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CE80N Introduction to Networks & The Internet

CE80N Introduction to Networks & The Internet. Dr. Chane L. Fullmer UCSC Winter 2002. Next Week – Inside the Internet. Jan 22 (T) Inside the Internet Chapter 15, IP: Software to Create a Virtual Network Jan 24 (Th) Inside the Internet Chapter. 16, TCP: Software For Reliable Communication

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CE80N Introduction to Networks & The Internet

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  1. CE80NIntroduction to Networks&The Internet Dr. Chane L. Fullmer UCSC Winter 2002 CE80N -- Winter 2002 -- Lecture #5

  2. Next Week – Inside the Internet • Jan 22 (T) Inside the Internet • Chapter 15, IP: Software to Create a Virtual Network • Jan 24 (Th) Inside the Internet • Chapter. 16, TCP: Software For Reliable Communication • Chapter. 19, Why the Internet Works Well CE80N -- Winter 2002 -- Lecture #5

  3. 1961: Kleinrock - queueing theory shows effectiveness of packet-switching 1964: Baran - packet-switching in military nets 1967: ARPAnet conceived by Advanced Research Projects Agency 1969: first ARPAnet node operational 1972: ARPAnet demonstrated publicly NCP (Network Control Protocol) first host-host protocol first e-mail program ARPAnet has 15 nodes More Internet History 1961-1972: Early packet-switching principles CE80N -- Winter 2002 -- Lecture #5

  4. 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: minimalism, autonomy - no internal changes required to interconnect networks best effort service model stateless routers decentralized control define today’s Internet architecture More Internet History 1972-1980: Internetworking, new and proprietary nets CE80N -- Winter 2002 -- Lecture #5

  5. 1982: smtp e-mail protocol defined 1983: deployment of TCP/IP 1983: DNS defined for name-to-IP-address translation 1985: ftp protocol defined 1988: TCP congestion control new national networks: Csnet, BITnet, NSFnet 100,000 hosts connected to confederation of networks More Internet History 1980-1990: new protocols, a proliferation of networks CE80N -- Winter 2002 -- Lecture #5

  6. Early 1990’s: ARPAnet decommissioned 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) early 1990s: WWW hypertext [Bush 1945, Nelson 1960’s] HTML, http: Berners-Lee 1994: Mosaic, later Netscape late 1990’s: commercialization of the WWW Late 1990’s: est. 50 million computers on Internet est. 100 million+ users backbone links running at 1 Gbps More Internet History 1990’s: commercialization, the WWW CE80N -- Winter 2002 -- Lecture #5

  7. Reading • Chapter 12, Packet Switching • Chapter 13, A Network of Networks • Chapter 14, ISPs and Network Connections CE80N -- Winter 2002 -- Lecture #5

  8. How does a Network work? CE80N -- Winter 2002 -- Lecture #5

  9. How Does the Network work ? • Circuit switching • Network resources reserved and dedicated from sender to receiver (circuit) • Control signaling and data transfers are separated • Control information processing at circuit setup and termination CE80N -- Winter 2002 -- Lecture #5

  10. How Does the Network Work? • Sharing is a good thing.. • Saves money… • One public phone vs. a cell phone for each individual • One central conveyor belt in warehouse • But, costs time… • Waiting for the resource to be free • Long winded conversationalist • Big order on the conveyor belt CE80N -- Winter 2002 -- Lecture #5

  11. How Does the Network Work • Sharing by taking turns… • Conveyor belt model • Allow packages to be interspersed • Individual order’s packages are multiplexed with others onto the moving belt.. • Networks use a similar idea • Packet Switching • Packetize data to transfer • Multiplex it onto the wire CE80N -- Winter 2002 -- Lecture #5

  12. C C C D D D D How Does the Network Work? • Packet Switching Example A C D B CE80N -- Winter 2002 -- Lecture #5

  13. How Does the Network Work? • Packet Switching… • Avoids some delays • Resource is shared by multiplexing packets • Short messages do not have to wait for long ones to complete. • Overhead • Packetizing does not come for free • Header with labeling information is added CE80N -- Winter 2002 -- Lecture #5

  14. How Does a Network Work • Packet Switching… • Labeling (Header information) • Source (sender’s) address • Destination (recipient’s) address • Packet size • Sequence number • Error checking information CE80N -- Winter 2002 -- Lecture #5

  15. How Does a Network Work • Packet Switching… • Computer Addresses Each computer attached to a network is assigned a unique number – called its address. A packet contains the address of the computer that sent it and the address of the computer to which it is sent. CE80N -- Winter 2002 -- Lecture #5

  16. How Does a Network Work? • Packet Switching… • Packet sizes are variable • There is a maximum packet size • Maximum transmission unit (MTU) • No minimum size • But, header size is fixed -- ~40 bytes • Transmission seems fast • 1000+ packets/second on campus LAN CE80N -- Winter 2002 -- Lecture #5

