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Lecture No. 1.ppt

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MuhammadRizwanHaider2

This document provides an overview of key concepts in computer networking and the structure of the Internet. It begins with definitions of the Internet as a globally connected network of hosts, end systems, and routers. Data transmission occurs through various access networks to residential, institutional, or mobile end systems and then through the network core. In the core, routers forward packets via packet switching, where data is broken into packets that are transmitted over shared network links. The Internet structure is described as a hierarchical "network of networks" with different tiers of Internet service providers. The document outlines various networking technologies and concepts to be covered in more depth later.

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Introduction 1-1 Chapter 1 Introduction Computer Networking: A Top Down Approach , 4th edition. Jim Kurose, Keith Ross Addison-Wesley, July 2007. Dr. Muhammad Asif
Introduction 1-2 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
Introduction 1-3 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 1-4 What’s the Internet: “nuts and bolts” view  millions of connected computing devices: hosts = end systems  running network apps Home network Institutional network Mobile network Global ISP Regional ISP router PC server wireless laptop cellular handheld wired links access points  communication links  fiber, copper, radio, satellite  transmission rate = bandwidth  routers: forward packets (chunks of data)
Introduction 1-5 “Cool” internet appliances World’s smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.html IP picture frame http://www.ceiva.com/ Web-enabled toaster + weather forecaster Internet phones
Introduction 1-6 What’s the Internet: “nuts and bolts” view  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 Home network Institutional network Mobile network Global ISP Regional ISP
Introduction 1-7 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 1-8 What’s a protocol? human protocols:  “what’s the time?”  “I have a question”  introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols:  machines rather than humans  all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt
Introduction 1-9 What’s a protocol? a human protocol and a computer network protocol: Q: Other human protocols? Hi Hi Got the time? 2:00 TCP connection request TCP connection response Get http://www.awl.com/kurose-ross <file> time
Introduction 1-10 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 1-11 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 1-12 The network edge:  end systems (hosts):  run application programs  e.g. Web, email  at “edge of network” client/server peer-peer  client/server model  client host requests, receives service from always-on server  e.g. Web browser/server; email client/server  peer-peer model:  minimal (or no) use of dedicated servers  e.g. Skype, BitTorrent
Introduction 1-13 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 1-14 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”  DSL: digital subscriber line  deployment: telephone company (typically)  up to 1 Mbps upstream (today typically < 256 kbps)  up to 8 Mbps downstream (today typically < 1 Mbps)  dedicated physical line to telephone central office
Introduction 1-15 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 1-16 Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
Introduction 1-17 Cable Network Architecture: Overview home cable headend cable distribution network (simplified) Typically 500 to 5,000 homes
Introduction 1-18 Cable Network Architecture: Overview home cable headend cable distribution network server(s)
Introduction 1-19 Cable Network Architecture: Overview home cable headend cable distribution network (simplified)
Introduction 1-20 Cable Network Architecture: Overview home cable headend cable distribution network Channels 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 D A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 FDM (more shortly):
Introduction 1-21 Company access: local area networks  company/univ local area network (LAN) connects end system to edge router  Ethernet:  10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet  modern configuration: end systems connect into Ethernet switch  LANs: chapter 5
Introduction 1-22 Wireless access networks  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 base station mobile hosts router
Introduction 1-23 Home networks Typical home network components:  DSL or cable modem  router/firewall/NAT  Ethernet  wireless access point wireless access point wireless laptops router/ firewall cable modem to/from cable headend Ethernet
Introduction 1-24 Physical Media  Bit: propagates between transmitter/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
Introduction 1-25 Physical Media: coax, fiber Coaxial cable:  two concentric copper conductors  bidirectional  baseband:  single channel on cable  legacy Ethernet  broadband:  multiple channels on cable  HFC 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
Introduction 1-26 Physical media: radio  signal carried in electromagnetic spectrum  no physical “wire”  bidirectional  propagation environment effects:  reflection  obstruction by objects  interference 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
Introduction 1-27 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 1-28 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 1-29 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
Introduction 1-30 Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces”  pieces allocated to calls  resource piece idle if not used by owning call (no sharing)  dividing link bandwidth into “pieces”  frequency division  time division
Introduction 1-31 Circuit Switching: FDM and TDM FDM frequency time TDM frequency time 4 users Example:
Introduction 1-32 Network Core: Packet Switching 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 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 Bandwidth division into “pieces” Dedicated allocation Resource reservation
Introduction 1-33 Packet Switching: Statistical Multiplexing Sequence 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. A B C 100 Mb/s Ethernet 1.5 Mb/s D E statistical multiplexing queue of packets waiting for output link
Introduction 1-34 Packet-switching: store-and-forward  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 R R R L more on delay shortly …
Introduction 1-35 Packet switching versus circuit switching  1 Mb/s link  each user:  100 kb/s when “active”  active 10% of time  circuit-switching:  10 users  packet switching:  with 35 users, probability > 10 active at same time is less than .0004 Packet switching allows more users to use network! N users 1 Mbps link Q: how did we get value 0.0004?
