Introduction to Computer Networking Guy Leduc …

1 11: Introduction1-1 Introduction to Computer NetworkingGuy LeducChapter 1: Computer Networks and the InternetComputer Networking : A Top Down Approach, 7thedition. Jim Kurose, Keith RossAddison-Wesley, April 2016 From Computer Networking , by Kurose&RossIntroduction1-2 chapter 1: IntroductionOur goal:qget feel and terminologyqmore depth, detail laterin courseqapproach:vuse Internet as exampleOverview:qwhat s the Internet?qwhat s a protocol?qnetwork edge: end systems, access network, physical mediaqnetwork core: packet/circuit switching, Internet structureqperformance: loss, delay, throughputqprotocol layers, service modelsqhistory2 From Computer Networking , by Kurose&RossIntroduction1-3 chapter 1: What isthe Internet?

2 Edge-end systems, access networks, core-packet switching vs circuit switching, network , loss and throughput in layers, service From Computer Networking , by Kurose&RossIntroduction1-4 What s the Internet: nuts and bolts viewqmillions of connected computing devices: hosts =end systems running network appsqcommunication links fiber, copper, radio, satellite transmission rate (bps) delay error rateqpacket switches:forward packets (chunks of data) routersand switcheswiredlinkswirelesslinksroutermob ile networkglobal ISPregional ISPhome networkinstitutionalnetworksmartphonePCs erverwirelesslaptop3 From Computer Networking , by Kurose&RossIntroduction1-5 Fun internet appliancesIP picture frameWeb-enabled toaster +weather forecasterInternet phonesInternet refrigeratorSet top box: watch,control cable TV remotelyTweet-a-watt: monitor energy use From Computer Networking , by Kurose&RossIntroduction1-6 What s the Internet.

3 Nuts and bolts viewqInternet: network of networks vInterconnected ISPs (Internet Service Providers)qprotocolscontrol sending, receiving of , TCP, IP, HTTP, Skype, WiFi, EthernetqInternet standardsvRFC: Request for commentsvIETF: Internet Engineering Task Forcemobile networkglobal ISPregional ISPhome networkinstitutionalnetwork4 From Computer Networking , by Kurose&RossIntroduction1-7 What s the Internet: a service viewqInfrastructure that provides services to applications:vWeb, VoIP, email, games, e-commerce, social nets.

4 Qprovides programming interface to appsvhooks that allow sending and receiving app programs to connect to Internetvprovides service options, analogous to postal servicemobile networkglobal ISPregional ISPhome networkinstitutionalnetwork From Computer Networking , by Kurose&RossIntroduction1-8 What s a protocol?human protocols:q what s the time? q I have a question specific msgs specific actions taken when msgs received, or other eventsnetwork protocols:qmachines rather than humansqall communication activity in Internet governed by protocolsprotocolsdefine format, orderof msgssent and receivedamong network entities, and actions takenon msg transmission, receipt5 From Computer Networking , by Kurose&RossIntroduction1-9 What s a protocol?

5 A human protocol and a Computer network protocol:Q:Other human protocols? HiHiGot thetime?2:00timeGet connectionrequestTCP connectionresponse<file> From Computer Networking , by Kurose&RossIntroduction1-10 chapter 1: What isthe Internet? Network edge-end systems, access networks, Network core-packet switching vs circuit switching, network , loss and throughput in layers, service From Computer Networking , by Kurose&RossIntroduction1-11A closer look at network structurenetwork edge: hosts: clients and servers servers often in data centersaccess networks, physical media:wired, wireless communication linksnetwork core.

6 Interconnected routers network of networksmobile networkglobal ISPregional ISPhome networkinstitutionalnetwork From Computer Networking , by Kurose&RossIntroduction1-12 Access networks and physical mediaQ: How to connect end systems to edge router?qresidential access netsqinstitutional access networks (school, company)qmobile access networkskeep in mind: qdata rate (in bits per second) of access network?qshared or dedicated?7 From Computer Networking , by Kurose&RossIntroduction1-13qUses existing telephony infrastructurevHome is connected to central officeqUp to 56 Kbps direct access to router (often less)qCan t surf and phone at same time: not always on Historically: Dial-up ModemtelephonenetworkInternethomedial-up modemISPmodemhomePCcentral office From Computer Networking , by Kurose&RossIntroduction1-14 Modems.

7 Types of Modulations0000000011111 Phase changesPhase modulationA binary signalAmplitude modulationFrequency modulationFrom Computer Networks, by Tanenbaum Prentice Hall8 From Computer Networking , by Kurose&RossIntroduction1-15 Combination of Amplitude and Phase Modulations1 symbol= 4 bits1 symbol= 2 bits 2 bits/baud Consider a 2400 baud-line:EncodingData rate (bps)Modulation technique2 kbpsQPSK: QuadraturePhase Shift Keying4 kbpsQAM-16: QuadratureAmplitude Modulation6 kbpsQAM-64 Data-rate = baud-rate x(nr. of bits/symbol)1 symbol= 6 bits1 baud = 1 symbol per second 1 bit per second1 symbol = (co)sine withsome amplitude and phaseFrom Computer Networks, by Tanenbaum Prentice HallIntroduction1-16 Upper bounds on the baud-rate and the data-rateqThe baud-rate (expressed in bauds, number of symbols per second) is limited by the frequency bandwidth (H) of the physical channel (H is expressed in Hertz)vNyquist law.

8 Baud-rate 2 H Means that the symbol duration Dcannot be smaller than 1/2 HvThis law does not constrain the data-rate encoding could use an arbitrarily large number of bits per baudqThe data-rate (expressed in bps, bits per second) is however limited!vThe upper bound is the capacityof the channelvGiven by Shannonlaw: data-rate H log2(1 + S/N) S = (Average received) Signal power, N = (Average) Noise powervDepends on frequency bandwidth and Signal-to-Noise (S/N) ratio Dial-up modem example: H = 4 kHz and S/N = 1000 give data-rate ~ 40 kbps Note: when H and S are > 0, capacity is always > 0, for all N > 09 From Computer Networking , by Kurose&RossIntroduction1-17 Access net.

9 Digital subscriber line (DSL)central officeISPtelephonenetworkDSLAM voice, data transmittedat different frequencies overdedicated line to central officequse existingtelephone line to central office DSLAM data over DSL phone line goes to Internet voice over DSL phone line goes to telephone net data and voice sent/received over different frequency bands data frequency band much larger => capacity much largerqtypically a few Mbps upstream transmission rateqtypically 20-30 Mbps downstream transmission rateDSLmodemsplitterDSL access multiplexer From Computer Networking .

10 By Kurose&RossIntroduction1-18 DSL: data rate versus distanceOver category 3 copper twisted pairs (used in telephone networks)From Computer Networks, by Tanenbaum Prentice HallIf distance increases, signal attenuates, so S/N decreases,leading to a lower data rate (Shannon)10 From Computer Networking , by Kurose& headendChannelsVIDEOVIDEOVIDEOVIDEOVIDEO VIDEODATADATACONTROL123456789 Frequency Division Multiplexing (FDM):different channels transmitted in different frequency bands(like in DSL)Access net: cable network From Computer Networking , by Kurose&RossIntroduction1-20data, TV transmitted at different frequencies over shared cable distribution headendCMTSISP cable modemtermination systemqHFC: hybrid fiber coax asymmetric: up to 30 Mbps downstream transmission rate, 2 Mbps upstream transmission rateqnetwork of cable, fiber attaches homes to ISP router homes share access networkto cable headend unlike DSL, which has dedicated access to central officeAccess net.