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Hasam Panezai

This document discusses the introduction chapter of a computer networking textbook. It provides an overview of what the Internet is, including its basic components and how data is transmitted. It also explains what protocols are and how they are used to govern communication between devices on the Internet.

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Chapter 1 Introduction A 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, 4th edition. that you mention their source (after all, we’d like people to use our book!) Jim Kurose, Keith Ross Addison-Wesley, July  If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. 2012. Thanks and enjoy! JFK/KWR J.F Kurose and K.W. Ross, All Rights Reserved Introduction 1-1
Chapter 1: Introduction Our 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
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
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  routers: forward router packets (chunks of data) Introduction 1-4
“Cool” internet appliances Web-enabled toaster + weather forecaster IP picture frame http://www.ceiva.com/ World’s smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.html Internet phones Introduction 1-5
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
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
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
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
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
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
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
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
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 1-14
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 1-15
Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html Introduction 1-16
Cable Network Architecture: Overview Typically 500 to 5,000 homes cable headend home cable distribution network (simplified) Introduction 1-17
Cable Network Architecture: Overview server(s) cable headend home cable distribution network Introduction 1-18
Cable Network Architecture: Overview cable headend home cable distribution network (simplified) Introduction 1-19
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 1-20
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 1-21
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 1-22
Home networks Typical 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 1-23
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 1-24
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., 10’s-  legacy Ethernet 100’s Gps)  broadband:  low error rate: repeaters  multiple channels on spaced far apart ; immune cable to electromagnetic noise  HFC Introduction 1-25
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 1-26
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 1-27
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 1-28
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 1-29
Network Core: Circuit Switching network 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 1-30
Circuit Switching: FDM and TDM Example: FDM 4 users frequency time TDM frequency time Introduction 1-31
Numerical example  How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network?  All links are 1.536 Mbps  Each link uses TDM with 24 slots/sec  500 msec to establish end-to-end circuit Let’s work it out! Introduction 1-32
Network Core: Packet Switching each 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 time Bandwidth division into “pieces”  Node receives complete Dedicated allocation packet before forwarding Resource reservation Introduction 1-33
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 E 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. Introduction 1-34
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 1-35
Packet switching versus circuit switching Packet 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 1-36
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 (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 providers Tier 1 ISP interconnect (peer) privately Tier 1 ISP Tier 1 ISP Introduction 1-38
Tier-1 ISP: e.g., Sprint POP: point-of-presence to/from backbone peering … … . … … … to/from customers 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-2 ISPs Tier-2 ISP pays Tier-2 ISP also peer Tier-2 ISP privately with tier-1 ISP for connectivity to Tier 1 ISP each other. rest of Internet  tier-2 ISP is customer of tier-1 provider Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Introduction 1-40
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 ISP Local and tier- Tier-2 ISP Tier-2 ISP 3 ISPs are customers of Tier 1 ISP higher tier ISPs connecting them to rest Tier 1 ISP Tier 1 ISP Tier-2 ISP of Internet local Tier-2 ISP Tier-2 ISP ISP local local local ISP ISP ISP Introduction 1-41
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 1-42
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 packet being transmitted (delay) A B 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:  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 1-45
Delay in packet-switched networks 3. 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! transmission A propagation B nodal processing queueing Introduction 1-46
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 1-47
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 1-48
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 1-49
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 traceroute: gaia.cs.umass.edu to www.eurecom.fr Three delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu 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 trans-oceanic 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 link 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 * * * * means no response (probe lost, router not replying) 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms 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 buffer (waiting area) packet being transmitted A B packet arriving to full buffer is lost 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 link capacity server 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 1-54
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 bottleneck link link on end-end path that constrains end-end throughput Introduction 1-55
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 1-56
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 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 1-58
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 1-59
Layering of airline functionality ticket (purchase) ticket (complain) ticket baggage (check) baggage (claim baggage gates (load) gates (unload) gate runway (takeoff) runway (land) takeoff/landing airplane routing airplane routing airplane routing airplane routing airplane routing departure intermediate air-traffic arrival airport control centers airport 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 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 1-62
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 1-63
message M source application Encapsulation segment Ht M transport datagram Hn Ht M network frame 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 network Hl Hn Ht M link router physical 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  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 1-68
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 target compromised hosts 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 C src:B dest:A payload B  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 C src:B dest:A payload B 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 C A src:B dest:A user: B; password: foo B 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 1961-1972: 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 1-75
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 1-76
Internet History 1980-1990: 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 1-77
Internet History 1990, 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 1-78
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! 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 1-80