Introduction 1-36 Packet switching versus circuit switching  great for bursty data  resource sharing  simpler, no call setup  excessive congestion: packet delay and loss  protocols needed for reliable data transfer, congestion control  Q: How to provide circuit-like behavior?  bandwidth guarantees needed for audio/video apps  still an unsolved problem (chapter 7) Is packet switching a “slam dunk winner?” Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?
Introduction 1-37 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 ISP Tier 1 ISP Tier 1 ISP Tier-1 providers interconnect (peer) privately
Introduction 1-38 Tier-1 ISP: e.g., Sprint … to/from customers peering to/from backbone … . … … … POP: point-of-presence
Introduction 1-39 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 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet  tier-2 ISP is customer of tier-1 provider Tier-2 ISPs also peer privately with each other.
Introduction 1-40 Internet structure: network of networks  “Tier-3” ISPs and local ISPs  last hop (“access”) network (closest to end systems) Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet
Introduction 1-41 Internet structure: network of networks  a packet passes through many networks! Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP
Introduction 1-42 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 1-43 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 A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers
Introduction 1-44 Four sources of packet delay  1. nodal processing:  check bit errors  determine output link A B propagation transmission nodal processing queueing  2. queueing  time waiting at output link for transmission  depends on congestion level of router
Introduction 1-45 Delay in packet-switched networks 3. Transmission delay:  R=link bandwidth (bps)  L=packet length (bits)  time to send bits into link = L/R 4. Propagation delay:  d = length of physical link  s = propagation speed in medium (~2x108 m/sec)  propagation delay = d/s A B propagation transmission nodal processing queueing Note: s and R are very different quantities!
Introduction 1-46 Caravan analogy  cars “propagate” at 100 km/hr  toll booth takes 12 sec to service car (transmission time)  car~bit; caravan ~ packet  Q: How long until caravan is lined up before 2nd toll booth?  Time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec  Time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr)= 1 hr  A: 62 minutes toll booth toll booth ten-car caravan 100 km 100 km
Introduction 1-47 Caravan analogy (more)  Cars now “propagate” at 1000 km/hr  Toll booth now takes 1 min to service a car  Q: Will cars arrive to 2nd booth before all cars serviced at 1st booth?  Yes! After 7 min, 1st car at 2nd booth and 3 cars still at 1st booth.  1st bit of packet can arrive at 2nd router before packet is fully transmitted at 1st router!  See Ethernet applet at AWL Web site toll booth toll booth ten-car caravan 100 km 100 km
Introduction 1-48 Nodal delay  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 prop trans queue proc nodal d d d d d    
Introduction 1-49 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 1-50 “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 1-51 “Real” Internet delays and routes 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms traceroute: gaia.cs.umass.edu to www.eurecom.fr Three delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu * means no response (probe lost, router not replying) trans-oceanic link
Introduction 1-52 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 A B packet being transmitted packet arriving to full buffer is lost buffer (waiting area)
Introduction 1-53 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 server, with file of F bits to send to client link capacity Rs bits/sec link capacity Rc bits/sec pipe that can carry fluid at rate Rs bits/sec) pipe that can carry fluid at rate Rc bits/sec) server sends bits (fluid) into pipe
Introduction 1-54 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 link on end-end path that constrains end-end throughput bottleneck link
Introduction 1-55 Throughput: Internet scenario 10 connections (fairly) share backbone bottleneck link R bits/sec Rs Rs Rs Rc Rc Rc R  per-connection end-end throughput: min(Rc,Rs,R/10)  in practice: Rc or Rs is often bottleneck
Introduction 1-56 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 1-57 Protocol “Layers” Networks are complex!  many “pieces”:  hosts  routers  links of various media  applications  protocols  hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks?
