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Chapter 1IntroductionA note on the use of these ppt slides:We’re making these slides freely available to all (faculty, stu...
Chapter 1: IntroductionOur goal:              Overview: get “feel” and        what’s the Internet?  terminology         ...
Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge     end systems, access networks, links 1.3 Network core   ...
What’s the Internet: “nuts and bolts” view PC        millions of connected   Mobile network server     computing devices:...
“Cool” internet appliances                                              Web-enabled toaster +                             ...
What’s the Internet: “nuts and bolts” view                                      Mobile network   protocols control sendin...
What’s the Internet: a service view communication  infrastructure enables  distributed applications:    Web, VoIP, email...
What’s a protocol?human protocols:        network protocols: “what’s the time?”     machines rather than “I have a ques...
What’s a protocol?a human protocol and a computer network protocol:       Hi                               TCP connection ...
Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge     end systems, access networks, links 1.3 Network core   ...
A closer look at network structure: network edge:  applications and  hosts access networks,  physical media:  wired, wir...
The network edge: end systems (hosts):     run application programs     e.g. Web, email     at “edge of network”      ...
Access networks and physical media Q: How to connect end   systems to edge router?  residential access nets  institution...
Dial-up Modem            modem                           (e.g., AOL)     PC                                     modem     ...
Digital Subscriber Line (DSL)    PC    home                                    office              modem                 c...
Residential access: cable modems  Does not use telephone infrastructure     Instead uses cable TV infrastructure  HFC: ...
Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html   Introduction   1-17
Cable Network Architecture: Overview                                   Typically 500 to 5,000 homes   cable headend       ...
Cable Network Architecture: Overview    server(s)   cable headend                                     home                ...
Cable Network Architecture: Overview   cable headend                                   home             cable distribution...
Cable Network Architecture: Overview    FDM (more shortly):                                                               ...
Fiber to the Home                                                             ONT             central office             s...
Ethernet Internet access               100 Mbps                 Institutional                                        route...
Wireless access networks shared wireless access  network connects end system  to router                               rou...
Home networksTypical home network components: DSL or cable modem router/firewall/NAT Ethernet wireless access  point  ...
Physical Media                                    Twisted Pair (TP) Bit: propagates between            two insulated cop...
Physical Media: coax, fiber Coaxial cable:                   Fiber optic cable:  two concentric copper           glass f...
Physical media: radio  signal carried in             Radio link types:   electromagnetic                terrestrial micr...
Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge     end systems, access networks, links 1.3 Network core   ...
The Network Core mesh of interconnected  routers the fundamental  question: how is data  transferred through net?    ci...
Network Core: Circuit SwitchingEnd-end resources  reserved for “call” link bandwidth, switch  capacity dedicated resourc...
Network Core: Circuit Switchingnetwork resources              dividing link bandwidth  (e.g., bandwidth)             into...
Circuit Switching: FDM and TDM                         Example:FDM                         4 users      frequency         ...
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 ne...
Network Core: Packet Switchingeach end-end data stream           resource contention:  divided into packets              ...
Packet Switching: Statistical Multiplexing         100 Mb/s A       Ethernet     statistical multiplexing   C             ...
Packet-switching: store-and-forward              L                  R      R        R takes L/R seconds to       Example:...
Packet switching versus circuit switchingPacket switching allows more users to use network!  1 Mb/s link  each user:    ...
Packet switching versus circuit switching Is packet switching a “slam dunk winner?”  great for bursty data     resource ...
Internet structure: network of networks roughly hierarchical at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T,  Cab...
Tier-1 ISP: e.g., Sprint       POP: point-of-presence           to/from backbone                       peering       …    ...
Internet structure: network of networks  “Tier-2” ISPs: smaller (often regional) ISPs     Connect to one or more tier-1 ...
Internet structure: network of networks  “Tier-3” ISPs and local ISPs     last hop (“access”) network (closest to end sy...
Internet structure: network of networks a packet passes through many networks!           local            ISP     Tier 3 ...
Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge     end systems, access networks, links 1.3 Network core   ...
How do loss and delay occur?packets queue in router buffers packet arrival rate to link exceeds output link  capacity pa...
Four sources of packet delay 1. nodal processing:            2. queueing    check bit errors                time waiti...
