Introduction to Packet-Switched Networks

Competition in Telecoms Recitation #2 Agenda • Introduction to Packet-Switched Networks 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 backbone lines (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 Ring LAN Architectures 4 ‘logical architectures’: – – – – Bus Logical Ring Star Tree 3 types of data transmission – Unicast: single source to single destination – Multicast: single source to specific subset of nodes – Broadcast: single source sent to all nodes OSI Reference Model • International Standards Organization (ISO) • OSI (Open Systems Interconnection) • Objective: Interoperability – Standard description for transmission of messages between 2 points 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 computer OSI Layer Overview Layer Functions Sample Protocols Layer 7: Application Enable Applications to Access the Network Stack DNS, FTP, Winsock API, SMTP Layer 6: Presentation Coding and conversion functions for Application Layer Data MPEG, GIF, JPEG, TIFF Layer 5: Session Establishing, managing and terminating sessions AppleTalk, SCP Layer 4: Transport Packetizes data from the Session layer and ensures error-free delivery TCP, UDP Layer 3: Network Addressing, routing, packet switching, and data congestion IP, IPV6 Layer 2: Data Link Packets ÅÆ Bits SLIP, PPP, Ethernet Layer 1: Physical Transmit bits over cable (voltage, timing, data rates, maximum distance, physical connectors) 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 end Layer 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 forwarding Ethernet Token Ring Local Bridging Bridge Bridge Bridge Remote Bridging Layer 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: 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 path