Introduction 1-58 Organization of air travel  a series of steps ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing airplane routing
Introduction 1-59 ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers airplane routing airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing ticket baggage gate takeoff/landing airplane routing Layering of airline functionality Layers: each layer implements a service  via its own internal-layer actions  relying on services provided by layer below
Introduction 1-60 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 1-61 Internet protocol stack  application: supporting network applications  FTP, SMTP, HTTP  transport: process-process data transfer  TCP, UDP  network: routing of datagrams from source to destination  IP, routing protocols  link: data transfer between neighboring network elements  PPP, Ethernet  physical: bits “on the wire” application transport network link physical
Introduction 1-62 ISO/OSI reference model  presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine- specific conventions  session: synchronization, checkpointing, recovery of data exchange  Internet stack “missing” these layers!  these services, if needed, must be implemented in application  needed? application presentation session transport network link physical
Introduction 1-63 source application transport network link physical Ht Hn M segment Ht datagram destination application transport network link physical Ht Hn Hl M Ht Hn M Ht M M network link physical link physical Ht Hn Hl M Ht Hn M Ht Hn M Ht Hn Hl M router switch Encapsulation message M Ht M Hn frame
Introduction 1-64 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 1-65 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 1-66 Bad guys can put malware into hosts 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 1-67 Bad guys can put malware into hosts via Internet  Trojan horse  Hidden part of some otherwise useful software  Today often on a Web page (Active-X, plugin)  Virus  infection by receiving object (e.g., e-mail attachment), actively executing  self-replicating: propagate itself to other hosts, users  Worm:  infection by passively receiving object that gets itself executed  self- replicating: propagates to other hosts, users Sapphire Worm: aggregate scans/sec in first 5 minutes of outbreak (CAIDA, UWisc data)
Introduction 1-68 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 traffic 1. select target 2. break into hosts around the network (see botnet) 3. send packets toward target from compromised hosts target
Introduction 1-69 The bad guys can sniff packets Packet sniffing:  broadcast media (shared Ethernet, wireless)  promiscuous network interface reads/records all packets (e.g., including passwords!) passing by A B C src:B dest:A payload  Wireshark software used for end-of-chapter labs is a (free) packet-sniffer
Introduction 1-70 The bad guys can use false source addresses  IP spoofing: send packet with false source address A B C src:B dest:A payload
Introduction 1-71 The bad guys can record and playback  record-and-playback: sniff sensitive info (e.g., password), and use later  password holder is that user from system point of view A B C src:B dest:A user: B; password: foo
Introduction 1-72 Network Security  more throughout this course  chapter 8: focus on security  crypographic techniques: obvious uses and not so obvious uses
Introduction 1-73 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 1-74 Internet History  1961: Kleinrock - queueing theory shows effectiveness of packet- switching  1964: Baran - packet- switching in military nets  1967: ARPAnet conceived by Advanced Research Projects Agency  1969: first ARPAnet node operational  1972:  ARPAnet public demonstration  NCP (Network Control Protocol) first host-host protocol  first e-mail program  ARPAnet has 15 nodes 1961-1972: Early packet-switching principles
