UCBEECS 122Lecture 2EECS122 – Lecture 2Department of Electrical Engineering and Computer SciencesUniversity of CaliforniaBerkeleyEECS 122 - UCB 2TOC: Applications/DesignWeb BrowsingTelephone CallMultiplexingProtocolsIETFEECS 122 - UCB 3Applications: Web BrowsingExampleLocating Resource: DNSConnectionEnd-to-endPacketsBitsPoints to rememberEECS 122 - UCB 4Click Link or URLà get content from localor remote computerURL:http://www.google.com/stringSpecifies- Protocol: http- Computer: www.google.com- StringComputer (server) selects contents based on stringWeb: ExampleEECS 122 - UCB 5Web: Locating Resourcewww.google.com is the name of a computerNetwork uses IP addressesTo find the IP address, the application uses a hierarchical directory service called theDomain Name Systemlocalcomhostwww.google.com?IP = a.b.c.dIP = a.b.c.dwww.google.com?EECS 122 - UCB 6Web: ConnectionThe protocol (http) sets up a connection between the host and cnn.com to transfer the pageThe connection transfers the page as a byte stream, without errors: pacing + error controlHostcnn.comconnectOKget pagepage; closeUCBEECS 122Lecture 2EECS 122 - UCB 7Web: End-to-endThe byte stream flows from end to end across many links and switches: routing (+ addressing)That stream is regulated and controlled by both ends: retransmission of erroneous or missing bytes; flow controlEnd-to-end pacing andflow controlRoutingwww.google.comhostEECS 122 - UCB 8Web: PacketsThe network transports bytes grouped into packetsThe packets are “self-contained” and routers handle them one by oneThe end hosts worry about errors and flow control:n Destination checks packet for errors (using error detection code CKS) and sends ACKswith sequence number #n Source retransmits packets that were not ACKed and adjusts rate of transmissionsCA | B | # , CKS | bytesB Cwww.google.comIP address: AHostIP address: BDestinationNext HopEECS 122 - UCB 9Web: BitsEquipment in each node sends the packets as a string of bitsThat equipment is not aware of the meaning of the bits01011...011...110Transmitter Physical Medium Receiver01011...011...110OpticalCopperWirelessEECS 122 - UCB 10Web: Points to rememberSeparation of tasksn send bits on a link: transmitter/receiver [clock, modulation,…]n send packet on each hop [framing, error detection,…]n send packet end to end [addressing, routing]n pace transmissions [detect congestion]n retransmit erroneous or missing packets [acks, timeout]n find destination address from name [DNS]Scalabilityn routers don’t know about connectionsn names and addresses are hierarchicalEECS 122 - UCB 11Applications: TelephoneTelephone NetworkDialing a NumberSetting up a CircuitPhone ConversationReleasing the CircuitEECS 122 - UCB 12Telephone: Telephone NetworkSwitchesNetworkLogic DiagramUCBEECS 122Lecture 2EECS 122 - UCB 13Telephone Network: Switches5ESS (Lucent)DMS100 (Nortel)EECS 122 - UCB 14Telephone Network: NetworkEECS 122 - UCB 15Telephone Network: Logic DiagramEECS 122 - UCB 16Telephone: Dialing a NumberA Off-HookS1 ListensA dialsS1 RegistersABS1EECS 122 - UCB 17Telephone: Setting Up a CircuitABringCircuit = capacity to carry one phone call (shown by thin lines)Circuit is allocated to the call between A and BCircuits are not shared; they are dedicated. EECS 122 - UCB 18Telephone: Phone ConversationABVoice signals use the reserved circuitsUCBEECS 122Lecture 2EECS 122 - UCB 19Telephone: Release CircuitsABA or B goes Off-HookCircuits get releasedEECS 122 - UCB 20Design: MultiplexingOverviewOperationsTDM/FDMStatistical MultiplexingAnalysis of TDM/FDMAnalysis of Statistical MultiplexingEECS 122 - UCB 21Multiplexing: OverviewNetworks are shared resourcesSharing via multiplexingFundamental Question:how to achieve controlled sharingEECS 122 - UCB 22Multiplexing: OperationsMethods for sharing a communication channelTradeoff between utilization and predictabilityCommon Approaches:n TDM (time-division multiplexing)n Statistical MultiplexingEECS 122 - UCB 23MPX: Time Division MultiplexingMultiplexern linksrate r bpseach1 link, rate nr bpsFrame:Time “slots” are reservedbps = bits per secondEECS 122 - UCB 24MPX: Statistical MultiplexingMultiplexern linksany rate1 link, any rateTraceExcerpt:Variable-sized “packets” of data are interleavedbased on the statistics of the sendersUCBEECS 122Lecture 2EECS 122 - UCB 25MPX: Analysis of TDM/FDMTDM, FDM (frequency division multiplexing), and WDM (wavelength) may under-utilize channel with idle sendersApplicable only to fixed numbers of flowsRequires precise timer (or oscillator and guard bands for FDM)Resources are guaranteedEECS 122 - UCB 26MPX: Analysis of SMTraffic is sent on demand, so channel is fully utilized if there is traffic to sendAny number of flowsNeed to control sharing:n packets are limited in sizen prevents domination of single senderResources are not guaranteedEECS 122 - UCB 27Design: ProtocolsDefinitionExamplesStandardsEECS 122 - UCB 28Protocols: DefinitionAgreement dictating the form and function of data exchanged between two (or more) parties to effect a communicationTwo parts: syntax and semanticsn syntax: where bits gon semantics: what they mean and what to do with themEECS 122 - UCB 29Protocols: ExamplesInternet Protocol (IP)n if you can generate and understand IP, you can be on the Internetn media, OS, data rate independentTCP and HTTPn if you can do these, you are on the webEECS 122 - UCB 30Protocols: StandardsNew functions require new protocolsThus there are many (e.g. IP, TCP, UDP, HTTP, RIP, OSPF, IS-IS, SMTP, SNMP, Telnet, FTP, DNS, NNTP, NTP, BGP, PIM, DVMRP, ARP, NFS, ICMP, IGMP)Specifications do not change frequentlyOrganizations: IETF, IEEE, ITUUCBEECS 122Lecture 2EECS 122 - UCB 31Design: The IETFSpecifies Internet-related protocolsProduces “RFCs” (www.rfc-editor.org)Quotation from IETF T-shirt:We reject kings, presidents and voting.We believe in rough consensus and running code.--- David
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