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Chapter 1: Introduction

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  1. Our goal: get “feel” and terminology more depth, detail later in course approach: 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 network modeling Chapter 1: Introduction Introduction

  2. 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

  3. millions of connected computing devices: hosts = end systems running network apps PC Mobile network server Global ISP wireless laptop smartphone Home network Regional ISP wireless links 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

  4. “Cool” internet appliances Tweet-a-watt: monitor energy use Internet gaming, chatting Computer in refrigerator IP picture frame Radio Frequency Identification (RFID) Internet phones Google map on smartphone Introduction

  5. protocolscontrol sending, receiving of msgs e.g., TCP, IP, HTTP, Skype, 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

  6. 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 Provide a comment playground for everyone What’s the Internet: a service view Introduction

  7. 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 What’s a protocol? protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt Introduction

  8. a human protocol and a computer network protocol: TCP connection response Get Got the time? 2:00 <file> time What’s a protocol? Hi TCP connection request Hi Introduction

  9. 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

  10. 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

  11. 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-peer model: • minimal (or no) use of dedicated servers • e.g. Skype, BitTorrent, Joost Introduction

  12. 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 (TCP) Introduction

  13. 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 No need to setup App’s using TCP: HTTP (Web), FTP (file transfer), Telnet/ssh (remote login), SMTP (email) App’s using UDP: streaming media, teleconferencing, DNS, Internet telephony Network edge: connectionless service (UDP) Introduction

  14. 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

  15. 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 • < 2.5 Mbps upstream transmission rate (typically < 1 Mbps) • < 24 Mbps downstream transmission rate (typically < 10 Mbps) • Why asymmetric ? Why not 0 bps for upstream? Introduction

  16. Access net: digital subscriber line (DSL) ISP voice, data transmitted at different frequencies over dedicated line to central office DSL access multiplexer central office telephone network DSL modem splitter DSLAM • use existing telephone line to central office DSLAM • data over DSL phone line goes to Internet • voice over DSL phone line goes to telephone net • Different ages of phone lines may have different capacities • Your house may not have the new lines that support the top speed in ads Introduction

  17. 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 Access net: cable network cable headend … cable modem splitter frequency division multiplexing: different channels transmitted in different frequency bands Introduction

  18. cable modem termination system data, TV transmitted at different frequencies over shared cable distribution network ISP Access net: cable network cable headend … cable modem splitter CMTS • HFC: hybrid fiber coax • asymmetric: up to 30Mbps downstream transmission rate, 2 Mbps upstream transmission rate • network of cable, fiber attaches homes to ISP router • homes share access networkto cable headend • unlike DSL, which has dedicated access to central office Introduction

  19. often combined in single box cable or DSL modem router, firewall, NAT wireless access point (54 Mbps) wired Ethernet (100 Mbps) Access net: home network wireless devices to/from headend or central office Introduction

  20. Enterprise access networks (Ethernet) institutional link to ISP (Internet) institutional router Ethernet switch institutional mail, web servers • typically used in companies, universities, etc • 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates • today, end systems typically connect into Ethernet switch Introduction

  21. Wireless access networks shared wireless access network connects to router via base station aka “access point” wide-area wireless access • provided by telco (cellular) operator, 10’s km • between 1 and 10 Mbps • 3G, 4G: LTE • WiMAX (31mile, 70Mbps) over wide area? • 802.11 mesh network? wireless LANs: • within building (100 ft) • 802.11b/g (WiFi): 11, 54 Mbps transmission rate to Internet to Internet Introduction

  22. 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 5: 100 Mbps, 1 Gpbs Ethernet Category 6: 10Gbps Why twisted? Physical Media Introduction

  23. Coaxial cable: two concentric copper conductors bidirectional baseband: single channel on cable legacy Ethernet broadband: multiple channels on cable HFC Physical Media: coax, fiber Fiber optic cable: • glass fiber carrying light pulses, each pulse a bit • high-speed operation: • 10’s-100’s Gps • low error rate: immune to electromagnetic noise • Why lights not go out? Introduction

  24. From Google Image: Optical Fiber Cable Introduction

  25. 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., Wifi) • 11Mbps, 54 Mbps • wide-area (e.g., cellular) • 3G cellular: ~ 1 Mbps • 4G (LTE): ~ 1 Gbps (??) • satellite • Kbps to 45Mbps channel (or multiple smaller channels) • 280 msec end-end delay • geosynchronous versus low altitude Introduction

  26. From Google Image: Cellular Tower Microwave dishes Cell tower Introduction

  27. Wireless Sensor Network Sensor nodes monitor nearby environment and send back sensed information Battlefield sensor network Wild life sensor Sensor Mote Introduction

  28. Wireless Ad Hoc Network • Decentralized network • No fixed network infrastructure, routers • Mostly nodes are mobile Unmanned mini helicopter with wireless relay node Emergency ad hoc network Introduction

  29. Harvard School’s New Project: Kilobot (mimic a swarm of fish) Introduction