Introduction 1-75 Internet History  1970: ALOHAnet satellite network in Hawaii  1974: Cerf and Kahn - architecture for interconnecting networks  1976: Ethernet at Xerox PARC  ate70’s: proprietary architectures: DECnet, SNA, XNA  late 70’s: switching fixed length packets (ATM precursor)  1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles:  minimalism, autonomy - no internal changes required to interconnect networks  best effort service model  stateless routers  decentralized control define today’s Internet architecture 1972-1980: Internetworking, new and proprietary nets
Introduction 1-76 Internet History  1983: deployment of TCP/IP  1982: smtp e-mail protocol defined  1983: DNS defined for name-to-IP- address translation  1985: ftp protocol defined  1988: TCP congestion control  new national networks: Csnet, BITnet, NSFnet, Minitel  100,000 hosts connected to confederation of networks 1980-1990: new protocols, a proliferation of networks
Introduction 1-77 Internet History  Early 1990’s: ARPAnet decommissioned  1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)  early 1990s: Web  hypertext [Bush 1945, Nelson 1960’s]  HTML, HTTP: Berners-Lee  1994: Mosaic, later Netscape  late 1990’s: commercialization of the Web Late 1990’s – 2000’s:  more killer apps: instant messaging, P2P file sharing  network security to forefront  est. 50 million host, 100 million+ users  backbone links running at Gbps 1990, 2000’s: commercialization, the Web, new apps
Introduction 1-78 Internet History 2007:  ~500 million hosts  Voice, Video over IP  P2P applications: BitTorrent (file sharing) Skype (VoIP), PPLive (video)  more applications: YouTube, gaming  wireless, mobility
Introduction 1-79 Introduction: Summary Covered a “ton” of material!  Internet overview  what’s a protocol?  network edge, core, access network  packet-switching versus circuit-switching  Internet structure  performance: loss, delay, throughput  layering, service models  security  history You now have:  context, overview, “feel” of networking  more depth, detail to follow!

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Lecture No. 1.ppt

  • 1. Introduction 1-1 Chapter 1 Introduction Computer Networking: A Top Down Approach , 4th edition. Jim Kurose, Keith Ross Addison-Wesley, July 2007. Dr. Muhammad Asif
  • 2. Introduction 1-2 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
  • 3. Introduction 1-3 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
  • 4. Introduction 1-4 What’s the Internet: “nuts and bolts” view  millions of connected computing devices: hosts = end systems  running network apps Home network Institutional network Mobile network Global ISP Regional ISP router PC server wireless laptop cellular handheld wired links access points  communication links  fiber, copper, radio, satellite  transmission rate = bandwidth  routers: forward packets (chunks of data)
  • 5. Introduction 1-5 “Cool” internet appliances World’s smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.html IP picture frame http://www.ceiva.com/ Web-enabled toaster + weather forecaster Internet phones
  • 6. Introduction 1-6 What’s the Internet: “nuts and bolts” view  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 Home network Institutional network Mobile network Global ISP Regional ISP
  • 7. Introduction 1-7 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
  • 8. Introduction 1-8 What’s a protocol? human protocols:  “what’s the time?”  “I have a question”  introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols:  machines rather than humans  all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt
  • 9. Introduction 1-9 What’s a protocol? a human protocol and a computer network protocol: Q: Other human protocols? Hi Hi Got the time? 2:00 TCP connection request TCP connection response Get http://www.awl.com/kurose-ross <file> time
  • 10. Introduction 1-10 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
  • 11. Introduction 1-11 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
  • 12. Introduction 1-12 The network edge:  end systems (hosts):  run application programs  e.g. Web, email  at “edge of network” client/server peer-peer  client/server model  client host requests, receives service from always-on server  e.g. Web browser/server; email client/server  peer-peer model:  minimal (or no) use of dedicated servers  e.g. Skype, BitTorrent
  • 13. Introduction 1-13 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?
