1. Introduction1-1 How does the Internet Work Computer Networking: A Top Down Approach Featuring the Internet, 3 rd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2004. 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 represent a lot of work on our part. In return for use, we only ask the following:  If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!)  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. Thanks and enjoy! JFK/KWR All material copyright 1996-2004 J.F Kurose and K.W. Ross, All Rights Reserved

2. Introduction1-2 Chapter 1: Introduction Our goal:  get “feel” and terminology Overview:  what’s the Internet  what’s a protocol?  network edge  network core  access net, physical media  Internet/ISP structure  protocol layers, service models  History

3. Introduction1-3 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History

4. Introduction1-4 What’s the Internet: “nuts and bolts” view  millions of connected computing devices: hosts = end systems  running network apps  communication links m fiber, copper, radio, satellite m transmission rate = bandwidth, capacity  routers: forward packets (chunks of data) local ISP company network regional ISP router workstation server mobile

5. Introduction1-5 What’s the Internet: “nuts and bolts” view  protocols control sending, receiving of msgs m e.g., TCP, IP, HTTP, FTP, PPP  Internet: “network of networks” m loosely hierarchical m public Internet versus private intranet  Internet standards m RFC: Request for comments m IETF: Internet Engineering Task Force local ISP company network regional ISP router workstation server mobile

6. Introduction1-6 What’s the Internet: a service view  communication infrastructure enables distributed applications: m Web, email, games, e- commerce, file sharing  communication services provided to apps: m Connectionless unreliable m connection-oriented reliable

7. Introduction1-7 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

8. Introduction1-8 What’s a protocol? a human protocol and a computer network protocol: Q: Other human protocols? Assalam o alaikum Walaikum Salam Got the time? 2:00 TCP connection req TCP connection response Get http://www.awl.com/kurose-ross time

9. Introduction1-9 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History

10. Introduction1-10 A closer look at network structure:  network edge: applications and hosts  network core: m routers m network of networks  access networks, physical media: communication links

11. Introduction1-11 The network edge:  end systems (hosts): m run application programs m e.g. Web, email m at “edge of network”  client/server model m client host requests, receives service from always-on server m e.g. Web browser/server; email client/server  peer-peer model: m minimal (or no) use of dedicated servers m e.g. Gnutella, KaZaA

12. Introduction1-12 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History

13. Introduction1-13 The Network Core  mesh of interconnected routers  the fundamental question: how is data transferred through net? m circuit switching: dedicated circuit per call: telephone net m packet-switching: data sent thru net in discrete “chunks”

14. Introduction1-14 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

15. Introduction1-15 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)

16. Introduction1-16 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 m Node receives complete packet before forwarding Bandwidth division into “pieces” Dedicated allocation Resource reservation

17. Introduction1-17 Packet Switching: Statistical Multiplexing Sequence of A & B packets does not have fixed pattern  statistical multiplexing. A B C 10 Mb/s Ethernet 1.5 Mb/s D E statistical multiplexing queue of packets waiting for output link

18. Introduction1-18 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History

19. Introduction1-19 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?

20. Introduction1-20 Residential access: point to point access  Dialup via modem m up to 56Kbps direct access to router (often less) m Can’t surf and phone at same time: can’t be “always on”  ADSL: asymmetric digital subscriber line m up to 1 Mbps upstream (today typically < 256 kbps) m up to 8 Mbps downstream (today typically < 1 Mbps) m FDM: 50 kHz - 1 MHz for downstream 4 kHz - 50 kHz for upstream 0 kHz - 4 kHz for ordinary telephone

21. Introduction1-21 Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

22. Introduction1-22 Cable Network Architecture: Overview home cable headend cable distribution network (simplified) Typically 500 to 5,000 homes

23. Introduction1-23 Cable Network Architecture: Overview home cable headend cable distribution network (simplified)

24. Introduction1-24 Cable Network Architecture: Overview home cable headend cable distribution network server(s)

25. Introduction1-25 Company access: local area networks  company/univ local area network (LAN) connects end system to edge router  Ethernet: m shared or dedicated link connects end system and router m 10 Mbs, 100Mbps, Gigabit Ethernet

26. Introduction1-26 Wireless access networks  shared wireless access network connects end system to router m via base station aka “access point”  wireless LANs: m 802.11b (WiFi): 11 Mbps  wider-area wireless access m provided by telco operator m 3G ~ 384 kbps Will it happen?? m WAP/GPRS in Europe base station mobile hosts router

27. Introduction1-27 Home networks Typical home network components:  ADSL or cable modem  router/firewall/NAT  Ethernet  wireless access point wireless access point wireless laptops router/ firewall cable modem to/from cable headend Ethernet

28. Introduction1-28 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History

29. Introduction1-29 Internet structure: network of networks  roughly hierarchical  at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity, Sprint, AT&T), national/international coverage m treat each other as equals Tier 1 ISP Tier-1 providers interconnect (peer) privately NAP Tier-1 providers also interconnect at public network access points (NAPs)

30. Introduction1-30 Internet structure: network of networks  “Tier-2” ISPs: smaller (often regional) ISPs m Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier 1 ISP NAP 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, interconnect at NAP

31. Introduction1-31 Internet structure: network of networks  “Tier-3” ISPs and local ISPs m last hop (“access”) network (closest to end systems) Tier 1 ISP NAP 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

32. Introduction1-32 Internet structure: network of networks  a packet passes through many networks! Tier 1 ISP NAP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP

33. Introduction1-33

34. Introduction1-34 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History

35. Introduction1-35 Protocol “Layers” Networks are complex!  many “pieces”: m hosts m routers m links of various media m applications m protocols m hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks?

36. Introduction1-36 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

37. Introduction1-37 ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers 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 m via its own internal-layer actions m relying on services provided by layer below

38. Introduction1-38 Why layering? Dealing with complex systems:  explicit structure allows identification, relationship of complex system’s pieces m layered reference model for discussion  modularization eases maintenance, updating of system m change of implementation of layer’s service transparent to rest of system m e.g., change in gate procedure doesn’t affect rest of system  layering considered harmful?

39. Introduction1-39 Internet protocol stack  application: supporting network applications m FTP, SMTP, STTP  transport: host-host data transfer m TCP, UDP  network: routing of datagrams from source to destination m IP, routing protocols  link: data transfer between neighboring network elements m PPP, Ethernet  physical: bits “on the wire” application transport network link physical

40. Introduction1-40 message segment datagram frame source application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M destination application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M network link physical link physical HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn HlHl M HtHt HnHn HlHl M router switch Encapsulation

41. Introduction1-41 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History

42. Introduction1-42 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: m ARPAnet demonstrated publicly m NCP (Network Control Protocol) first host- host protocol m first e-mail program m ARPAnet has 15 nodes 1961-1972: Early packet-switching principles

43. Introduction1-43 Internet History  1970: ALOHAnet satellite network in Hawaii  1973: Metcalfe’s PhD thesis proposes Ethernet  1974: Cerf and Kahn - architecture for interconnecting networks  late70’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: m minimalism, autonomy - no internal changes required to interconnect networks m best effort service model m stateless routers m decentralized control define today’s Internet architecture 1972-1980: Internetworking, new and proprietary nets

44. Introduction1-44 Internet History  Early 1990’s: ARPAnet decommissioned  1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)  early 1990s: Web m hypertext [Bush 1945, Nelson 1960’s] m HTML, HTTP: Berners-Lee m 1994: Mosaic, later Netscape m 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