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Lecture 1 4

  • 1. Chapter 1 Introduction A 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, 4th edition. that you mention their source (after all, we’d like people to use our book!) Jim Kurose, Keith Ross Addison-Wesley, July  If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. 2012. Thanks and enjoy! JFK/KWR J.F Kurose and K.W. Ross, All Rights Reserved Introduction 1-1
  • 2. Chapter 1: Introduction Our 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. 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. 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  routers: forward router packets (chunks of data) Introduction 1-4
  • 5. “Cool” internet appliances Web-enabled toaster + weather forecaster IP picture frame http://www.ceiva.com/ World’s smallest web server http://www-ccs.cs.umass.edu/~shri/iPic.html Internet phones Introduction 1-5
  • 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. 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. 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. 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. 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. 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. 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. 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. 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 1-14
  • 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 1-15
  • 16. Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html Introduction 1-16
  • 17. Cable Network Architecture: Overview Typically 500 to 5,000 homes cable headend home cable distribution network (simplified) Introduction 1-17
  • 18. Cable Network Architecture: Overview server(s) cable headend home cable distribution network Introduction 1-18
  • 19. Cable Network Architecture: Overview cable headend home cable distribution network (simplified) Introduction 1-19
  • 20. 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 1-20
  • 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 1-21
  • 22. 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 1-22
  • 23. Home networks Typical 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 1-23
  • 24. 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 1-24
  • 25. 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., 10’s-  legacy Ethernet 100’s Gps)  broadband:  low error rate: repeaters  multiple channels on spaced far apart ; immune cable to electromagnetic noise  HFC Introduction 1-25
  • 26. 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 1-26
  • 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 1-27
  • 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 1-28
  • 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 1-29
  • 30. Network Core: Circuit Switching network 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 1-30
  • 31. Circuit Switching: FDM and TDM Example: FDM 4 users frequency time TDM frequency time Introduction 1-31
  • 32. Numerical example  How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network?  All links are 1.536 Mbps  Each link uses TDM with 24 slots/sec  500 msec to establish end-to-end circuit Let’s work it out! Introduction 1-32
  • 33. Network Core: Packet Switching each 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 time Bandwidth division into “pieces”  Node receives complete Dedicated allocation packet before forwarding Resource reservation Introduction 1-33
  • 34. 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 E 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. Introduction 1-34
  • 35. 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 1-35
  • 36. Packet switching versus circuit switching Packet 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 1-36
  • 37. 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 (circuit switching) versus on-demand allocation (packet-switching)? Introduction 1-37
  • 38. 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 1-38
  • 39. Tier-1 ISP: e.g., Sprint POP: point-of-presence to/from backbone peering … … . … … … to/from customers Introduction 1-39
  • 40. 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 ISPs Tier-2 ISP pays Tier-2 ISP also peer Tier-2 ISP privately with tier-1 ISP for connectivity to Tier 1 ISP each other. rest of Internet  tier-2 ISP is customer of tier-1 provider Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Introduction 1-40
  • 41. 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 ISP Local and tier- Tier-2 ISP Tier-2 ISP 3 ISPs are customers of Tier 1 ISP higher tier ISPs connecting them to rest Tier 1 ISP Tier 1 ISP Tier-2 ISP of Internet local Tier-2 ISP Tier-2 ISP ISP local local local ISP ISP ISP Introduction 1-41
  • 42. 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 1-42
  • 43. 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
  • 44. 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 1-44
  • 45. 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 1-45
  • 46. Delay in packet-switched networks 3. 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! transmission A propagation B nodal processing queueing Introduction 1-46
  • 47. 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 1-47
  • 48. 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 1-48
  • 49. 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 1-49
  • 50. 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
  • 51. “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
  • 52. “Real” Internet delays and routes traceroute: gaia.cs.umass.edu to www.eurecom.fr Three delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu 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 trans-oceanic 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 link 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 * * * * means no response (probe lost, router not replying) 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms Introduction 1-52
  • 53. 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 1-53
  • 54. 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 capacity server 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 1-54
  • 55. 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 link link on end-end path that constrains end-end throughput Introduction 1-55
  • 56. 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 1-56
  • 57. 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
  • 58. 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 1-58
  • 59. 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 1-59
  • 60. Layering of airline functionality ticket (purchase) ticket (complain) ticket baggage (check) baggage (claim baggage gates (load) gates (unload) gate runway (takeoff) runway (land) takeoff/landing airplane routing airplane routing airplane routing airplane routing airplane routing departure intermediate air-traffic arrival airport control centers airport Layers: each layer implements a service  via its own internal-layer actions  relying on services provided by layer below Introduction 1-60
  • 61. 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
  • 62. 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 1-62
  • 63. 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 1-63
  • 64. message M source application Encapsulation segment Ht M transport datagram Hn Ht M network frame 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 network Hl Hn Ht M link router physical Introduction 1-64
  • 65. 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
  • 66. 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
  • 67. 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
  • 68. Bad guys can put malware into hosts 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 1-68
  • 69. 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 target compromised hosts Introduction 1-69
  • 70. 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 C src:B dest:A payload B  Wireshark software used for end-of-chapter labs is a (free) packet-sniffer Introduction 1-70
  • 71. The bad guys can use false source addresses  IP spoofing: send packet with false source address A C src:B dest:A payload B Introduction 1-71
  • 72. 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 C A src:B dest:A user: B; password: foo B Introduction 1-72
  • 73. Network Security  more throughout this course  chapter 8: focus on security  crypographic techniques: obvious uses and not so obvious uses Introduction 1-73
  • 74. 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
  • 75. Internet History 1961-1972: 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 1-75
  • 76. 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 1-76
  • 77. Internet History 1980-1990: 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 1-77
  • 78. Internet History 1990, 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 1-78
  • 79. 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
  • 80. Introduction: Summary Covered 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 1-80

Editor's Notes

  • #32: 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