1. 1: Introduction 1 Part I: Introduction Our goal: r get context, overview, “feel” of networking r more depth, detail later in course r approach: m descriptive m use Internet as example Overview: r what’s the Internet r what’s a protocol? r network edge r network core r access net, physical media r performance: loss, delay r protocol layers, service models r backbones, NAPs, ISPs r history Assignment: read chapter 1 in text

2. 1: Introduction 2 What’s the Internet: “nuts and bolts” view r millions of connected computing devices: hosts, end-systems m pc’s workstations, servers m PDA’s phones, toasters running network apps r communication links m fiber, copper, radio, satellite r routers: forward packets (chunks) of data thru network local ISP company network regional ISP router workstation server mobile

3. 1: Introduction 3 “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 http://dancing-man.com/robin/toasty/

4. 1: Introduction 4 What’s the Internet: “nuts and bolts” view r protocols: control sending, receiving of msgs m e.g., TCP, IP, HTTP, FTP, PPP r Internet: “network of networks” m loosely hierarchical m public Internet versus private intranet r Internet standards m RFC: Request for comments m IETF: Internet Engineering Task Force local ISP company network regional ISP router workstation server mobile

5. 1: Introduction 5 What’s the Internet: a service view r communication infrastructure enables distributed applications: m WWW, email, games, e- commerce, database., voting, file (MP3) sharing r communication services provided: m connectionless m connection-oriented r cyberspace [Gibson]: “a consensual hallucination experienced daily by billions of operators, in every nation,...."

6. 1: Introduction 6 What’s a protocol? human protocols: r “what’s the time?” r “I have a question” r introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: r machines rather than humans r 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

7. 1: Introduction 7 What’s a protocol? a human protocol and a computer network protocol: Q: Other human protocol? Hi Got the time? 2:00 TCP connection req. TCP connection reply. Get http://gaia.cs.umass.edu/index.htm time

8. 1: Introduction 8 A closer look at network structure: r network edge: applications and hosts r network core: m routers m network of networks r access networks, physical media: communication links

9. 1: Introduction 9 The network edge: r end systems (hosts): m run application programs m e.g., WWW, email m at “edge of network” r client/server model m client host requests, receives service from server m e.g., WWW client (browser)/ server; email client/server r peer-peer model: m host interaction symmetric m e.g.: Gnutella, KaZaA

10. 1: Introduction 10 Network edge: connection-oriented service Goal: data transfer between end sys. r handshaking: setup (prepare for) data transfer ahead of time m Hello, hello back human protocol m set up “state” in two communicating hosts r TCP - Transmission Control Protocol m Internet’s connection- oriented service TCP service [RFC 793] r reliable, in-order byte- stream data transfer m loss: acknowledgements and retransmissions r flow control: m sender won’t overwhelm receiver r congestion control: m senders “slow down sending rate” when network congested

11. 1: Introduction 11 Network edge: connectionless service Goal: data transfer between end systems m same as before! r UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service m unreliable data transfer m no flow control m no congestion control App’s using TCP: r HTTP (WWW), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP: r streaming media, teleconferencing, Internet telephony

12. 1: Introduction 12 The Network Core r mesh of interconnected routers r 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”

13. 1: Introduction 13 Network Core: Circuit Switching End-end resources reserved for “call” r link bandwidth, switch capacity r dedicated resources: no sharing r circuit-like (guaranteed) performance r call setup required

14. 1: Introduction 14 Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces” r pieces allocated to calls r resource piece idle if not used by owning call (no sharing) r dividing link bandwidth into “pieces” m frequency division m time division

15. 1: Introduction 15 Circuit Switching: TDMA and TDMA FDMA frequency time TDMA frequency time 4 users Example:

16. 1: Introduction 16 Network Core: Packet Switching each end-end data stream divided into packets r user A, B packets share network resources r each packet uses full link bandwidth r resources used as needed, resource contention: r aggregate resource demand can exceed amount available r congestion: packets queue, wait for link use r store and forward: packets move one hop at a time m transmit over link m wait turn at next link Bandwidth division into “pieces” Dedicated allocation Resource reservation

17. 1: Introduction 17 Network Core: Packet Switching Packet-switching versus circuit switching: human restaurant analogy r other human analogies? A B C 10 Mbs Ethernet 1.5 Mbs 45 Mbs D E statistical multiplexing queue of packets waiting for output link

18. 1: Introduction 18 Network Core: Packet Switching Packet-switching: store and forward behavior r break message into smaller chunks: “packets” r Store-and-forward: switch waits until chunk has completely arrived, then forwards/routes r Q: what if message was sent as single unit?

