CE80N Introduction to Networks & The Internet

CE80NIntroduction to Networks&The InternetDr. Chane L. FullmerUCSCWinter 2002

CE80N -- Winter 2002 -- Lecture #5

Next Week Inside the InternetJan 22 (T) Inside the InternetChapter 15, IP: Software to Create a Virtual NetworkJan 24 (Th) Inside the InternetChapter. 16, TCP: Software For Reliable CommunicationChapter. 19, Why the Internet Works Well


More Internet History1961: Kleinrock - queueing theory shows effectiveness of packet-switching1964: Baran - packet-switching in military nets1967: ARPAnet conceived by Advanced Research Projects Agency1969: first ARPAnet node operational

1972: ARPAnet demonstrated publiclyNCP (Network Control Protocol) first host-host protocol first e-mail programARPAnet has 15 nodes1961-1972: Early packet-switching principles


More Internet History1970: ALOHAnet satellite network in Hawaii1973: Metcalfes PhD thesis proposes Ethernet1974: Cerf and Kahn - architecture for interconnecting networkslate70s: proprietary architectures: DECnet, SNA, XNAlate 70s: switching fixed length packets (ATM precursor)1979: ARPAnet has 200 nodesCerf and Kahns internetworking principles:minimalism, autonomy - no internal changes required to interconnect networksbest effort service modelstateless routersdecentralized controldefine todays Internet architecture1972-1980: Internetworking, new and proprietary nets


More Internet History1982: smtp e-mail protocol defined 1983: deployment of TCP/IP1983: DNS defined for name-to-IP-address translation1985: ftp protocol defined1988: TCP congestion controlnew national networks: Csnet, BITnet, NSFnet100,000 hosts connected to confederation of networks1980-1990: new protocols, a proliferation of networks


More Internet HistoryEarly 1990s: ARPAnet decommissioned1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)early 1990s: WWWhypertext [Bush 1945, Nelson 1960s]HTML, http: Berners-Lee1994: Mosaic, later Netscapelate 1990s: commercialization of the WWWLate 1990s:est. 50 million computers on Internetest. 100 million+ usersbackbone links running at 1 Gbps

1990s: commercialization, the WWW


ReadingChapter 12, Packet SwitchingChapter 13, A Network of NetworksChapter 14, ISPs and Network Connections


How does a Network work?


How Does the Network work ?Circuit switchingNetwork resources reserved and dedicated from sender to receiver (circuit)Control signaling and data transfers are separatedControl information processing at circuit setup and termination


How Does the Network Work?Sharing is a good thing..Saves moneyOne public phone vs. a cell phone for each individualOne central conveyor belt in warehouseBut, costs timeWaiting for the resource to be freeLong winded conversationalistBig order on the conveyor belt


How Does the Network WorkSharing by taking turnsConveyor belt modelAllow packages to be interspersed Individual orders packages are multiplexed with others onto the moving belt..Networks use a similar ideaPacket SwitchingPacketize data to transferMultiplex it onto the wire


How Does the Network Work?Packet Switching ExampleADBC


How Does the Network Work?Packet SwitchingAvoids some delaysResource is shared by multiplexing packetsShort messages do not have to wait for long ones to complete.OverheadPacketizing does not come for freeHeader with labeling information is added


How Does a Network WorkPacket SwitchingLabeling (Header information)Source (senders) addressDestination (recipients) addressPacket sizeSequence numberError checking information


How Does a Network WorkPacket SwitchingComputer AddressesEach 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.


How Does a Network Work?Packet SwitchingPacket sizes are variableThere is a maximum packet sizeMaximum transmission unit (MTU)No minimum sizeBut, header size is fixed -- ~40 bytesTransmission seems fast1000+ packets/second on campus LAN


How Does a Network WorkPacket SwitchingSharing is automatic and fairHardware handles the sharingAdapts as more/less computers are activeRemote devices can be sharedPrintersMust be network smartFile Systems


Compare and ContrastCircuit-Switchedguaranteed transmissionlarge setup delaysreliable connectionquality-of-serviceidle time is wastedbandwidth granularity problemPacket-Switchedsmall setup delays, header overheadunreliable connectionefficient use of available bandwidthcongestion (queues) result in dropped packets


How Does a Network Work?Packet Switching and the InternetAll 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.