  17. How Does a Network Work • Packet Switching… • Sharing is automatic and fair • Hardware handles the sharing • Adapts as more/less computers are active • Remote devices can be shared • Printers • Must be network “smart” • File Systems CE80N -- Winter 2002 -- Lecture #5

  18. Compare and Contrast • Circuit-Switched • guaranteed transmission • large setup delays • reliable connection • quality-of-service • idle time is wasted • bandwidth granularity problem • Packet-Switched • small setup delays, header overhead • unreliable connection • efficient use of available bandwidth • congestion (queues) result in dropped packets CE80N -- Winter 2002 -- Lecture #5

  19. How Does a Network Work? • Packet Switching and the Internet All data is transferred across the Internet in packets. A sender divides a message, or document, into packets and transfers the packets across the Internet. A receiver reassembles the original message from the packets that arrive. Packets from many machines traverse the Internet at the same time. CE80N -- Winter 2002 -- Lecture #5

  20. 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” The Network Core CE80N -- Winter 2002 -- Lecture #5

  21. End-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required Network Core: Circuit Switching CE80N -- Winter 2002 -- Lecture #5

  22. network resources (e.g., bandwidth) divided into “pieces” pieces allocated to calls resource piece idle if not used by owning call (no sharing) dividing link bandwidth into “pieces” frequency division time division Network Core: Circuit Switching CE80N -- Winter 2002 -- Lecture #5

  23. each end-to-end data stream is divided into packets user packets share network resources each packet uses full link bandwidth resources used as needed Bandwidth division into “pieces” Dedicated allocation Resource reservation Network Core: Packet Switching 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 • transmit over link • wait turn at next link CE80N -- Winter 2002 -- Lecture #5

  24. Packet-switching versus circuit switching: Personal Driving analogy other human analogies? 10 Mbs Ethernet C A statistical multiplexing 1.5 Mbs B queue of packets waiting for output link 45 Mbs D E Network Core: Packet Switching CE80N -- Winter 2002 -- Lecture #5

  25. Network Core: Packet SwitchingStore & Forward Behavior CE80N -- Winter 2002 -- Lecture #5

  26. 1 Mbit link each user: 100Kbps when “active” active 10% of time circuit-switching: 10 users packet switching: with 35 users, probability > 10 active less that .004 Packet switching allows more users to use network! Packet switching versus circuit switching N users 1 Mbps link CE80N -- Winter 2002 -- Lecture #5

  27. Great for bursty data resource sharing 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 Is packet switching a “slam dunk winner?” Packet switching versus circuit switching CE80N -- Winter 2002 -- Lecture #5

  28. Goal: move packets among routers from source to destination we’ll look at a couple of path selection algorithms datagram network: destination address determines next hop routes may change during session analogy: driving, asking directions – without a map! virtual circuit network: each packet carries tag (virtual circuit ID), tag determines next hop fixed path determined at call setup time, remains fixed thru call routers maintain per-call state Packet-switched networks: routing CE80N -- Winter 2002 -- Lecture #5

  29. 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? Access networks and physical media CE80N -- Winter 2002 -- Lecture #5

  30. packets experience delay on end-to-end path four sources of delay at each hop Processing delay: check bit errors determine output link Queueing delay: time waiting at output link for transmission depends on congestion level of router transmission A propagation B nodal processing queueing Delay in packet-switched networks CE80N -- Winter 2002 -- Lecture #5

  31. Transmission delay: R=link bandwidth (bps) L=packet length (bits) time to send bits into link = L/R Propagation delay: d = length of physical link s = propagation speed in medium (~3x108 m/sec) propagation delay = d/s Note: s and R are very different quantities! transmission A propagation B nodal processing queueing Delay in packet-switched networks CE80N -- Winter 2002 -- Lecture #5

  32. R=link bandwidth (bps) L=packet length (bits) l = average packet arrival rate Queueing delay (revisited) traffic intensity = l(L/R) l • l(L/R) ~ 0: average queueing delay small • l(L/R) -> 1: delays become large • l(L/R) > 1: more “work” arriving than can be serviced • average delay approaches infinity! CE80N -- Winter 2002 -- Lecture #5

  33. How Does a Network Work? • Various network technologies are incompatible… • Many tradeoffs – cost, speed, extensibility, etc.. • It is impractical, or infeasible, to require all computers to use the same network technology • Needs of Engineering vs. Administration CE80N -- Winter 2002 -- Lecture #5

  34. How Does a Network Work • Extending a network is simple…. Network Direct Wire Wireless Dial-Up Line POTS Optical Fiber CE80N -- Winter 2002 -- Lecture #5

  35. How Does A Network Work • A computer can have multiple NICs • Each NIC can connect to a separate network Network A Network B CE80N -- Winter 2002 -- Lecture #5

  36. How Does a Network Work • Interconnecting Networks • A dedicated computer • Special software • Restarts automatically on power up • Goal is to forward packets from one network to another – quickly, efficiently and correctly • Process is called routing • Computers are called routers CE80N -- Winter 2002 -- Lecture #5