19. 1: Introduction 19 Packet switching versus circuit switching r 1 Mbit link r each user: m 100Kbps when “active” m active 10% of time r circuit-switching: m 10 users r packet switching: m with 35 users, probability > 10 active less than.0004 Packet switching allows more users to use network! N users 1 Mbps link

20. 1: Introduction 20 Packet switching versus circuit switching r Great for bursty data m resource sharing m no call setup r Excessive congestion: packet delay and loss m protocols needed for reliable data transfer, congestion control r Q: How to provide circuit-like behavior? m bandwidth guarantees needed for audio/video apps m still an unsolved problem (chapter 6) Is packet switching a “slam dunk winner?”

21. 1: Introduction 21 Packet-switched networks: routing r Goal: move packets among routers from source to destination m we’ll study several path selection algorithms (chapter 4) r datagram network (example IP): m destination address determines next hop m routes may change during session m analogy: driving, asking directions r virtual circuit network (example ATM): m each packet carries tag (virtual circuit ID), tag determines next hop m fixed path determined at call setup time, remains fixed thru call m routers maintain per-call state

22. 1: Introduction 22 Access networks and physical media Q: How to connect end systems to edge router? r residential access nets r institutional access networks (school, company) r mobile access networks Keep in mind: r bandwidth (bits per second) of access network? r shared or dedicated?

23. 1: Introduction 23 Residential access: point to point access r Dialup via modem m up to 56Kbps direct access to router (conceptually) r ISDN: integrated services digital network: 128Kbps all- digital connect to router r ADSL: asymmetric digital subscriber line m up to 1 Mbps home-to-router m up to 8 Mbps router-to-home m ADSL deployment: happening

24. 1: Introduction 24 Residential access: cable modems r HFC: hybrid fiber coax m asymmetric: up to 10Mbps upstream, 1 Mbps downstream r network of cable and fiber attaches homes to ISP router m shared access to router among home m issues: congestion, dimensioning r deployment: available via cable companies, e.g., MediaOne

25. 1: Introduction 25 Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

26. 1: Introduction 26 Institutional access: local area networks r company/univ local area network (LAN) connects end system to edge router r Ethernet: m shared or dedicated cable connects end system and router m 10 Mbs, 100Mbps, Gigabit Ethernet r deployment: institutions, home LANs happening now r LANs: chapter 5

27. 1: Introduction 27 Wireless access networks r shared wireless access network connects end system to router r wireless LANs: m radio spectrum replaces wire m e.g., Lucent Wavelan 11 Mbps r wider-area wireless access m CDPD: wireless access to ISP router via cellular network base station mobile hosts router

28. 1: Introduction 28 Home networks Typical home network components: r ADSL or cable modem r router/firewall r Ethernet r wireless access point wireless access point wireless laptops router/ firewall cable modem to/from cable headend Ethernet (switched)

29. 1: Introduction 29 Physical Media r physical link: transmitted data bit propagates across link r guided media: m signals propagate in solid media: copper, fiber r unguided media: m signals propagate freely, e.g., radio Twisted Pair (TP) r two insulated copper wires m Category 3: traditional phone wires, 10 Mbps Ethernet m Category 5 TP: 100Mbps Ethernet

30. 1: Introduction 30 Physical Media: coax, fiber Coaxial cable: r wire (signal carrier) within a wire (shield) m baseband: single channel on cable m broadband: multiple channel on cable r bidirectional r common use in 10Mbs Ethernet Fiber optic cable: r glass fiber carrying light pulses r high-speed operation: m 100Mbps Ethernet m high-speed point-to-point transmission (e.g., 5 Gps) r low error rate

31. 1: Introduction 31 Physical media: radio r signal carried in electromagnetic spectrum r no physical “wire” r bidirectional r propagation environment effects: m reflection m obstruction by objects m interference Radio link types: r microwave m e.g. up to 45 Mbps channels r LAN (e.g., WaveLAN) m 2Mbps, 11Mbps r wide-area (e.g., cellular) m e.g. CDPD, 10’s Kbps r satellite m up to 50Mbps channel (or multiple smaller channels) m 270 Msec end-end delay m geosynchronous versus LEOS

32. 1: Introduction 32 Delay in packet-switched networks packets experience delay on end-to-end path r four sources of delay at each hop r nodal processing: m check bit errors m determine output link r queueing m time waiting at output link for transmission m depends on congestion level of router A B propagation transmission nodal processing queueing

33. 1: Introduction 33 Delay in packet-switched networks Transmission delay: r R=link bandwidth (bps) r L=packet length (bits) r time to send bits into link = L/R Propagation delay: r d = length of physical link r s = propagation speed in medium (~2x10 8 m/sec) r propagation delay = d/s A B propagation transmission nodal processing queueing Note: s and R are very different quantities!

