches homes to ISP router homes share access to router unlike DSL, which has dedicated access Residential access: cable modems Introduction

  22. Residential access: cable modems Introduction

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

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

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

  26. 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 (frequency division multiplexing) [more shortly] cable headend home cable distribution network Introduction

  27. Ethernet Internet access • typically used in companies, universities, etc • 10 Mbps, 100Mbps, 1Gbps, 10Gbps Ethernet • today, end systems typically connect into Ethernet switch institutional router 100 Mbps to institution’sISP Ethernet switch 100 Mbps 1 Gbps 100 Mbps server Introduction 1-27

  28. shared wireless access network connects end system to router via base station aka “access point” wireless LANs: 802.11b/g/n (WiFi): 11, 54, 111 Mbps wider-area wireless access provided by telco operator ~1Mbps over cellular (EVDO, HSDPA) WiMAX, LTE (10’sMbps) over wide area? Wireless Networks: Chapter 6 Future: Mobile Ad Hoc and Sensor Networks! router base station mobile hosts Wireless access networks Introduction

  29. Typical home network components: DSL 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 Introduction

  30. 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: 100Mbps Ethernet Physical Media Introduction

  31. Coaxial cable: two concentric copper conductors bidirectional baseband: single channel on cable legacy Ethernet broadband: multiple channels on cable HFC (hybrid fiber-coax) 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 (100’s Gps) • WDM Networks: Wavelength division multiplexing • low error rate: repeaters spaced far apart ; immune to electromagnetic noise Introduction

  32. signal carried in electromagnetic spectrum no physical “wire”, … bidirectional propagation environment effects: reflection obstruction by objects Interference dynamic link characteristics … Physical media: radio Radio link types: • terrestrial microwave • e.g. up to 45 Mbps channels • LAN (e.g., Wifi) • 11Mbps, 54 Mbps • wide-area (e.g., cellular) • 3G cellular: ~ 1 Mbps • satellite • Kbps to 45Mbps channel (or multiple smaller channels) • 270 msec end-end delay • geosynchronous versus low altitude Introduction

  33. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge • end systems, access networks, links 1.3 Network core • network structure, circuit switching, packet switching 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction

  34. Internet Structure: loose hierarchy • hierarchy based on administrative regions/providers Introduction

  35. Internet Hierarchy • hierarchy based on routing (more later) Introduction

  36. roughly hierarchical at center: small # of well-connected large networks “tier-1” commercial ISPs (e.g., Verizon, Sprint, AT&T, Qwest, Level3), national & international coverage large content distributors (Google, Akamai, Microsoft) treat each other as equals (no charges) Large Content Distributor (e.g., Google) Large Content Distributor (e.g., Akamai) IXP IXP Internet structure: network of networks Tier 1 ISP Tier-1 ISPs & Content Distributors, interconnect (peer) privately Tier 1 ISP Tier 1 ISP … or at Internet Exchange Points IXPs Introduction 1-36

  37. POP: point-of-presence to/from backbone peering … …. … … … to/from customers Tier-1 ISP: e.g., Sprint Introduction 1-37

  38. Internet structure: network of networks Large Content Distributor (e.g., Google) Large Content Distributor (e.g., Akamai) Tier 1 ISP Tier 1 ISP Tier 1 ISP IXP IXP “tier-2” ISPs: smaller (often regional) ISPs • connect to one or more tier-1 (provider) ISPs • each tier-1 has many tier-2 customer nets • tier 2 pays tier 1 provider • tier-2 nets sometimes peer directly with each other (bypassing tier 1) , or at IXP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Introduction 1-38

  39. Internet structure: network of networks Large Content Distributor (e.g., Google) Large Content Distributor (e.g., Akamai) Tier 1 ISP Tier 1 ISP Tier 1 ISP IXP IXP • “Tier-3” ISPs, local ISPs • customer of tier 1 or tier 2 network • last hop (“access”) network (closest to end systems) Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Introduction 1-39

  40. Internet structure: network of networks Large Content Distributor (e.g., Google) Large Content Distributor (e.g., Akamai) Tier 1 ISP Tier 1 ISP Tier 1 ISP IXP IXP • a packet passes through many networks from source host to destination host Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Introduction 1-40

  41. a packet passes through many networks down and up the hierarchy! Tier 3 ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP local ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP Introduction

  42. So, what does the Internet look like? Have you seen it lately?! 100 node transit-stub topology Introduction

  43. Map of the multicast backbone [Mbone] (~3000 nodes) [2002] Introduction

  44. Map of the Internet (~50,000 nodes) Introduction

  45. It is not simple… • It is really complex • in scale • in interactions and dynamics • in failure modes (loss, crashes, loops, etc) • We need a very systematic approach to design protocols for such a complex network Introduction

  46. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge • end systems, access networks, links 1.3 Network core • circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction

  47. Networks are complex! many “pieces”: hosts routers links of various media applications protocols hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks? Protocol “Layers” Introduction

  48. Why layering? Dealing with complex systems: • explicit structure allows identification, relationship of complex system’s pieces • layered reference model for discussion • modularization eases maintenance, updating of system • change of implementation of layer’s service transparent to rest of system • change in one layer doesn’t affect rest of system (is this true?!) • Can layering be considered harmful? Introduction

  49. application: supporting network applications FTP, SMTP, HTTP transport: process-process data transfer TCP, UDP network: routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring network elements PPP, Ethernet physical: bits “on the wire” application transport network link physical Internet protocol stack Introduction

  50. presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions session: synchronization, checkpointing, recovery of data exchange Internet stack “missing” these layers! these services, if needed, must be implemented in application needed? application presentation session transport network link physical ISO/OSI reference model Introduction