  37. How Does a Network Work • Routers – Building blocks of the Internet The Internet is not a conventional network. It consists of thousands of computer networks interconnected by dedicated special purpose computers calledrouters • Routers can interconnect LANs and WANs CE80N -- Winter 2002 -- Lecture #5

  38. How Does a Network Work Net LAN LAN Net LAN LAN Wide Area Backbone LAN LAN LAN Net  A Happy Router CE80N -- Winter 2002 -- Lecture #5

  39. How Does the Network Work? • Interconnecting networks was a revolutionary idea…. • Simply connect to your closest neighbor and you are in! • Issues now arise • Privacy • Politics • Borders CE80N -- Winter 2002 -- Lecture #5

  40. How Does a Network Work? • Getting connected... • Connection service provided by an Internet Service Provider (ISP) • Provides connection to the Internet • ISP agrees to route your packets to/from Internet • Email server • Web page presence • Other file space CE80N -- Winter 2002 -- Lecture #5

  41. How Does a Network work • Getting connected… • ISPs …. • Provides access to/from your machine • “The Last Mile”.. • Dial-up modem, ADSL, wireless, cable modem • It isn’t free… • Pay for the Internet connection • Pay for “The last mile”… CE80N -- Winter 2002 -- Lecture #5

  42. How Does a Network Work ? • Getting Connected • Direct line, leased digital circuit • 24/7 availability; very expensive -- $500+/mo • High speed 1.5Mbps  …. • Dial-up modem • $10-20/mo; not 24/7 • Slow link (56Kbps, or less) CE80N -- Winter 2002 -- Lecture #5

  43. How Does the Network Work ? • Getting connected… • New technologies • (A)DSL – (Asymmetric) Digital Subscriber Line • 24/7; $50/mo; medium speed (384Kbps) • Multiplexes data and voice on same wires • Cable modem • 24/7; $50/mo; medium to high speed (  10Mbps) • Wire already in place in most (suburban) homes • Multiplexes data and TV signals on same wire • Wireless • 24/7; $??; slow to medium (10Kbps  10Mbps) CE80N -- Winter 2002 -- Lecture #5

  44. Residential access: point to point access Dialup via modem up to 56Kbps direct access to router (conceptually) ISDN: integrated services digital network: 128Kbps all-digital connect to router (overcome by ADSL) ADSL: asymmetric digital subscriber line up to 1 Mbps home-to-router up to 8 Mbps router-to-home ADSL deployment: happening How Does the Network Work? CE80N -- Winter 2002 -- Lecture #5

  45. Residential access: cable modems HFC: hybrid fiber coax asymmetric: up to 1 Mbps upstream, 10 Mbps downstream network of cable and fiber attaches homes to ISP router shared access to router among homes issues: congestion, dimensioning deployment: available via cable companies How Does the Network work ? CE80N -- Winter 2002 -- Lecture #5

  46. Institutional access: local area networks Corporate/University local area network (LAN) connects end system to edge router Ethernet: shared or dedicated cable connects end system and router 10 Mbs, 100Mbps, Gigabit Ethernet deployment: institutions, home LANs soon How Does the Network Work? CE80N -- Winter 2002 -- Lecture #5

  47. Wireless access networks shared wireless access network connects end system to router wireless LANs: radio spectrum replaces wire e.g., Lucent Wavelan 10 Mbps 802.11 wider-area wireless access CDPD: wireless access to ISP router via cellular network router base station mobile hosts How Does the Network Work? CE80N -- Winter 2002 -- Lecture #5

  48. physical link: transmitted data bit propagates across link guided media: signals propagate in solid media: copper, fiber unguided media: signals propagate freely e.g., radio Twisted Pair (TP) two insulated copper wires Category 3: traditional phone wires, 10 Mbps Ethernet Category 5 TP: 100Mbps ethernet Physical Media CE80N -- Winter 2002 -- Lecture #5

  49. Coaxial cable: wire (signal carrier) within a wire (shield) baseband: single channel on cable broadband: multiple channels on cable bidirectional common use in 10Mbs Ethernet Physical Media: coax, fiber Fiber optic cable: • glass fiber carrying light pulses • high-speed operation: • 100Mbps Ethernet • high-speed point-to-point transmission (e.g., 5 Gbs) • low error rate CE80N -- Winter 2002 -- Lecture #5

  50. signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: Line of sight obstruction by objects Reflection Interference Physical media: WireLess Radio link types: • microwave • e.g. up to 45 Mbps channels • LAN (e.g., waveLAN) • 2Mbps, 11Mbps .. 54Mbps • wide-area (e.g., cellular) • e.g. CDPD, 10’s Kbps • satellite • up to 50Mbps channel (or multiple smaller channels) • 270 msec end-to-end delay • geosynchronous versus LEOS CE80N -- Winter 2002 -- Lecture #5

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