34. 1: Introduction 34 Queueing delay (revisited) r R=link bandwidth (bps) r L=packet length (bits) r a=average packet arrival rate traffic intensity = La/R r La/R ~ 0: average queueing delay small r La/R -> 1: delays become large r La/R > 1: more “work” arriving than can be serviced, average delay infinite!

35. 1: Introduction 35 “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: routers, rt delays on source-dest path also: pingplotter, various windows programs

36. 1: Introduction 36 Protocol “Layers” Networks are complex! r 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?

37. 1: Introduction 37 Organization of air travel r a series of steps ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing

38. 1: Introduction 38 Organization of air travel : a different view Layers: each layer implements a service m via its own internal-layer actions m relying on services provided by layer below ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing

39. 1: Introduction 39 Layered air travel: services Counter-to-counter delivery of person+bags baggage-claim-to-baggage-claim delivery people transfer: loading gate to arrival gate runway-to-runway delivery of plane airplane routing from source to destination

40. 1: Introduction 40 Distributed implementation of layer functionality ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing Departing airport arriving airport intermediate air traffic sites airplane routing

41. 1: Introduction 41 Why layering? Dealing with complex systems: r explicit structure allows identification, relationship of complex system’s pieces m layered reference model for discussion r 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 r layering considered harmful?

42. 1: Introduction 42 Internet protocol stack r application: supporting network applications m ftp, smtp, http r transport: host-host data transfer m tcp, udp r network: routing of datagrams from source to destination m ip, routing protocols r link: data transfer between neighboring network elements m ppp, ethernet r physical: bits “on the wire” application transport network link physical

43. 1: Introduction 43 Layering: logical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical Each layer: r distributed r “entities” implement layer functions at each node r entities perform actions, exchange messages with peers

44. 1: Introduction 44 Layering: logical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data E.g.: transport r take data from app r add addressing, reliability check info to form “datagram” r send datagram to peer r wait for peer to ack receipt r analogy: post office data transport ack

45. 1: Introduction 45 Layering: physical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data

46. 1: Introduction 46 Protocol layering and data Each layer takes data from above r adds header information to create new data unit r passes new data unit to layer below application transport network link physical application transport network link physical source destination M M M M H t H t H n H t H n H l M M M M H t H t H n H t H n H l message segment datagram frame

47. 1: Introduction 47 Internet structure: network of networks r roughly hierarchical r national/international backbone providers (NBPs) m e.g. BBN/GTE, Sprint, AT&T, IBM, UUNet m interconnect (peer) with each other privately, or at public Network Access Point (NAPs) r regional ISPs m connect into NBPs r local ISP, company m connect into regional ISPs NBP A NBP B NAP regional ISP local ISP local ISP

48. 1: Introduction 48 National Backbone Provider e.g. Sprint US backbone network

49. 1: Introduction 49 Internet History r 1961: Kleinrock - queueing theory shows effectiveness of packet- switching r 1964: Baran - packet- switching in military nets r 1967: ARPAnet conceived by Advanced Research Projects Agency r 1969: first ARPAnet node operational r 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

50. 1: Introduction 50 Internet History r 1970: ALOHAnet satellite network in Hawaii r 1973: Metcalfe’s PhD thesis proposes Ethernet r 1974: Cerf and Kahn - architecture for interconnecting networks r late70’s: proprietary architectures: DECnet, SNA, XNA r late 70’s: switching fixed length packets (ATM precursor) r 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

51. 1: Introduction 51 Internet History r 1983: deployment of TCP/IP r 1982: smtp e-mail protocol defined r 1983: DNS defined for name-to-IP- address translation r 1985: ftp protocol defined r 1988: TCP congestion control r new national networks: Csnet, BITnet, NSFnet, Minitel r 100,000 hosts connected to confederation of networks 1980-1990: new protocols, a proliferation of networks

52. 1: Introduction 52 Internet History r Early 1990’s: ARPAnet decommissioned r 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) r early 1990s: WWW m hypertext [Bush 1945, Nelson 1960’s] m HTML, http: Berners-Lee m 1994: Mosaic, later Netscape m late 1990’s: commercialization of the WWW Late 1990’s: r est. 50 million computers on Internet r est. 100 million+ users r backbone links running at 1 Gbps 1990’s: commercialization, the WWW

53. 1: Introduction 53 Introduction: Summary Covered a “ton” of material! r Internet overview r what’s a protocol? r network edge, core, access network m packet-switching versus circuit-switching r performance: loss, delay r layering and service models r backbones, NAPs, ISPs r history You now have: r context, overview, “feel” of networking r more depth, detail later in course