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 1.3 Network core 1.4 Network access and physical media 1.5 I...
What’s the Internet: “nuts and bolts” view  millions of connected            router                                      ...
“Cool” internet appliances                                              Web-enabled toaster +                             ...
What’s the Internet: “nuts and bolts” view   protocols control sending,             router     workstation    receiving o...
What’s the Internet: a service view  communication   infrastructure enables   distributed applications:       Web, email...
What’s a protocol?human protocols:           network protocols: “what’s the time?”        machines rather than “I have ...
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 1.3 Network core 1.4 Network access and physical media 1.5 I...
A closer look at network structure: network edge:  applications and  hosts network core:   routers   network of    net...
The network edge: end systems (hosts):     run application programs     e.g. Web, email     at “edge of network” clie...
Network edge: connection-oriented service Goal: data transfer              TCP service [RFC 793]   between end systems    ...
Network edge: connectionless service Goal: data transfer          App’s using TCP:   between end systems         HTTP (We...
Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 I...
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...
Another numerical example How long does it take to send a file of  640,000 bits from host A to host B over a  circuit-swi...
Network Core: Packet Switchingeach end-end data stream           resource contention:  divided into packets              ...
Packet Switching: Statistical Multiplexing        10 Mb/sA       Ethernet     statistical multiplexing   C                ...
Packet switching versus circuit switchingPacket switching allows more users to use network! 1 Mb/s link each user:    1...
Packet switching versus circuit switching Is packet switching a “slam dunk winner?”  Great for bursty data     resource ...
Packet-switching: store-and-forward              L                  R      R        R Takes L/R seconds to       Example:...
Packet-switched networks: forwarding   Goal: move packets through routers from source to    destination       we’ll stud...
Network Taxonomy                   Telecommunication                       networks     Circuit-switched                  ...
Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 I...
Access networks and physical media Q: How to connect end   systems to edge router?  residential access nets  institution...
Residential access: point to point access Dialup via modem    up to 56Kbps direct access to     router (often less)    ...
Residential access: cable modems  HFC: hybrid fiber coax     asymmetric: up to 30Mbps downstream, 2      Mbps upstream ...
Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html   Introduction   1-33
Cable Network Architecture: Overview                                   Typically 500 to 5,000 homes   cable headend       ...
Cable Network Architecture: Overview   cable headend                                   home             cable distribution...
Cable Network Architecture: Overview    server(s)   cable headend                                     home                ...
Cable Network Architecture: Overview           FDM:                                                                      C...
Company access: local area networks  company/univ local area   network (LAN) connects   end system to edge router  Ether...
Wireless access networks shared wireless access  network connects end system  to router                           router ...
Home networksTypical home network components: ADSL 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 1.3 Network core 1.4 Network access and physical media 1.5 I...
Internet structure: network of networks roughly hierarchical at center: “tier-1” ISPs (e.g., MCI, Sprint, AT&T, Cable  a...
Tier-1 ISP: e.g., SprintSprint US backbone network                                                              DS3 (45 Mb...
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...
UMass Campus Network                       Introduction   1-49
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 1.3 Network core 1.4 Network access and physical media 1.5 I...
How do loss and delay occur?packets queue in router buffers packet arrival rate to link exceeds output link capacity pac...
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 when packet arrives to full queue, packet i...
Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 I...
Protocol “Layers”Networks are complex! many “pieces”:   hosts                     Question:   routers                  ...
Organization of air travel    ticket (purchase)                 ticket (complain)    baggage (check)                   bag...
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...
source      message     M    application                                                Encapsulation    segment Ht    M  ...
Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 I...
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...
Introduction   1-74
Introduction: SummaryCovered a “ton” of material!   You now have: Internet overview             context, overview, what...