  • 14. Introduction 1-14 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”  DSL: digital subscriber line  deployment: telephone company (typically)  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
  • 15. Introduction 1-15 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
  • 16. Introduction 1-16 Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
  • 17. Introduction 1-17 Cable Network Architecture: Overview home cable headend cable distribution network (simplified) Typically 500 to 5,000 homes
  • 18. Introduction 1-18 Cable Network Architecture: Overview home cable headend cable distribution network server(s)
  • 19. Introduction 1-19 Cable Network Architecture: Overview home cable headend cable distribution network (simplified)
  • 20. Introduction 1-20 Cable Network Architecture: Overview home cable headend cable distribution network Channels 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 D A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 FDM (more shortly):
  • 21. Introduction 1-21 Company access: local area networks  company/univ local area network (LAN) connects end system to edge router  Ethernet:  10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet  modern configuration: end systems connect into Ethernet switch  LANs: chapter 5
  • 22. Introduction 1-22 Wireless access networks  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 base station mobile hosts router
  • 23. Introduction 1-23 Home networks Typical home network components:  DSL or cable modem  router/firewall/NAT  Ethernet  wireless access point wireless access point wireless laptops router/ firewall cable modem to/from cable headend Ethernet
  • 24. Introduction 1-24 Physical Media  Bit: propagates between transmitter/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
  • 25. Introduction 1-25 Physical Media: coax, fiber Coaxial cable:  two concentric copper conductors  bidirectional  baseband:  single channel on cable  legacy Ethernet  broadband:  multiple channels on cable  HFC 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
  • 26. Introduction 1-26 Physical media: radio  signal carried in electromagnetic spectrum  no physical “wire”  bidirectional  propagation environment effects:  reflection  obstruction by objects  interference 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
  • 27. Introduction 1-27 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
  • 28. Introduction 1-28 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”
  • 29. Introduction 1-29 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
  • 30. Introduction 1-30 Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces”  pieces allocated to calls  resource piece idle if not used by owning call (no sharing)  dividing link bandwidth into “pieces”  frequency division  time division
  • 31. Introduction 1-31 Circuit Switching: FDM and TDM FDM frequency time TDM frequency time 4 users Example:
  • 32. Introduction 1-32 Network Core: Packet Switching 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 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 Bandwidth division into “pieces” Dedicated allocation Resource reservation
  • 33. Introduction 1-33 Packet Switching: Statistical Multiplexing Sequence 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. A B C 100 Mb/s Ethernet 1.5 Mb/s D E statistical multiplexing queue of packets waiting for output link
  • 34. Introduction 1-34 Packet-switching: store-and-forward  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 R R R L more on delay shortly …
  • 35. Introduction 1-35 Packet switching versus circuit switching  1 Mb/s link  each user:  100 kb/s when “active”  active 10% of time  circuit-switching:  10 users  packet switching:  with 35 users, probability > 10 active at same time is less than .0004 Packet switching allows more users to use network! N users 1 Mbps link Q: how did we get value 0.0004?
  • 36. Introduction 1-36 Packet switching versus circuit switching  great for bursty data  resource sharing  simpler, no call setup  excessive congestion: packet delay and loss  protocols needed for reliable data transfer, congestion control  Q: How to provide circuit-like behavior?  bandwidth guarantees needed for audio/video apps  still an unsolved problem (chapter 7) Is packet switching a “slam dunk winner?” Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?
  • 37. Introduction 1-37 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 ISP Tier 1 ISP Tier 1 ISP Tier-1 providers interconnect (peer) privately
  • 38. Introduction 1-38 Tier-1 ISP: e.g., Sprint … to/from customers peering to/from backbone … . … … … POP: point-of-presence
  • 39. Introduction 1-39 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 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet  tier-2 ISP is customer of tier-1 provider Tier-2 ISPs also peer privately with each other.
  • 40. Introduction 1-40 Internet structure: network of networks  “Tier-3” ISPs and local ISPs  last hop (“access”) network (closest to end systems) Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet
  • 41. Introduction 1-41 Internet structure: network of networks  a packet passes through many networks! Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP
  • 42. Introduction 1-42 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
  • 43. Introduction 1-43 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 A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers
  • 44. Introduction 1-44 Four sources of packet delay  1. nodal processing:  check bit errors  determine output link A B propagation transmission nodal processing queueing  2. queueing  time waiting at output link for transmission  depends on congestion level of router
  • 45. Introduction 1-45 Delay in packet-switched networks 3. Transmission delay:  R=link bandwidth (bps)  L=packet length (bits)  time to send bits into link = L/R 4. Propagation delay:  d = length of physical link  s = propagation speed in medium (~2x108 m/sec)  propagation delay = d/s A B propagation transmission nodal processing queueing Note: s and R are very different quantities!