Delay in packet-switched networks3. Transmission delay:         4. Propagation delay: R=link bandwidth (bps)        d = ...
Caravan analogy                          100 km               100 km      ten-car     toll                toll      carava...
Caravan analogy (more)                           100 km                    100 km     ten-car    toll                     ...
Nodal delay            d nodal = d proc + d queue + d trans + d prop dproc = processing delay      typically a few micro...
Queueing delay (revisited) R=link bandwidth (bps) L=packet length (bits) a=average packet  arrival rate traffic intensi...
“Real” Internet delays and routes What do “real” Internet delay & loss look like? Traceroute program: provides delay  me...
“Real” Internet delays and routestraceroute: gaia.cs.umass.edu to www.eurecom.fr                                    Three ...
Packet loss queue (aka buffer) preceding link in buffer has  finite capacity packet arriving to full queue dropped (aka ...
Throughput     throughput: rate (bits/time unit) at which      bits transferred between sender/receiver        instantan...
Throughput (more)  Rs   < Rc What is average end-end throughput?               Rs bits/sec             Rc bits/sec  Rs  ...
Throughput: Internet scenario                                     Rs per-connection                             Rs       ...
Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge     end systems, access networks, links 1.3 Network core   ...
Protocol “Layers”Networks are complex! many “pieces”:   hosts                              Question:   routers         ...
Organization of air travel    ticket (purchase)                     ticket (complain)    baggage (check)                  ...
Layering of airline functionalityticket (purchase)                                            ticket (complain)         ti...
Why layering?Dealing with complex systems: explicit structure allows identification,  relationship of complex system’s pi...
Internet protocol stack application: supporting network  applications                         application      FTP, SMTP...
ISO/OSI reference model presentation: allow applications to  interpret meaning of data, e.g.,      application  encryptio...
message      M                         source                       application                                           ...
Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge     end systems, access networks, links 1.3 Network core   ...
Network Security The field of network security is about:    how bad guys can attack computer networks    how we can def...
Bad guys can put malware intohosts via Internet Malware can get in host from a virus, worm, or  trojan horse. Spyware ma...
Bad guys can put malware intohosts via Internet Trojan horse                   Worm:    Hidden part of some           ...
Bad guys can attack servers and     network infrastructure  Denial of service (DoS): attackers make resources      (serve...
The bad guys can sniff packetsPacket sniffing:   broadcast media (shared Ethernet, wireless)   promiscuous network inter...
The bad guys can use false sourceaddresses IP   spoofing: send packet with false source address        A                 ...
The bad guys can record andplayback record-and-playback: sniff sensitive info (e.g.,  password), and use later    passwo...
Network Security more throughout this course chapter 8: focus on security crypographic techniques: obvious uses and  no...
Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge     end systems, access networks, links 1.3 Network core   ...
Internet History1961-1972: Early packet-switching principles 1961: Kleinrock - queueing    1972:  theory shows          ...
Internet History    1972-1980: Internetworking, new and proprietary nets 1970: ALOHAnet satellite                        ...
Internet History1980-1990: new protocols, a proliferation of networks 1983: deployment of       new national networks:  ...
Internet History1990, 2000’s: commercialization, the Web, new apps Early 1990’s: ARPAnet             Late 1990’s – 2000’s...
Internet History2007: ~500 million hosts Voice, Video over IP P2P applications: BitTorrent  (file sharing) Skype (VoIP)...
Introduction: SummaryCovered a “ton” of material!                               You now have: Internet overview          ...
