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CSCI 3335: Computer Networks Chapter 1 Introduction

CSCI 3335: Computer Networks Chapter 1 Introduction. Vamsi Paruchuri University of Central Arkansas http://faculty.uca.edu/vparuchuri/3335.htm. Some of the material is adapted from J.F Kurose and K.W. Ross. Story of Send. http://www.google.com/green/storyofsend/desktop /. Our goal:

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CSCI 3335: Computer Networks Chapter 1 Introduction

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  1. CSCI 3335: Computer Networks Chapter 1 Introduction Vamsi Paruchuri University of Central Arkansas http://faculty.uca.edu/vparuchuri/3335.htm Some of the material is adapted from J.F Kurose and K.W. Ross

  2. Story of Send • http://www.google.com/green/storyofsend/desktop/ Introduction

  3. 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; hosts, access net, physical media network core: packet/circuit switching, Internet structure performance: loss, delay, throughput security protocol layers, service models history Chapter 1: Introduction Introduction 1-3

  4. Chapter 1: roadmap 1.1 Why do we need a Network and 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 1-4

  5. Goal of Networking • Enable communication between network applicationson different end-points • End-points? computers, cell phones…. • Application? Web, Peer to Peer, Streaming video, IM • Communication? transfer bits or information across a “network” • Network must understand application needs/demands • What data rate? • Traffic pattern? (bursty or constant bit rate) • Traffic target? (multipoint or single destination, mobile or fixed) • App sensitivity? (to delay, “jitter”, loss) • Difficulty: Network may not know these in the first place! • How does the application “use” the network? • Peer to peer: how to find nearest host • Web: how to modulate sending rate? Coexist with other users/apps?

  6. “Fun” internet appliances Web-enabled toaster + weather forecaster IP picture frame http://www.ceiva.com/ Slingbox: watch, control cable TV remotely Internet refrigerator Internet phones Introduction 1-6

  7. millions of connected computing devices: hosts = end systems running 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 1-7

  8. 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 1-8

  9. communication infrastructure enables distributed applications: Web, VoIP, email, games, e-commerce, file sharing Run on end systems 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 1-9

  10. 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 1-10

  11. a human protocol and a computer network protocol: Get http://www.awl.com/kurose-ross Got the time? 2:00 time What’s a protocol? Hi TCP connection request Hi TCP connection response <file> Q: Other human protocols? Eg., USPS Introduction 1-11

  12. Chapter 1: roadmap 1.1What is the Internet? 1.2 Network edge • end systems, access networks, links 1.3Network 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 1-12

  13. 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 1-13

  14. 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 Introduction 1-14

  15. 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 1-15

  16. Dial-up Modem central office telephone network Internet homedial-up modem ISPmodem (e.g., AOL) home PC • uses existing telephony infrastructure • home directly-connected to central office • up to 56Kbps direct access to router (often less) • can’t surf, phone at same time: not “always on” Introduction 1-16

  17. telephone network Digital Subscriber Line (DSL) Existing phone line:0-4KHz phone; 4-50KHz upstream data; 50KHz-1MHz downstream data Internet home phone DSLAM splitter DSL modem central office home PC • uses existing telephone infrastructure • 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 1-17

  18. uses cable TV infrastructure, rather than telephone infrastructure HFC: hybrid fiber coax asymmetric: up to 30Mbps downstream, 2 Mbps upstream network of cable, fiber attaches homes to ISP router homes share access to router unlike DSL, which has dedicated access Residential access: cable modems Introduction 1-18

  19. Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html Introduction 1-19

  20. Cable Network Architecture: Overview Typically 500 to 5,000 homes cable headend home cable distribution network (simplified) Introduction 1-20

  21. server(s) Cable Network Architecture: Overview cable headend home cable distribution network Introduction 1-21

  22. Cable Network Architecture: Overview cable headend home cable distribution network (simplified) Introduction 1-22

  23. 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 (more shortly): cable headend home cable distribution network Introduction 1-23

