15.020 Competition in TelecomsRecitation #2AgendaWhat is an Internetwork?Wide Area Networks (WANs)Metropolitan Area Networks (MANs)Local Area Networks (LANs)LAN ArchitecturesOSI Reference ModelOSI Reference ModelEncapsulationOSI Layer OverviewLayer 1 (Physical)Layer 2 (Data Link Layer)Layer 2 (Data Link Layer)Layer 3 (Network)Where does Each Protocol Fit?15.020 Competition in TelecomsRecitation #2Othman LarakiAgenda• Introduction to Packet-Switched NetworksWhat is an Internetwork?For this diagram, see Figure 1-1 in:Cisco Systems, Internetworking Technologies Handbook, 2002. http://www.cisco.com/univercd/Connecting different devices, using different technologies to each other and having them work together and function as a single large network.Wide Area Networks (WANs)• A geographically dispersed telecommunications network, more broad than a LAN• May be privately owned or rented, but usually connotes the inclusion of public networks.• WAN technologies function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.Metropolitan Area Networks (MANs)• A network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN).• Usually an interconnection of networks in a city into a single larger network (which may then also offer efficient connection to a wide area network)• also the interconnection of several LANs by bridging them with backbonelines (sometimes referred to as a campus network).Local Area Networks (LANs)• Interconnect individual users so that they can exchange data and share peripheral devices over small geographic area• Computers use underlying ‘protocols’ to communicate across a LAN – at lowest 2 layers of OSI Model• High-speed, fault-tolerant• 2 main methods of accessing the physical medium:– Carrier sense Multiple Access with Collision Detect (CSMA/CD)• Ethernet– Token passing• Token RingLAN Architectures4 ‘logical architectures’:–Bus– Logical Ring–Star–Tree3 types of data transmission– Unicast: single source to single destination– Multicast: single source to specific subset of nodes– Broadcast: single source sent to all nodesOSI Reference Model• International Standards Organization (ISO)• OSI (Open Systems Interconnection)• Objective: Interoperability– Standard description for transmission of messages between 2points in a telecommunication network– Consistent interaction of products• Core Concept: Layering– Divide communication between 2 users into layers, each layer adding special, related functions: each user’s computer has the 7 layers• Upper 4 layers used whenever a message passes from or to a user• Lower 3 layers used when a message passes through the host computerOSI Reference ModelFor this diagram, see: Dell White Paper: Local Area Networks (1997).EncapsulationFor this diagram, see Figure 1-6 in:Cisco Systems, Internetworking Technologies Handbook, 2002. http://www.cisco.com/univercd/OSI Layer OverviewLayer Functions Sample ProtocolsLayer 7: Application Enable Applications to Access the Network StackDNS, FTP, Winsock API, SMTPLayer 6: Presentation Coding and conversion functions for Application Layer DataMPEG, GIF, JPEG, TIFFLayer 5: Session Establishing, managing and terminating sessionsAppleTalk, SCPLayer 4: Transport Packetizes data from the Session layer and ensures error-free deliveryTCP, UDPLayer 3: Network Addressing, routing, packet switching, and data congestionIP, IPV6Layer 2: Data Link Packets ÅÆ Bits SLIP, PPP, EthernetLayer 1: Physical Transmit bits over cable (voltage, timing, data rates, maximum distance, physical connectors)Based on: Internetworking Technologies Handbook, 2002. http://www.cisco.com/univercd/Layer 1 (Physical)• Repeater– Interconnect LAN segments– Treat as single cable & retransmits all signals– Prevent signal degradation• Multiplexer– Multiplex: Combine multiple data streams onto 1 or more output channels– Demultiplex: Separate data streams at remote endFor this diagram, see Figure 2-6 in Cisco Systems, Internetworking Technologies Handbook, 2002. http://www.cisco.com/univercd/For this diagram, see Figure 1-19 in Cisco Systems, Internetworking Technologies Handbook, 2002. http://www.cisco.com/univercd/Source: Cisco SystemsLayer 2 (Data Link Layer)Bridges– Transparently connects LAN segments together, forwarding packets destined for the other segment– Operate in software– Can filter out packets that do not need forwardingBridgeLocal BridgingEthernetBridge BridgeBased on Figure 4-1 in Cisco Systems, Internetworking Technologies Handbook, 2002. http://www.cisco.com/univercd/Token RingRemote BridgingLayer 2 (Data Link Layer)LAN Switches– Interconnect multiple LAN segments– Provide dedicated, collision-free communication between network devices– Support for multiple simultaneous conversations– Switch data frames at high speeds (in hardware)– Example: interconnect 10-Mbps & 100-Mbps Ethernet LANs:For this diagram, see Figure 4-4 in:Cisco Systems, Internetworking Technologies Handbook, 2002. http://www.cisco.com/univercd/Layer 3 (Network)• Routers– Analyze network address to make routing decisions– Choose optimum route and forward packet to adjacent router– Use ‘routing protocols’ to define optimal pathFor this diagram, see Figure 2-7 in:Cisco Systems, Internetworking Technologies Handbook, 2002. http://www.cisco.com/univercd/Where does Each Protocol Fit?For this diagram, see the entry for “OSI Reference Model” at SearchNetworking.com,