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Chapter1 intro

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Chapter1 intro

  1. 1. Chapter 1IntroductionA note on the use of these ppt slides:We’re making these slides freely available to all (faculty, students, readers).They’re in PowerPoint form so you can add, modify, and delete slides(including this one) and slide content to suit your needs. They obviously Computer Networking:represent a lot of work on our part. In return for use, we only ask the A Top Down Approach ,following: If you use these slides (e.g., in a class) in substantially unaltered form, 5th edition.that you mention their source (after all, we’d like people to use our book!) Jim Kurose, Keith Ross Addison-Wesley, April If you post any slides in substantially unaltered form on a www site, thatyou note that they are adapted from (or perhaps identical to) our slides, andnote our copyright of this material. 2009.Thanks and enjoy! JFK/KWRAll material copyright 1996-2009J.F Kurose and K.W. Ross, All Rights Reserved Introduction 1-1
  2. 2. Chapter 1: IntroductionOur goal: Overview: get “feel” and  what’s the Internet? terminology  what’s a protocol? more depth, detail  network edge; hosts, access later in course approach: net, physical media  use Internet as  network core: packet/circuit example switching, Internet structure  performance: loss, delay, throughput  security  protocol layers, service models  history Introduction 1-2
  3. 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 1.7 History Introduction 1-3
  4. 4. What’s the Internet: “nuts and bolts” view PC  millions of connected Mobile network server computing devices: Global ISP wireless hosts = end systems laptop  running network cellular handheld apps Home network Regional ISP  communication links access  fiber, copper, points wired radio, satellite Institutional network links  transmission rate = bandwidth router  routers: forward packets (chunks of data) Introduction 1-4
  5. 5. “Cool” internet appliances Web-enabled toaster + weather forecaster IP picture frame http://www.ceiva.com/World’s smallest web serverhttp://www-ccs.cs.umass.edu/~shri/iPic.html Internet phones Introduction 1-5
  6. 6. What’s the Internet: “nuts and bolts” view Mobile network protocols control sending, receiving of msgs Global ISP  e.g., TCP, IP, HTTP, Skype, Ethernet Home network Internet: “network of networks” Regional ISP  loosely hierarchical  public Internet versus Institutional network private intranet Internet standards  RFC: Request for comments  IETF: Internet Engineering Task Force Introduction 1-6
  7. 7. What’s the Internet: a service view 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 Introduction 1-7
  8. 8. What’s a protocol?human protocols: network protocols: “what’s the time?”  machines rather than “I have a question” humans introductions  all communication activity in Internet governed by protocols… specific msgs sent… specific actions protocols define format, taken when msgs order of msgs sent and received, or other received among network events entities, and actions taken on msg transmission, receipt Introduction 1-8
  9. 9. What’s a protocol?a human protocol and a computer network protocol: Hi TCP connection request Hi TCP connection Got the response time? Get http://www.awl.com/kurose-ross 2:00 <file> time Q: Other human protocols? Introduction 1-9
  10. 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 1.7 History Introduction 1-10
  11. 11. A closer look at network structure: network edge: applications and hosts access networks, physical media: wired, wireless communication links network core:  interconnected routers  network of networks Introduction 1-11
  12. 12. The network edge: end systems (hosts):  run application programs  e.g. Web, email  at “edge of network” peer-peer client/server model  client host requests, receives service from always-on server client/server  e.g. Web browser/server; email client/server peer-peer model:  minimal (or no) use of dedicated servers  e.g. Skype, BitTorrent Introduction 1-12
  13. 13. Access networks and physical media 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? Introduction 1-13
  14. 14. Dial-up Modem modem (e.g., AOL) PC modem dial-up home ISP home network Internet telephone office central  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”
  15. 15. Digital Subscriber Line (DSL) PC home office modem central DSL splitter network telephone DSLAM phone downstream data home upstream data; 50KHz-1MHz 0-4KHz phone; 4-50KHz Existing phone line: Internet Also uses existing telephone infrastruture 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
  16. 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 Introduction 1-16
  17. 17. Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html Introduction 1-17