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  • Two simple multiple access control techniques. Each mobile’s share of the bandwidth is divided into portions for the uplink and the downlink. Also, possibly, out of band signaling. As we will see, used in AMPS, GSM, IS-54/136
  • 3rd edition chapter1

    1. 1. Chapter 1IntroductionA note on the use of these ppt slides:We’re making these slides freely available to all (faculty, students, readers). Computer Networking: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 A Top Down Approachrepresent a lot of work on our part. In return for use, we only ask the Featuring the Internet,following: If you use these slides (e.g., in a class) in substantially unaltered form,that you mention their source (after all, we’d like people to use our book!) 3rd edition. 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, and Jim Kurose, Keith Rossnote our copyright of this material. Addison-Wesley, JulyThanks and enjoy! JFK/KWR 2004.All material copyright 1996-2005J.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 later in course  network core approach:  access net, physical media  use Internet as  Internet/ISP structure example  performance: loss, delay  protocol layers, service models  network modeling Introduction 1-2
    3. 3. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Introduction 1-3
    4. 4. What’s the Internet: “nuts and bolts” view  millions of connected router workstation computing devices: hosts server = end systems mobile  running network apps local ISP  communication links  fiber, copper, radio, satellite regional ISP  transmission rate = bandwidth  routers: forward packets (chunks of data) company network 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 protocols control sending, router workstation receiving of msgs server  e.g., TCP, IP, HTTP, FTP, PPP mobile Internet: “network of local ISP networks”  loosely hierarchical  public Internet versus regional ISP private intranet Internet standards  RFC: Request for comments  IETF: Internet Engineering Task Force company network Introduction 1-6
    7. 7. What’s the Internet: a service view  communication infrastructure enables distributed applications:  Web, email, games, e- commerce, file sharing  communication services provided to apps:  Connectionless unreliable  connection-oriented reliable 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 taken protocols define format, when msgs received, order of msgs sent and or other events received among network 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 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Introduction 1-10
    11. 11. A closer look at network structure: network edge: applications and hosts network core:  routers  network of networks access networks, physical media: communication links Introduction 1-11
    12. 12. The network edge: 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 peer-peer model:  minimal (or no) use of dedicated servers  e.g. Gnutella, KaZaA, Skype Introduction 1-12
    13. 13. Network edge: connection-oriented service Goal: data transfer TCP service [RFC 793] between end systems  reliable, in-order byte-  handshaking: setup stream data transfer (prepare for) data  loss: acknowledgements transfer ahead of time and retransmissions  Hello, hello back human  flow control: protocol  sender won’t overwhelm  set up “state” in two receiver communicating hosts  congestion control:  TCP - Transmission  senders “slow down sending Control Protocol rate” when network  Internet’s connection- congested oriented service Introduction 1-13
    14. 14. Network edge: connectionless service Goal: data transfer App’s using TCP: between end systems  HTTP (Web), FTP (file  same as before! transfer), Telnet  UDP - User Datagram (remote login), SMTP Protocol [RFC 768]: (email)  connectionless  unreliable data App’s using UDP: transfer  streaming media,  no flow control teleconferencing, DNS,  no congestion control Internet telephony Introduction 1-14
    15. 15. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Introduction 1-15
    16. 16. 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 1-16
    17. 17. 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 1-17
    18. 18. 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 pieceidle if not used by owning call (no sharing) Introduction 1-18
    19. 19. Circuit Switching: FDM and TDM Example:FDM 4 users frequency timeTDM frequency time Introduction 1-19
    20. 20. 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 1-20
    21. 21. Another 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 FDM with 24 channels/frequencies  500 msec to establish end-to-end circuitLet’s work it out! Introduction 1-21
    22. 22. 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 1-22
    23. 23. Packet Switching: Statistical Multiplexing 10 Mb/sA 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, shared on demand ² statistical multiplexing.TDM: each host gets same slot in revolving TDM frame. Introduction 1-23
    24. 24. 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 less than .0004 Introduction 1-24
    25. 25. 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 1-25
    26. 26. 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 or R bps  delay = 15 sec Entire packet must arrive at router before it can be transmitted on next link: store and forward delay = 3L/R (assuming more on delay shortly … zero propagation delay) Introduction 1-26
    27. 27. Packet-switched networks: forwarding Goal: move packets through routers from source to destination  we’ll study several path selection (i.e. routing) algorithms (chapter 4) datagram network:  destination address in packet determines next hop  routes may change during session  analogy: driving, asking directions virtual circuit network:  each packet carries tag (virtual circuit ID), tag determines next hop  fixed path determined at call setup time, remains fixed thru call  routers maintain per-call state Introduction 1-27
    28. 28. Network Taxonomy Telecommunication networks Circuit-switched Packet-switched networks networks FDM Networks Datagram TDM with VCs Networks • Datagram network is not either connection-oriented or connectionless. • Internet provides both connection-oriented (TCP) and connectionless services (UDP) to apps. Introduction 1-28
    29. 29. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Introduction 1-29
    30. 30. 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 1-30