The Network Coremesh of interconnected routersthe fundamental question: how is data transferred through net?circuit switching: dedicated circuit per call: telephone netpacket-switching: data sent thru net in discrete chunks


Network Core: Circuit SwitchingEnd-end resources reserved for calllink bandwidth, switch capacitydedicated resources: no sharingcircuit-like (guaranteed) performancecall setup required


Network Core: Circuit Switchingnetwork resources (e.g., bandwidth) divided into piecespieces allocated to callsresource piece idle if not used by owning call (no sharing)dividing link bandwidth into piecesfrequency divisiontime division


Network Core: Packet Switchingeach end-to-end data stream is divided into packetsuser packets share network resources each packet uses full link bandwidth resources used as neededresource contention: aggregate resource demand can exceed amount availablecongestion: packets queue, wait for link usestore and forward: packets move one hop at a timetransmit over linkwait turn at next link


Network Core: Packet SwitchingPacket-switching versus circuit switching:Personal Driving analogyother human analogies?


Network Core: Packet SwitchingStore & Forward Behavior


Packet switching versus circuit switching1 Mbit linkeach user: 100Kbps when activeactive 10% of time

circuit-switching: 10 userspacket switching: with 35 users, probability > 10 active less that .004Packet switching allows more users to use network!N users1 Mbps link


Packet switching versus circuit switchingGreat for bursty dataresource sharingno call setupExcessive congestion: packet delay and lossprotocols needed for reliable data transfer, congestion controlQ: How to provide circuit-like behavior?bandwidth guarantees needed for audio/video appsstill an unsolved problemIs packet switching a slam dunk winner?


Packet-switched networks: routingGoal: move packets among routers from source to destinationwell look at a couple of path selection algorithmsdatagram network: destination address determines next hoproutes may change during sessionanalogy: driving, asking directions without a map! virtual circuit network: each packet carries tag (virtual circuit ID), tag determines next hopfixed path determined at call setup time, remains fixed thru callrouters maintain per-call state


Access networks and physical mediaQ: How to connect end systems to edge router?residential access netsinstitutional access networks (school, company)mobile access networksKeep in mind: bandwidth (bits per second) of access network?shared or dedicated?


Delay in packet-switched networkspackets experience delay on end-to-end pathfour sources of delay at each hopProcessing delay: check bit errorsdetermine output linkQueueing delay:time waiting at output link for transmission depends on congestion level of router


Delay in packet-switched networksTransmission delay:R=link bandwidth (bps)L=packet length (bits)time to send bits into link = L/RPropagation delay:d = length of physical links = propagation speed in medium (~3x108 m/sec)propagation delay = d/s


Queueing delay (revisited)R=link bandwidth (bps)L=packet length (bits)l = average packet arrival ratetraffic intensity = l(L/R)l(L/R) ~ 0: average queueing delay smalll(L/R) -> 1: delays become largel(L/R) > 1: more work arriving than can be servicedaverage delay approaches infinity!l


How Does a Network Work?Various network technologies are incompatibleMany tradeoffs cost, speed, extensibility, etc..It is impractical, or infeasible, to require all computers to use the same network technologyNeeds of Engineering vs. Administration


How Does a Network WorkExtending a network is simple.

NetworkPOTSDirect WireOptical FiberDial-Up LineWireless


How Does A Network WorkA computer can have multiple NICsEach NIC can connect to a separate networkNetworkANetworkB


How Does a Network WorkInterconnecting NetworksA dedicated computerSpecial softwareRestarts automatically on power upGoal is to forward packets from one network to another quickly, efficiently and correctlyProcess is called routingComputers are called routers


How Does a Network WorkRouters Building blocks of the InternetThe Internet is not a conventional network. It consists of thousands of computer networks interconnected by dedicated special purpose computers called routersRouters can interconnect LANs and WANs


How Does a Network WorkWide Area BackboneLANLANLANLANLANLANLANNetNetNet A Happy Router


How Does the Network Work?Interconnecting networks was a revolutionary idea.Simply connect to your closest neighbor and you are in!Issues now arisePrivacyPoliticsBorders


How Does a Network Work?Getting connected... Connection service provided by an Internet Service Provider (ISP)Provides connection to the InternetISP agrees to route your packets to/from InternetEmail serverWeb page presenceOther file space


How Does a Network workGetting connectedISPs .Provides access to/from your machineThe Last Mile..Dial-up modem, ADSL, wireless, cable modemIt isnt freePay for the Internet connectionPay for The last mile


How Does a Network Work ?Getting ConnectedDirect line, leased digital circuit24/7 availability; very expensive -- $500+/moHigh speed 1.5Mbps .Dial-up modem$10-20/mo; not 24/7Slow link (56Kbps, or less)