  18. 18. Cable Network Architecture: Overview Typically 500 to 5,000 homes cable headend home cable distribution network (simplified) Introduction 1-18
  19. 19. Cable Network Architecture: Overview server(s) cable headend home cable distribution network Introduction 1-19
  20. 20. Cable Network Architecture: Overview cable headend home cable distribution network (simplified) Introduction 1-20
  21. 21. Cable Network Architecture: Overview FDM (more shortly): C O V V V V V V N I I I I I I D D T D D D D D D A A R E E E E E E T T O O O O O O O A A L 1 2 3 4 5 6 7 8 9 Channels cable headend home cable distribution network Introduction 1-21
  22. 22. Fiber to the Home ONT central office splitter optical OLT fiber optical ONT fibers Internet optical ONT 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
  23. 23. Ethernet Internet access 100 Mbps Institutional router Ethernet To Institution’s switch ISP 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
  24. 24. Wireless access networks shared wireless access network connects end system to router router  via base station aka “access point” base wireless LANs: station  802.11b/g (WiFi): 11 or 54 Mbps wider-area wireless access  provided by telco operator  ~1Mbps over cellular system mobile (EVDO, HSDPA) hosts  next up (?): WiMAX (10’s Mbps) over wide area Introduction 1-24
  25. 25. Home networksTypical home network components: DSL or cable modem router/firewall/NAT Ethernet wireless access point wireless to/from laptops cable router/ cable modem firewall headend wireless access Ethernet point Introduction 1-25
  26. 26. Physical Media Twisted Pair (TP) Bit: propagates between  two insulated copper transmitter/rcvr pairs wires physical link: what lies  Category 3: traditional between transmitter & phone wires, 10 Mbps receiver Ethernet guided media:  Category 5: 100Mbps Ethernet  signals propagate in solid media: copper, fiber, coax unguided media:  signals propagate freely, e.g., radio Introduction 1-26
  27. 27. Physical Media: coax, fiber Coaxial cable: Fiber optic cable:  two concentric copper  glass fiber carrying light conductors pulses, each pulse a bit  bidirectional  high-speed operation:  baseband: high-speed point-to-point  single channel on cable  legacy Ethernet  low error rate: repeaters  broadband: spaced far apart ; immune  multiple channels on to electromagnetic noise cable  HFC Introduction 1-27
  28. 28. Physical media: radio  signal carried in Radio link types: electromagnetic  terrestrial microwave spectrum  e.g. up to 45 Mbps channels  no physical “wire”  LAN (e.g., Wifi)  bidirectional  11Mbps, 54 Mbps  propagation  wide-area (e.g., cellular) environment effects:  3G cellular: ~ 1 Mbps  reflection  satellite  obstruction by objects  Kbps to 45Mbps channel (or  interference multiple smaller channels)  270 msec end-end delay  geosynchronous versus low altitude Introduction 1-28
  29. 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 1.7 History Introduction 1-29
  30. 30. The Network Core 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” Introduction 1-30
  31. 31. Network Core: Circuit SwitchingEnd-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required Introduction 1-31
  32. 32. Network Core: Circuit Switchingnetwork resources  dividing link bandwidth (e.g., bandwidth) into “pieces” divided into “pieces”  frequency division pieces allocated to calls  time division resource piece idle if not used by owning call (no sharing) Introduction 1-32
  33. 33. Circuit Switching: FDM and TDM Example:FDM 4 users frequency timeTDM frequency time Introduction 1-33
  34. 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 circuitLet’s work it out! Introduction 1-34
  35. 35. Network Core: Packet Switchingeach end-end data stream resource contention: divided into packets  aggregate resource user A, B packets share demand can exceed network resources amount available each packet uses full link  congestion: packets bandwidth queue, wait for link use resources used as needed  store and forward: packets move one hop at a timeBandwidth division into “pieces”  Node receives complete Dedicated allocation packet before forwarding Resource reservation Introduction 1-35
  36. 36. Packet Switching: Statistical Multiplexing 100 Mb/s A Ethernet statistical multiplexing C 1.5 Mb/s B queue of packets waiting for output link D ESequence of A & B packets does not have fixed pattern, bandwidth shared on demand statistical multiplexing.TDM: each host gets same slot in revolving TDM frame. Introduction 1-36
  37. 37. Packet-switching: store-and-forward L R R R takes L/R seconds to Example: transmit (push out)  L = 7.5 Mbits packet of L bits on to  R = 1.5 Mbps link at R bps  transmission delay = 15 store and forward: sec entire packet must arrive at router before it can be transmitted on next link delay = 3L/R (assuming more on delay shortly … zero propagation delay) Introduction 1-37