  24. ONT ONT ONT Fiber to the Home opticalfibers Internet • optical links from central office to the home • two competing optical technologies: • Passive Optical network (PON) • Active Optical Network (PAN) • much higher Internet rates; fiber also carries television and phone services opticalfiber OLT optical splitter central office Introduction 1-24

  25. 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 1-25

  26. shared wireless access network connects end system to router via base station aka “access point” wireless LANs: 802.11b/g (WiFi): 11 or 54 Mbps wider-area wireless access provided by telco operator ~1Mbps over cellular system (EVDO, HSDPA) next up (?): WiMAX (10’s Mbps) over wide area Wireless access networks router base station mobile hosts Introduction 1-26

  27. 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 1-27

  28. 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 1-28

  29. 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: • high-speed point-to-point transmission (e.g., 10’s-100’s Gpbs) • low error rate: repeaters spaced far apart ; immune to electromagnetic noise Introduction 1-29

  30. 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 • satellite • Kbps to 45Mbps channel (or multiple smaller channels) • 270 msec end-end delay • geosynchronous versus low altitude Introduction 1-30

  31. Chapter 1: roadmap 1.1What 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 1-31

  32. 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 Introduction 1-32

  33. 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 Introduction 1-33

  34. 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 Introduction 1-34

  35. Example: 4 users FDM frequency time TDM frequency time Circuit Switching: FDM and TDM Introduction 1-35

  36. Numerical example • How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network? • all link speeds: 1.536 Mbps • each link uses TDM with 24 slots/sec • 500 msec to establish end-to-end circuit Let’s work it out! Introduction 1-36

  37. 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 • node receives complete packet before forwarding Introduction 1-37

  38. sequence of A & B packets has no fixed timing pattern bandwidth shared on demand: statistical multiplexing. TDM: each host gets same slot in revolving TDM frame. D E Packet Switching: Statistical Multiplexing 100 Mb/s Ethernet C A statisticalmultiplexing 1.5 Mb/s B queue of packets waiting for output link Introduction 1-38

  39. Benefits of Statistical Multiplexing (SM) TDM: Flow gets chance in fixed time-slots SM: Flow gets chance on demand; no need to wait for slot Packets Better Link Utilization

  40. takes L/R seconds to transmit (push out) packet of L bits on to link at R bps store and forward: entire packet must arrive at router before it can be transmitted on next link delay = 3L/R (assuming zero propagation delay) Example: L = 7.5 Mbits R = 1.5 Mbps transmission delay = 15 sec Packet-switching: store-and-forward L R R R more on delay shortly … Introduction 1-40

  41. Example: 1 Mb/s link each user: 100 kb/s when “active” active 10% of time circuit-switching: 10 users packet switching: with 35 users, probability > 10 active at same time is less than .0004 Packet switching allows more users to use network! Q: how did we get value 0.0004? Q: what happens if > 35 users ? Packet switching versus circuit switching N users ….. 1 Mbps link Introduction 1-41

  42. 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 7) Is packet switching a “slam dunk winner?” Packet switching versus circuit switching Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)? Introduction 1-42

  43. 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 1-43

  44. POP: point-of-presence to/from backbone peering … …. … … … to/from customers Tier-1 ISP: e.g., Sprint Introduction 1-44

  45. 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 1-45

  46. 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 1-46

  47. 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 1-47

  48. Chapter 1: roadmap 1.1What 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 1-48

  49. packets queue in router buffers packet arrival rate to link exceeds output link capacity packets queue, wait for turn packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers How do loss and delay occur? A B Introduction 1-49

  50. dproc: nodal processing check bit errors determine output link typically < msec transmission A propagation B nodal processing queueing Four sources of packet delay dnodal = dproc + dqueue + dtrans + dprop dqueue: queueing delay • time waiting at output link for transmission • depends on congestion level of router Introduction 1-50

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