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Fall 2014 COMP 4605/5605 Computer Networks

Chapter 1 Introduction. Fall 2014 COMP 4605/5605 Computer Networks. Donghyun (David) Kim Department of Mathematics and Physics North Carolina Central University. Chapter 1: Introduction. Our goal: get “feel” and terminology more depth, detail later in course approach:

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Fall 2014 COMP 4605/5605 Computer Networks

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  1. Chapter 1Introduction Fall 2014COMP 4605/5605Computer Networks Donghyun (David) Kim Department of Mathematics and PhysicsNorth Carolina Central University Some slides are in courtesy of J. Kurose and K. Ross

  2. Chapter 1: Introduction 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 (skipped) Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  3. 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 Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  4. 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 • communication links • fiber, copper, radio, satellite • transmission rate = bandwidth What’s the Internet: “Nuts and Bolts” View • routers: forward packets (chunks of data)

  5. “Cool” Internet Appliances Web-enabled toaster + weather forecaster IP picture frame http://www.ceiva.com/ World’s smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.html Internet phones Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  6. Mobile network Global ISP Home network Regional ISP Institutional network • protocols control 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 What’s the Internet: “Nuts and Bolts” View

  7. 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

  8. What’s a Protocol? network protocols • machines rather than humans • all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt human protocols “what’s the time?” “I have a question” introductions … specific msgs sent … specific actions taken when msgs received, or other events Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  9. TCP connection response Get http://www.cs.nccu.edu Got the time? 2:00 <file> time What’s a Protocol? Hi TCP connection req Hi A human protocol and a computer network protocol: Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  10. 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 Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  11. network edge: applications and hosts • access networks, physical media: wired, wireless communication links • network core: • interconnected routers • network of networks A Closer Look at Network Structure:

  12. peer-peer client/server • 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 The Network Edge • peer-peer model: • minimal (or no) use of dedicated servers • e.g. Skype, BitTorrent

  13. 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

  14. Dial-up Modem central office telephone network Internet homedial-up modem ISPmodem (e.g., AOL) home PC Uses existing telephony infrastructure Home is connected to central office up to 56Kbps direct access to router (often less) Can’t surf and phone at same time: not “always on” Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  15. 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 Also 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 Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  16. Residential Access: Cable Modems • Does not use telephone infrastructure • Instead uses cable TV 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 Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  17. Residential Access: Cable Modems Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  18. Cable Network Architecture: Overview Typically 500 to 5,000 homes cable headend home cable distribution network (simplified) Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  19. server(s) Cable Network Architecture: Overview Typically 500 to 5,000 homes cable headend home cable distribution network (simplified) Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  20. Cable Network Architecture: Overview cable headend home cable distribution network (simplified) Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  21. 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 (simplified) Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  22. ONT ONT ONT Fiber to the Home opticalfibers Internet opticalfiber OLT optical splitter central office • 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 Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  23. Ethernet Internet Access 100 Mbps Institutional router To Institution’sISP Ethernet switch 100 Mbps 1 Gbps 100 Mbps server Typically used in companies, universities, etc 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet Today, end systems typically connect into Ethernet switch Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  24. Wireless Access Networks router base station mobile hosts • 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 Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  25. Home Networks wireless laptops to/from cable headend cable modem router/ firewall wireless access point Ethernet • Typical home network components: • DSL or cable modem • router/firewall/NAT • Ethernet • wireless access • point Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  26. Physical Media • 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 Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  27. 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 Gps) • low error rate: repeaters spaced far apart ; immune to electromagnetic noise Coaxial cable: • two concentric copper conductors • bidirectional • baseband: • single channel on cable • legacy Ethernet • broadband: • multiple channels on cable • HFC Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  28. 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 • signal carried in electromagnetic spectrum • no physical “wire” • bidirectional • propagation environment effects: • reflection • obstruction by objects • interference Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  29. 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 Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  30. 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

  31. Network Core: Circuit Switching End-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  32. Network Core: Circuit Switching • dividing link bandwidth into “pieces” • frequency division • time division network resources (e.g., bandwidth) divided into “pieces” pieces allocated to calls resource piece idle if not used by owning call (no sharing) Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  33. Example: 4 users FDM frequency time TDM frequency time Circuit Switching: FDM and TDM Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  34. 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 links are 1.536 Mbps • Each link uses TDM with 24 slots/sec • 500 msec to establish end-to-end circuit Let’s work it out! • 640K / (1536K/24) + .5 = 10.5 sec Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  35. 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 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 Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  36. D E Packet Switching: Statistical Multiplexing 100 Mb/s Ethernet C A statistical multiplexing 1.5 Mb/s B queue of packets waiting for output link • Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand  statistical multiplexing. • Compare with TDM • Each host gets same slot in revolving TDM frame. Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  37. Packet-switching: Store-and-forward L R R R • 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 Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  38. Packet Switching versus Circuit Switching Packet switching allows more users to use network! N users 1 Mbps link Q: how did we get value 0.0004? • 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 0.0004 Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  39. Why 0.0004? Packet switching allows more users to use network! This is an application of Binomial Distribution. Find more information at http://en.wikipedia.org/wiki/Binomial_distribution • 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 0.0004 Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  40. Packet Switching versus Circuit Switching Is packet switching a “slam dunk winner?” • great for burst 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) Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  41. Tier-1 providers interconnect (peer) privately Internet structure: network of networks Tier 1 ISP Tier 1 ISP Tier 1 ISP • roughly hierarchical • at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage • treat each other as equals Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  42. Internet Structure: Network of Networks … … … … access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … Question: given millions of access ISPs, how to connect them together? Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  43. Internet Structure: Network of Networks … … … … Option: connect each access ISP to every other access ISP? connecting each access ISP to each other directly doesn’t scale: O(N2) connections. … … … … access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  44. Internet Structure: Network of Networks … … … … globalISP access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net Option: connect each access ISP to every other access ISP? Customer and provider ISPs have economic agreement. … … Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  45. Internet Structure: Network of Networks More Competitors! … … ISP B ISP A ISP C … … access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  46. Internet Structure: Network of Networks More Competitors, which should be connected Internet exchange point … … ISP B ISP C ISP A IXP IXP … … access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net peering link … … Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  47. Internet Structure: Network of Networks … and regional networks may arise to connect access nets to ISPS … … ISP B ISP C ISP A IXP IXP … … access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net regional net … … Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  48. Internet Structure: Network of Networks … and content provider networks (e.g., Google, Microsoft, Akamai ) may run their own network, to bring services, content close to end users … … ISP B ISP B ISP A IXP IXP … … Content provider network access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net regional net … … Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  49. Internet Structure: Network of Networks Tier 1 ISP Tier 1 ISP Google IXP IXP IXP Regional ISP Regional ISP access ISP access ISP access ISP access ISP access ISP access ISP access ISP access ISP Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

  50. POP: point-of-presence to/from backbone peering … …. … … … to/from customers Tier-1 ISP: e.g., Sprint Fall 2014 COMP 4605/5605 Department of Mathematics and Physics Donghyun (David) Kim North Carolina Central University

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