  38. 38. Packet switching versus circuit switchingPacket switching allows more users to use network!  1 Mb/s link  each user:  100 kb/s when “active”  active 10% of time N users  circuit-switching: 1 Mbps link  10 users  packet switching:  with 35 users, Q: how did we get value 0.0004? probability > 10 active at same time is less than .0004 Introduction 1-38
  39. 39. Packet switching versus circuit switching Is packet switching a “slam dunk winner?”  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)Q: human analogies of reserved resources (circuitswitching) versus on-demand allocation (packet-switching)? Introduction 1-39
  40. 40. Internet structure: network of networks roughly hierarchical at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage  treat each other as equals Tier-1 providers Tier 1 ISP interconnect (peer) privately Tier 1 ISP Tier 1 ISP Introduction 1-40
  41. 41. Tier-1 ISP: e.g., Sprint POP: point-of-presence to/from backbone peering … … . … … … to/from customers Introduction 1-41
  42. 42. Internet structure: network of networks  “Tier-2” ISPs: smaller (often regional) ISPs  Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier-2 ISPsTier-2 ISP pays Tier-2 ISP also peer Tier-2 ISP privately withtier-1 ISP forconnectivity to Tier 1 ISP each other.rest of Internet tier-2 ISP iscustomer oftier-1 provider Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Introduction 1-42
  43. 43. Internet structure: network of networks  “Tier-3” ISPs and local ISPs  last hop (“access”) network (closest to end systems) local ISP Tier 3 local local local ISP ISP ISP ISPLocal and tier- Tier-2 ISP Tier-2 ISP3 ISPs arecustomers of Tier 1 ISPhigher tierISPsconnectingthem to rest Tier 1 ISP Tier 1 ISP Tier-2 ISPof Internet local Tier-2 ISP Tier-2 ISP ISP local local local ISP ISP ISP Introduction 1-43
  44. 44. Internet structure: network of networks a packet passes through many networks! local ISP Tier 3 local local local ISP ISP ISP ISP Tier-2 ISP Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP local Tier-2 ISP Tier-2 ISP ISP local local local ISP ISP ISP Introduction 1-44
  45. 45. 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 1-45
  46. 46. How do loss and delay occur?packets queue in router buffers packet arrival rate to link exceeds output link capacity packets queue, wait for turnA packet being transmitted (delay) packets queueing (delay) B free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction 1-46
  47. 47. Four sources of packet delay 1. nodal processing:  2. queueing  check bit errors  time waiting at output  determine output link link for transmission  depends on congestion level of router processing queueing nodal B propagation A transmission Introduction 1-47
  48. 48. Delay in packet-switched networks3. Transmission delay: 4. Propagation delay: R=link bandwidth (bps)  d = length of physical link L=packet length (bits)  s = propagation speed in time to send bits into medium (~2x108 m/sec) link = L/R  propagation delay = d/s Note: s and R are very processing queueing different quantities! nodal B propagationA transmission Introduction 1-48
  49. 49. Caravan analogy 100 km 100 km ten-car toll toll caravan booth booth cars “propagate” at  Time to “push” entire 100 km/hr caravan through toll toll booth takes 12 sec to booth onto highway = service car (transmission 12*10 = 120 sec time)  Time for last car to car~bit; caravan ~ packet propagate from 1st to 2nd toll both: 100km/ Q: How long until caravan (100km/hr)= 1 hr is lined up before 2nd toll  A: 62 minutes booth? Introduction 1-49
  50. 50. Caravan analogy (more) 100 km 100 km ten-car toll toll caravan booth booth  Yes! After 7 min, 1st car Cars now “propagate” at at 2nd booth and 3 cars still at 1st booth. 1000 km/hr  1st bit of packet can Toll booth now takes 1 arrive at 2nd router min to service a car before packet is fully Q: Will cars arrive to transmitted at 1st router! 2nd booth before all  See Ethernet applet at AWL cars serviced at 1st Web site booth? Introduction 1-50
  51. 51. Nodal delay d nodal = d proc + d queue + d trans + d prop dproc = processing delay  typically a few microsecs or less dqueue = queuing delay  depends on congestion dtrans = transmission delay  = L/R, significant for low-speed links dprop = propagation delay  a few microsecs to hundreds of msecs Introduction 1-51
  52. 52. Queueing delay (revisited) R=link bandwidth (bps) L=packet length (bits) a=average packet arrival rate traffic intensity = La/R La/R ~ 0: average queueing delay small La/R -> 1: delays become large La/R > 1: more “work” arriving than can be serviced, average delay infinite! Introduction 1-52
