Page 1Peter A. Steenkiste, SCS, CMU1Lecture 2Protocol StacksPeter SteenkisteDavid EckhardtSchool of Computer ScienceCarnegie Mellon University15-441 Networking, Spring 2006http://www.cs.cmu.edu/~441Peter A. Steenkiste, SCS, CMU2Today’s Lecturez Some history.z What is a protocol.z Protocol stacks.z Standards organizations.z Application layer.Page 2Peter A. Steenkiste, SCS, CMU3Some History: The Early Daysz Early packet switching networks (61-72).» Definition of packet switching» Early DARPA net: up to tens of nodes– single network– discovery of “interesting” applications» Less than 100 years after telephone (Alexander Bell, 1876)zInternetworking (72-80).» Multiple networks with inter-networking: networks are independent, but need some rules for interoperability» Key concepts: best effort service, “stateless” routers, decentralized control (very different from telephones!)» Basis for Internet: TCP, IP, congestion control, DNS, …» Rapid growth: 10 to 100000 hosts in 10 years– Driven by NSF net, research communityPeter A. Steenkiste, SCS, CMU4Next Step:Commercializationz Industry interest in networking encourages first commercial network deployment.» In part also encouraged by NSFNET policieszIntroduction of the Web makes networks more accessible.» Killer application» Good user interface that is accessible to anybody» Network access on every desktop and in every homezToday: e-commerce.» Integral part of the economy» Part of every day life: entertainment, news, ..Page 3Peter A. Steenkiste, SCS, CMU5Current Trendsz Access for mobile users:» 802.11 is becoming ubiquitous» PDA/cellphone accesszNetworked sensors:» Have always existed in “embedded” networks, e.g. X10» Integration into broader network infrastructure nextz What else?Peter A. Steenkiste, SCS, CMU6Alexander Bellversus the Internetz Analog voice versus digital information.z Permanent circuit versus packet switched.Analog Signal“Digital” SignalPgh SFPgh SFPage 4Peter A. Steenkiste, SCS, CMU7Taxonomy of Communication NetworksCommunicationNetworksBroadcastNetworksSwitchedNetworksCircuit-SwitchedNetworksPacket-SwitchedNetworksDatagramNetworksVirtual CircuitNetworksPeter A. Steenkiste, SCS, CMU8Different Network Viewsz A network is a shared infrastructure that supports communication for many users.» Sharing view: how do users share the network?zMany network technologies exist.» Technology view: how do the technologies coexist?z Networks are owned and managed by multiple organizations.» Management view: how does global communication take place?zNetworks cover different geographic areas.» Geographic view: network diameter?z Networks run many protocols that are responsible for different functions.» Protocol view: how are the many protocols coordinated?Page 5Peter A. Steenkiste, SCS, CMU9Protocolsz An agreement between parties on who communication should take place.z Protocols may have to define many aspects of the communication.» Data encoding, language, error recovery, termination conditions, .. z Network protocols can exist between computer programs or hardware components.Can you give mesome directions?Certainly, where would you like to go?Heinz HallGo left atthe next lightThank youPeter A. Steenkiste, SCS, CMU10More on Protocolsz Protocols are the key to interoperability.» The hardware/software of communicating parties are often not built by the same vendor– Sun workstation with PC, 3COM with Cisco bridge, ..» Yet they can communicate because they use the same protocolzProtocols exist at many levels.» Application level protocols, e.g. access to mail, distribution of bboards, web access, ..» Protocols at the hardware level allow two boxes to communicate over a link, e.g. the Ethernet protocol» Intermediate protocols can “add value” to a lower-level protocol, e.g. provide a reliable communication service over an unreliable linkPage 6Peter A. Steenkiste, SCS, CMU11Too Many Network ComponentsApplicationOperating SystemProtocol SoftwareComputerLinksRouter HardwareRouter Software(many protocols)Bridge HW/SWApplicationOperating SystemComputerNetwork InterfacePeter A. Steenkiste, SCS, CMU12What is a Communication Networkz Electrons and photons as communication medium.z Links: fiber, copper, wireless, ..z Switches: electronic, optical, crossbar, Banyan, ..z Protocols: Ethernet, X.25, SONET, Framerelay, IP, TCP, HTTP, …z Functionality: routing, error control, flow control, congestion control, QoS, security, ..z Applications: FTP, web, games, telephone, video streaming, ..Page 7Peter A. Steenkiste, SCS, CMU13How to Organize the Network?Web FTP VoiceTelnetTw. Pair Coax WirelessOpticalVideoPeter A. Steenkiste, SCS, CMU14Try Again:How to Organize the Network?Web FTP VoiceTelnetTw. Pair Coax WirelessOpticalIntermediate LayerPage 8Peter A. Steenkiste, SCS, CMU15Types of Protocolsz Core network: responsible for transferring data between a sending and receiving host.z End-to-end protocols: present a network service to applications and users.» May add value to the core network protocolshosthosthosthosthosthosthostPeter A. Steenkiste, SCS, CMU16Protocol andService LevelsApplicationEnd-to-endCoreNetworkPage 9Peter A. Steenkiste, SCS, CMU17A Layer Network ModelThe Open Systems Interconnection (OSI) Model.ApplicationApplicationPresentationPresentationSessionSessionTransportTransportNetworkNetworkData linkData linkPhysicalPhysical1234567NetworkNetworkData linkData linkPhysicalPhysicalApplicationApplicationPresentationPresentationSessionSessionTransportTransportNetworkNetworkData linkData linkPhysicalPhysicalPeter A. Steenkiste, SCS, CMU18OSI Motivationz Standard way of breaking up a system in a set of components, but the components are organized as a set of layers.» Only horizontal and vertical communication» Components/layers can be implemented and modified in isolationz Each layer offers a service to the higher layer, using the services of the lower layer.z “Peer” layers on different systems communicate via a protocol.» higher level protocols (e.g. TCP/IP, Appletalk) can run on multiple lower layers» multiple higher level protocols can share a single physical networkPage 10Peter A. Steenkiste, SCS, CMU19OSI Functionsz (1) Physical: transmission of a bit stream.z (2) Data link: flow control, framing, error detection.z (3) Network: switching and routing.z (4) Transport: reliable end to end delivery.z (5) Session: managing logical connections.z (6) Presentation: data transformations.z
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