  • 46. Introduction 1-46 Caravan analogy  cars “propagate” at 100 km/hr  toll booth takes 12 sec to service car (transmission time)  car~bit; caravan ~ packet  Q: How long until caravan is lined up before 2nd toll booth?  Time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec  Time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr)= 1 hr  A: 62 minutes toll booth toll booth ten-car caravan 100 km 100 km
  • 47. Introduction 1-47 Caravan analogy (more)  Cars now “propagate” at 1000 km/hr  Toll booth now takes 1 min to service a car  Q: Will cars arrive to 2nd booth before all cars serviced at 1st booth?  Yes! After 7 min, 1st car at 2nd booth and 3 cars still at 1st booth.  1st bit of packet can arrive at 2nd router before packet is fully transmitted at 1st router!  See Ethernet applet at AWL Web site toll booth toll booth ten-car caravan 100 km 100 km
  • 48. Introduction 1-48 Nodal delay  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 prop trans queue proc nodal d d d d d    
  • 49. Introduction 1-49 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!
  • 50. Introduction 1-50 “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
  • 51. Introduction 1-51 “Real” Internet delays and routes 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms traceroute: gaia.cs.umass.edu to www.eurecom.fr Three delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu * means no response (probe lost, router not replying) trans-oceanic link
  • 52. Introduction 1-52 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 A B packet being transmitted packet arriving to full buffer is lost buffer (waiting area)
  • 53. Introduction 1-53 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 server, with file of F bits to send to client link capacity Rs bits/sec link capacity Rc bits/sec pipe that can carry fluid at rate Rs bits/sec) pipe that can carry fluid at rate Rc bits/sec) server sends bits (fluid) into pipe
  • 54. Introduction 1-54 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 link on end-end path that constrains end-end throughput bottleneck link
  • 55. Introduction 1-55 Throughput: Internet scenario 10 connections (fairly) share backbone bottleneck link R bits/sec Rs Rs Rs Rc Rc Rc R  per-connection end-end throughput: min(Rc,Rs,R/10)  in practice: Rc or Rs is often bottleneck
  • 56. Introduction 1-56 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
  • 57. Introduction 1-57 Protocol “Layers” Networks are complex!  many “pieces”:  hosts  routers  links of various media  applications  protocols  hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks?
  • 58. Introduction 1-58 Organization of air travel  a series of steps ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing airplane routing
  • 59. Introduction 1-59 ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers airplane routing airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing ticket baggage gate takeoff/landing airplane routing Layering of airline functionality Layers: each layer implements a service  via its own internal-layer actions  relying on services provided by layer below
  • 60. Introduction 1-60 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?
  • 61. Introduction 1-61 Internet protocol stack  application: supporting network applications  FTP, SMTP, HTTP  transport: process-process data transfer  TCP, UDP  network: routing of datagrams from source to destination  IP, routing protocols  link: data transfer between neighboring network elements  PPP, Ethernet  physical: bits “on the wire” application transport network link physical
  • 62. Introduction 1-62 ISO/OSI reference model  presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine- specific conventions  session: synchronization, checkpointing, recovery of data exchange  Internet stack “missing” these layers!  these services, if needed, must be implemented in application  needed? application presentation session transport network link physical
  • 63. Introduction 1-63 source application transport network link physical Ht Hn M segment Ht datagram destination application transport network link physical Ht Hn Hl M Ht Hn M Ht M M network link physical link physical Ht Hn Hl M Ht Hn M Ht Hn M Ht Hn Hl M router switch Encapsulation message M Ht M Hn frame
  • 64. Introduction 1-64 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
  • 65. Introduction 1-65 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!