  53. 53. “Real” Internet delays and routes What do “real” Internet delay & loss look like? Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i:  sends three packets that will reach router i on path towards destination  router i will return packets to sender  sender times interval between transmission and reply. 3 probes 3 probes 3 probes Introduction 1-53
  54. 54. “Real” Internet delays and routestraceroute: gaia.cs.umass.edu to www.eurecom.fr Three delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms trans-oceanic8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms link10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17 * * *18 * * * * means no response (probe lost, router not replying)19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms Introduction 1-54
  55. 55. Packet loss queue (aka buffer) preceding link in buffer has finite capacity packet arriving to full queue dropped (aka lost) lost packet may be retransmitted by previous node, by source end system, or not at all buffer (waiting area) packet being transmitted A B packet arriving to full buffer is lost Introduction 1-55
  56. 56. Throughput  throughput: rate (bits/time unit) at which bits transferred between sender/receiver  instantaneous: rate at given point in time  average: rate over longer period of time link capacityserver sends bits pipe that can carry server, with link capacity pipe that can carry (fluid) of F bits file into pipe fluid at rate Rs bits/sec Rfluid at rate c bits/sec to send to client Rs bits/sec) Rc bits/sec) Introduction 1-56
  57. 57. Throughput (more)  Rs < Rc What is average end-end throughput? Rs bits/sec Rc bits/sec  Rs > Rc What is average end-end throughput? Rs bits/sec Rc bits/sec bottleneck linklink on end-end path that constrains end-end throughput Introduction 1-57
  58. 58. Throughput: Internet scenario Rs per-connection Rs Rs end-end throughput: R min(Rc,Rs,R/10) in practice: Rc or Rs Rc Rc is often bottleneck Rc 10 connections (fairly) share backbone bottleneck link R bits/sec Introduction 1-58
  59. 59. 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 1-59
  60. 60. Protocol “Layers”Networks are complex! many “pieces”:  hosts Question:  routers Is there any hope of  links of various organizing structure of media network?  applications  protocols Or at least our discussion  hardware, of networks? software Introduction 1-60
  61. 61. Organization of air travel ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing airplane routing airplane routing  a series of steps Introduction 1-61
  62. 62. Layering of airline functionalityticket (purchase) ticket (complain) ticketbaggage (check) baggage (claim baggage gates (load) gates (unload) gaterunway (takeoff) runway (land) takeoff/landingairplane routing airplane routing airplane routing airplane routing airplane routing departure intermediate air-traffic arrival airport control centers airportLayers: each layer implements a service  via its own internal-layer actions  relying on services provided by layer below Introduction 1-62
  63. 63. 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  e.g., change in gate procedure doesn’t affect rest of system layering considered harmful? Introduction 1-63
  64. 64. Internet protocol stack application: supporting network applications application  FTP, SMTP, HTTP transport: process-process data transport transfer  TCP, UDP network network: routing of datagrams from source to destination link  IP, routing protocols link: data transfer between physical neighboring network elements  PPP, Ethernet physical: bits “on the wire” Introduction 1-64
  65. 65. ISO/OSI reference model presentation: allow applications to interpret meaning of data, e.g., application encryption, compression, machine- presentation specific conventions session: synchronization, session checkpointing, recovery of data transport exchange network Internet stack “missing” these layers! link  these services, if needed, must physical be implemented in application  needed? Introduction 1-65
  66. 66. message M source application Encapsulation segment Ht M transportdatagram Hn Ht M networkframe Hl Hn Ht M link physical link physical switch destination Hn Ht M network M application Hl Hn Ht M link Hn Ht M Ht M transport physical Hn Ht M networkHl Hn Ht M link router physical Introduction 1-66
  67. 67. 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 1-67
  68. 68. Network Security The field of network security is about:  how bad guys can attack computer networks  how we can defend networks against attacks  how to design architectures that are immune to attacks Internet not originally designed with (much) security in mind  original vision: “a group of mutually trusting users attached to a transparent network”   Internet protocol designers playing “catch-up”  Security considerations in all layers! Introduction 1-68