How Does the Network Work ?Getting connectedNew technologies(A)DSL (Asymmetric) Digital Subscriber Line24/7; $50/mo; medium speed (384Kbps)Multiplexes data and voice on same wiresCable modem24/7; $50/mo; medium to high speed ( 10Mbps)Wire already in place in most (suburban) homesMultiplexes data and TV signals on same wireWireless24/7; $??; slow to medium (10Kbps 10Mbps)


How Does the Network Work?Residential access: point to point accessDialup via modemup 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 lineup to 1 Mbps home-to-routerup to 8 Mbps router-to-homeADSL deployment: happening


How Does the Network work ?Residential access: cable modemsHFC: hybrid fiber coaxasymmetric: up to 1 Mbps upstream, 10 Mbps downstreamnetwork of cable and fiber attaches homes to ISP routershared access to router among homesissues: congestion, dimensioning deployment: available via cable companies


How Does the Network Work?Institutional access: local area networksCorporate/University local area network (LAN) connects end system to edge routerEthernet: shared or dedicated cable connects end system and router10 Mbs, 100Mbps, Gigabit Ethernetdeployment: institutions, home LANs soon


How Does the Network Work?Wireless access networksshared wireless access network connects end system to routerwireless LANs:radio spectrum replaces wiree.g., Lucent Wavelan 10 Mbps802.11wider-area wireless accessCDPD: wireless access to ISP router via cellular network


Physical Mediaphysical link: transmitted data bit propagates across linkguided media: signals propagate in solid media: copper, fiberunguided media: signals propagate freely e.g., radioTwisted Pair (TP)two insulated copper wiresCategory 3: traditional phone wires, 10 Mbps EthernetCategory 5 TP: 100Mbps ethernet


Physical Media: coax, fiberCoaxial cable:wire (signal carrier) within a wire (shield)baseband: single channel on cablebroadband: multiple channels on cablebidirectionalcommon use in 10Mbs EthernetFiber optic cable:glass fiber carrying light pulseshigh-speed operation:100Mbps Ethernethigh-speed point-to-point transmission (e.g., 5 Gbs)low error rate


Physical media: WireLesssignal carried in electromagnetic spectrumno physical wirebidirectionalpropagation environment effects:Line of sight obstruction by objectsReflection Interference Radio link types:microwavee.g. up to 45 Mbps channelsLAN (e.g., waveLAN)2Mbps, 11Mbps .. 54Mbpswide-area (e.g., cellular)e.g. CDPD, 10s Kbpssatelliteup to 50Mbps channel (or multiple smaller channels)270 msec end-to-end delaygeosynchronous versus LEOS


How Does a Network Work?Instantaneous Access & Continuous AvailabilityCompare Dial-up vs dedicated connection

A dedicated Internet connection that provides instantaneous access 24/7 changes the way people view the Internet, because it encourages frequent and casual use.


How Does the Network Work?SummaryCircuit SwitchingReserves resourcesPacket SwitchingShares resourcesIncreased overhead headersPackets are labeled with destination infoEfficient resources used as needed Unreliable packets can be dropped


How Does the Network Work?SummaryPacket SwitchingStore and ForwardPackets move one hop at a timeDecisions are made at each hopDelay ..Processing delayQueueing delayTransmission delayPropagation delay


How Does the Network Work?SummaryA router is used to interconnect networksLANs to LANs or LANs to WANsRouters forward packets from one network to anotherProcess is called RoutingRouters are the building blocks of the Internet


How Does the Network Work?SummaryISPs provide the connection service to access the InternetThe Last MileDialupADSLCable modemWirelessAlso may provide email, web space or other services


GlossaryDestination AddressA numeric value in a packet that specifies the computer to which the packet has been sent.Network Printer A printer that attaches directly to a network where it can be accessed by any computer on the network.


GlossaryPacket Used informally to describe the unit of data sent across a packet switching network. Packet Switching A technique used on computer networks that requires a computer to divide a message into small packets of data before sending them.


GlossaryFibera thin, flexible glass fiber used to transmit information using pulses of light.Network of networksA phrase used to describe the Internet.Source Address The address of the computer sending data.


GlossaryRouteIn general, a route is the path that network traffic takes from its source to its destination.RouterA special purpose, dedicated computer that attaches to two or more networks and routes IP datagrams from one to the other.


GlossaryCable Modem A device that allows Internet service to be provided over the same coaxial cable wiring used for cable television.Dial-up Access A technique used to access the Internet using a conventional telephone call.


Glossary(A)DSL ((Asymmetric)Digital Subscriber Line) Any of several technologies used to deliver high-speed Internet access over the same wires used for telephone service.Wireless network A network that uses radio waves to transmit in place of wires.


Documents

CE80N Introduction to Networks & The Internet