  • 66. Introduction 1-66 Bad guys can put malware into hosts 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
  • 67. Introduction 1-67 Bad guys can put malware into hosts via Internet  Trojan horse  Hidden part of some otherwise useful software  Today often on a Web page (Active-X, plugin)  Virus  infection by receiving object (e.g., e-mail attachment), actively executing  self-replicating: propagate itself to other hosts, users  Worm:  infection by passively receiving object that gets itself executed  self- replicating: propagates to other hosts, users Sapphire Worm: aggregate scans/sec in first 5 minutes of outbreak (CAIDA, UWisc data)
  • 68. Introduction 1-68 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 traffic 1. select target 2. break into hosts around the network (see botnet) 3. send packets toward target from compromised hosts target
  • 69. Introduction 1-69 The bad guys can sniff packets Packet sniffing:  broadcast media (shared Ethernet, wireless)  promiscuous network interface reads/records all packets (e.g., including passwords!) passing by A B C src:B dest:A payload  Wireshark software used for end-of-chapter labs is a (free) packet-sniffer
  • 70. Introduction 1-70 The bad guys can use false source addresses  IP spoofing: send packet with false source address A B C src:B dest:A payload
  • 71. Introduction 1-71 The bad guys can record and playback  record-and-playback: sniff sensitive info (e.g., password), and use later  password holder is that user from system point of view A B C src:B dest:A user: B; password: foo
  • 72. Introduction 1-72 Network Security  more throughout this course  chapter 8: focus on security  crypographic techniques: obvious uses and not so obvious uses
  • 73. Introduction 1-73 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
  • 74. Introduction 1-74 Internet History  1961: Kleinrock - queueing theory shows effectiveness of packet- switching  1964: Baran - packet- switching in military nets  1967: ARPAnet conceived by Advanced Research Projects Agency  1969: first ARPAnet node operational  1972:  ARPAnet public demonstration  NCP (Network Control Protocol) first host-host protocol  first e-mail program  ARPAnet has 15 nodes 1961-1972: Early packet-switching principles
  • 75. Introduction 1-75 Internet History  1970: ALOHAnet satellite network in Hawaii  1974: Cerf and Kahn - architecture for interconnecting networks  1976: Ethernet at Xerox PARC  ate70’s: proprietary architectures: DECnet, SNA, XNA  late 70’s: switching fixed length packets (ATM precursor)  1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles:  minimalism, autonomy - no internal changes required to interconnect networks  best effort service model  stateless routers  decentralized control define today’s Internet architecture 1972-1980: Internetworking, new and proprietary nets
  • 76. Introduction 1-76 Internet History  1983: deployment of TCP/IP  1982: smtp e-mail protocol defined  1983: DNS defined for name-to-IP- address translation  1985: ftp protocol defined  1988: TCP congestion control  new national networks: Csnet, BITnet, NSFnet, Minitel  100,000 hosts connected to confederation of networks 1980-1990: new protocols, a proliferation of networks
  • 77. Introduction 1-77 Internet History  Early 1990’s: ARPAnet decommissioned  1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)  early 1990s: Web  hypertext [Bush 1945, Nelson 1960’s]  HTML, HTTP: Berners-Lee  1994: Mosaic, later Netscape  late 1990’s: commercialization of the Web Late 1990’s – 2000’s:  more killer apps: instant messaging, P2P file sharing  network security to forefront  est. 50 million host, 100 million+ users  backbone links running at Gbps 1990, 2000’s: commercialization, the Web, new apps
  • 78. Introduction 1-78 Internet History 2007:  ~500 million hosts  Voice, Video over IP  P2P applications: BitTorrent (file sharing) Skype (VoIP), PPLive (video)  more applications: YouTube, gaming  wireless, mobility
  • 79. Introduction 1-79 Introduction: Summary Covered a “ton” of material!  Internet overview  what’s a protocol?  network edge, core, access network  packet-switching versus circuit-switching  Internet structure  performance: loss, delay, throughput  layering, service models  security  history You now have:  context, overview, “feel” of networking  more depth, detail to follow!