    31. 31. Residential access: point to point access 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” ADSL: asymmetric digital subscriber line  up to 1 Mbps upstream (today typically < 256 kbps)  up to 8 Mbps downstream (today typically < 1 Mbps)  FDM: 50 kHz - 1 MHz for downstream 4 kHz - 50 kHz for upstream 0 kHz - 4 kHz for ordinary telephone Introduction 1-31
    32. 32. Residential access: cable modems  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  deployment: available via cable TV companies Introduction 1-32
    33. 33. Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html Introduction 1-33
    34. 34. Cable Network Architecture: Overview Typically 500 to 5,000 homes cable headend home cable distribution network (simplified) Introduction 1-34
    35. 35. Cable Network Architecture: Overview cable headend home cable distribution network (simplified) Introduction 1-35
    36. 36. Cable Network Architecture: Overview server(s) cable headend home cable distribution network Introduction 1-36
    37. 37. Cable Network Architecture: Overview FDM: 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 1-37
    38. 38. Company access: local area networks  company/univ local area network (LAN) connects end system to edge router  Ethernet:  shared or dedicated link connects end system and router  10 Mbs, 100Mbps, Gigabit Ethernet  LANs: chapter 5 Introduction 1-38
    39. 39. 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 (WiFi): 11 Mbps wider-area wireless access  provided by telco operator  3G ~ 384 kbps mobile • Will it happen?? hosts  WAP/GPRS in Europe Introduction 1-39
    40. 40. Home networksTypical home network components: ADSL 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 1-40
    41. 41. 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 1-41
    42. 42. 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 transmission (e.g.,  legacy Ethernet 10’s-100’s Gps)  broadband:  low error rate: repeaters  multiple channels on spaced far apart ; immune cable to electromagnetic noise  HFC Introduction 1-42
    43. 43. 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  2Mbps, 11Mbps, 54 Mbps  propagation  wide-area (e.g., cellular) environment effects:  e.g. 3G: hundreds of kbps  reflection  satellite  obstruction by objects  Kbps to 45Mbps channel (or  interference multiple smaller channels)  270 msec end-end delay  geosynchronous versus low altitude Introduction 1-43
    44. 44. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Introduction 1-44
    45. 45. Internet structure: network of networks roughly hierarchical at center: “tier-1” ISPs (e.g., MCI, Sprint, AT&T, Cable and Wireless), national/international coverage  treat each other as equals Tier-1 providers also interconnect Tier-1 at public network providers Tier 1 ISP NAP access points interconnect (NAPs) (peer) privately Tier 1 ISP Tier 1 ISP Introduction 1-45
    46. 46. Tier-1 ISP: e.g., SprintSprint US backbone network DS3 (45 Mbps) OC3 (155 Mbps) OC12 (622 Mbps) OC48 (2.4 Gbps) Seattle Tacoma New York Stockton Cheyenne Chicago Pennsauken Relay San Jose Roachdale Wash. DC Kansas City Anaheim Atlanta Fort Worth Orlando Introduction 1-46
    47. 47. 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 NAP interconnect tier-2 ISP is at NAPcustomer oftier-1 provider Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Introduction 1-47
    48. 48. 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 tier NAPISPsconnectingthem 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 1-48
    49. 49. UMass Campus Network Introduction 1-49
    50. 50. 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 NAP Tier 1 ISP Tier 1 ISP Tier-2 ISP local Tier-2 ISP Tier-2 ISP ISP local local local ISP ISP ISP Introduction 1-50
    51. 51. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Introduction 1-51
    52. 52. How do loss and delay occur?packets queue in router buffers packet arrival rate to link exceeds output link capacity packets queue, wait for turn packet being transmitted (delay) A B packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction 1-52
    53. 53. 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 transmission A propagation B nodal processing queueing Introduction 1-53
    54. 54. 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 different quantities! transmissionA propagation B nodal processing queueing Introduction 1-54
    55. 55. 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 a car 12*10 = 120 sec (transmission 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 1-55
    56. 56. 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 1-56
    57. 57. 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 1-57
    58. 58. 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 1-58
    59. 59. “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 1-59
    60. 60. “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 1-60
    61. 61. Packet loss queue (aka buffer) preceding link in buffer has finite capacity when packet arrives to full queue, packet is dropped (aka lost) lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all Introduction 1-61
    62. 62. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Introduction 1-62
    63. 63. 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 1-63
    64. 64. 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 1-64
    65. 65. 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 1-65
    66. 66. 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 1-66
    67. 67. Internet protocol stack application: supporting network applications application  FTP, SMTP, HTTP transport: host-host data transfer transport  TCP, UDP network: routing of datagrams from network source to destination  IP, routing protocols link link: data transfer between neighboring network elements physical  PPP, Ethernet physical: bits “on the wire” Introduction 1-67
    68. 68. source message M application Encapsulation segment Ht M transportdatagram Hn Ht M networkframe Hl Hn Ht M link physical Hl Hn Ht M link Hl Hn Ht M physical switch destination Hn Ht M network Hn Ht M M application Hl Hn Ht M link Hl Hn Ht M Ht M transport physical Hn Ht M networkHl Hn Ht M link router physical Introduction 1-68
    69. 69. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Introduction 1-69
    70. 70. 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 1-70
    71. 71. 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 1-71
    72. 72. 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 1-72
    73. 73. 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 1-73
    74. 74. Introduction 1-74
    75. 75. 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/ISP structure performance: loss, delay layering and service models history Introduction 1-75

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