  69. 69. Bad guys can put malware intohosts via Internet Malware can get in host from a virus, worm, or trojan horse. Spyware malware can record keystrokes, web sites visited, upload info to collection site. Infected host can be enrolled in a botnet, used for spam and DDoS attacks. Malware is often self-replicating: from an infected host, seeks entry into other hosts Introduction 1-69
  70. 70. Bad guys can put malware intohosts via Internet Trojan horse  Worm:  Hidden part of some  infection by passively otherwise useful receiving object that gets software itself executed  Today often on a Web  self- replicating: propagates page (Active-X, plugin) to other hosts, users Virus Sapphire Worm: aggregate scans/sec in first 5 minutes of outbreak (CAIDA, UWisc data)  infection by receiving object (e.g., e-mail attachment), actively executing  self-replicating: propagate itself to other hosts, users Introduction 1-70
  71. 71. Bad guys can attack servers and network infrastructure  Denial of service (DoS): attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic1. select target2. break into hosts around the network (see botnet)3. send packets toward target from target compromised hosts Introduction 1-71
  72. 72. The bad guys can sniff packetsPacket sniffing:  broadcast media (shared Ethernet, wireless)  promiscuous network interface reads/records all packets (e.g., including passwords!) passing by A C src:B dest:A payload B  Wireshark software used for end-of-chapter labs is a (free) packet-sniffer Introduction 1-72
  73. 73. The bad guys can use false sourceaddresses IP spoofing: send packet with false source address A C src:B dest:A payload B Introduction 1-73
  74. 74. The bad guys can record andplayback record-and-playback: sniff sensitive info (e.g., password), and use later  password holder is that user from system point of view C A src:B dest:A user: B; password: foo B Introduction 1-74
  75. 75. Network Security more throughout this course chapter 8: focus on security crypographic techniques: obvious uses and not so obvious uses Introduction 1-75
  76. 76. 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 1-76
  77. 77. Internet History1961-1972: Early packet-switching principles 1961: Kleinrock - queueing  1972: theory shows  ARPAnet public demonstration effectiveness of packet-  NCP (Network Control Protocol) switching first host-host protocol 1964: Baran - packet-  first e-mail program switching in military nets  ARPAnet has 15 nodes 1967: ARPAnet conceived by Advanced Research Projects Agency 1969: first ARPAnet node operational Introduction 1-77
  78. 78. Internet History 1972-1980: Internetworking, new and proprietary nets 1970: ALOHAnet satellite Cerf and Kahn’s internetworking network in Hawaii principles: 1974: Cerf and Kahn -  minimalism, autonomy - no architecture for internal changes required interconnecting networks to interconnect networks  best effort service model 1976: Ethernet at Xerox PARC  stateless routers  decentralized control ate70’s: proprietary architectures: DECnet, SNA, define today’s Internet XNA architecture late 70’s: switching fixed length packets (ATM precursor) 1979: ARPAnet has 200 nodes Introduction 1-78
  79. 79. Internet History1980-1990: new protocols, a proliferation of networks 1983: deployment of  new national networks: TCP/IP Csnet, BITnet, 1982: smtp e-mail NSFnet, Minitel protocol defined  100,000 hosts 1983: DNS defined connected to for name-to-IP- confederation of address translation networks 1985: ftp protocol defined 1988: TCP congestion control Introduction 1-79
  80. 80. Internet History1990, 2000’s: commercialization, the Web, new apps Early 1990’s: ARPAnet Late 1990’s – 2000’s: decommissioned  more killer apps: instant 1991: NSF lifts restrictions on messaging, P2P file sharing commercial use of NSFnet  network security to (decommissioned, 1995) forefront early 1990s: Web  est. 50 million host, 100  hypertext [Bush 1945, Nelson million+ users 1960’s]  backbone links running at  HTML, HTTP: Berners-Lee Gbps  1994: Mosaic, later Netscape  late 1990’s: commercialization of the Web Introduction 1-80
  81. 81. Internet History2007: ~500 million hosts Voice, Video over IP P2P applications: BitTorrent (file sharing) Skype (VoIP), PPLive (video) more applications: YouTube, gaming wireless, mobility Introduction 1-81
  82. 82. Introduction: SummaryCovered a “ton” of material! You now have: Internet overview  context, overview, what’s a protocol? “feel” of networking network edge, core, access  more depth, detail to network follow!  packet-switching versus circuit-switching  Internet structure performance: loss, delay, throughput layering, service models security history Introduction 1-82

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