1. 1 Electrical Engineering E6761 Computer Communication Networks Professor Dan Rubenstein Tues 4:10-6:40, Mudd 545 Call # 67650 Course URL: http://www.cs.columbia.edu/~danr/EE6761

2. 2 Today r Course Overview / Structure / Handouts r Intro r Socket Programming

3. 3 Overview r Bookmark the course web-page! m http://www.cs.columbia.edu/~danr/EE6761 r Syllabus m Office hours: Mon 3-4? m TA m Mid-term date & time r Survey r HW #0 – due tomorrow - not graded! r PA #1

4. 4 Introduction (Reading: Kurose-Ross Chap 1) 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 r ATM network

5. 5 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

6. 6 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 m see class web-page for pointers to URLs local ISP company network regional ISP router workstation server mobile

7. 7 What’s the Internet: a service view r communication infrastructure enables distributed applications: m WWW, email, games, e- commerce, database, voting, m more? r communication services provided: m connectionless m connection-oriented

8. 8 What’s a network protocol? … specific msgs sent … specific actions taken when msgs received, or other events 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

9. 9 What’s a protocol? a human protocol and a computer network protocol: Hi Got the time? 2:00 TCP connection req. TCP connection reply. Get http://gaia.cs.umass.edu/index.htm time

10. 10 A closer look at network structure: r network edge: applications and hosts r network core: m routers m network of networks r access networks m residential m institutional m mobile r physical media m wire (digital / analog) m wireless (radio / cellular)

11. 11 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.: teleconferencing

12. 12 Network edge: connection-oriented service Goal: data transfer between end sys. r handshaking: setup (prepare for) data transfer ahead of time m set up “state” in two communicating hosts r TCP - Transmission Control Protocol m Internet’s de-facto connection-oriented service TCP service [RFC 793] r reliable, in-order byte- stream data transfer m dealing with loss: acknowledgements and retransmissions r flow control: m sender won’t overwhelm receiver r congestion control: m senders “slow down sending rate” when network congestion detected

13. 13 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

14. 14 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”

15. 15 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

16. 16 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 m code division

17. 17 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

18. 18 Network Core: Packet Switching A B C 10 Mbs Ethernet 1.5 Mbs 45 Mbs D E statistical multiplexing queue of packets waiting for output link

19. 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 that.004 Packet switching allows more users to use network! N users 1 Mbps link

20. 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 still an unsolved problem (chapter 6 of Kurose- Ross) Is packet switching a “slam dunk winner?”

21. 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: m destination address determines next hop m routes may change during session m analogy: driving, asking directions r virtual circuit network: 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. 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 (e.g. cable, ethernet) or dedicated (e.g., DSL)?

23. 23 Residential access: point to point access r Dialup via modem m up to 56Kbps direct access to router (conceptually) r ISDN: intergrated 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

24. 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

25. 25 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 soon r LANs: chapter 5

26. 26 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 10 Mbps r wider-area wireless access m CDPD: wireless access to ISP router via cellular network base station mobile hosts router

27. 27 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

28. 28 Physical Media: coax, fiber Coaxial cable: r wire (signal carrier) within a wire (shield) m baseband: single channel on cable m broadband: multiple channels 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

29. 29 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 (delay v. cost)

30. 30 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

31. 31 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 quantitites!

32. 32 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!

33. 33 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?

34. 34 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?

35. 35 The ISO/OSI protocol stack application presentation session transport network link physical r International Standards Organization’s Open System Interconnection p what did presentation and session layers do?

36. 36 Internet protocol stack r application: supporting network applications m ftp, smtp, http r transport: host-host data transfer m tcp, udp (reliable delivery, rate regulation) r network: routing of datagrams from source to destination m ip, routing protocols r link: data transfer between neighboring network elements m ppp, ethernet, wireless, multiple access protocols r physical: bits “on the wire” application transport network link physical

37. 37 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

38. 38 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

39. 39 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

40. 40 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

41. 41 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

42. 42 National Backbone Provider e.g. BBN/GTE US backbone network

43. 43 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 Reearch 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

44. 44 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

45. 45 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

46. 46 Internet History r Early 1990’s: ARPAnet decomissioned 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 runnning at 1 Gbps 1990’s: commercialization, the WWW

47. 47 ATM: Asynchronous Transfer Mode nets Internet: r today’s de facto standard for global data networking 1980’s: r telco’s develop ATM: competing network standard for carrying high-speed voice/data r standards bodies: m ATM Forum m ITU ATM principles: r small (48 byte payload, 5 byte header) fixed length cells (like packets) m fast switching m small size good for voice r virtual-circuit network: switches maintain state for each “call” r well-defined interface between “network” and “user” (think of telephone company)

48. 48 ATM layers r ATM Adaptation Layer (AAL): interface to upper layers m end-system m segmentation/rea ssembly r ATM Layer: cell switching r Physical AAL ATM physical AAL ATM physical AAL ATM physical AAL ATM physical ATM physical Where’s the application? r ATM: lower layer r functionality only r IP-over ATM: later application TCP/UDP IP application TCP/UDP IP application TCP/UDP IP application TCP/UDP IP

49. 49 Intro: Summary Covered a “ton” of material! r Internet overview r what’s a protocol? r network edge, core, access network r performance: loss, delay r layering and service models r backbones, NAPs, ISPs r history r ATM network You now hopefully have: r context, overview, “feel” of networking r more depth, detail later in course