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Packet-Switched Networks

Packet-Switched Networks. Communication Networks. A generic communication network:. end system. Communication Network. node. Other names for “end system”: station, host, terminal Other names for “node”: switch, router , gateway. Taxonomy of Networks.

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Packet-Switched Networks

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  1. Packet-Switched Networks ECE 1545

  2. Communication Networks • A generic communication network: end system CommunicationNetwork node Other names for “end system”: station, host, terminal Other names for “node”: switch, router, gateway ECE 1545

  3. Taxonomy of Networks • Communication networks can be classified based on the way in which the nodes exchange information: Communication Network Circuit-SwitchedNetwork Packet-SwitchedNetwork Datagram Network Virtual Circuit Network FrequencyDivisionMultiplexing Time DivisionMultiplexing Wavelength DivisionMultiplexing ECE 1545

  4. Packet Switching • Data are sent as formatted bit-sequences, so-called packets • Packets have the following structure: • Header and Trailer carry control information • Each packet is passed through the network from node to node along some path (Forwarding/Routing) • At each node the entire packet is received, stored briefly, and then forwarded to the next node (Store-and-Forward Networks) • Packet transmission is never interrupted (no preemption) • No capacity is allocated for packets Header Data Trailer ECE 1545

  5. A Packet Switch ECE 1545

  6. Packet 1 Packet 1 Packet 1 Packet 2 Packet 2 Packet 2 Packet 3 Packet 3 Packet 3 Timing of Datagram Packet Switching Host Host Node Node 1 2 3 4 Transmissiondelay ECE 1545

  7. A.1 A.1 C.1 C.2 A.2 A.2 C.1 A.3 A.3 A.1 A.2 A.3 A.1 A.1 C.1 A.2 C.2 C.2 A.3 A.3 A.1 C.2 C.1 A.3 C.1 C.2 A.2 A.1 C.2 A.3 A.1 A.2 A.3 A.2 A.2 A.2 A.2 A.2 Datagram Packet Switching A.2 ECE 1545

  8. VC Establishment Pkt1 Pkt1 Pkt1 Pkt2 Pkt2 Pkt2 Pkt3 Pkt3 Pkt3 VC Termination Timing of VC Packet Switching Host Host Node Node 1 2 3 4 Transmissiondelay ECE 1545

  9. A.1 A.2 A.3 VC 2 C.2 C.2 C.2 C.1 C.1 C.1 VC 1 A.1 A.1 A.1 A.1 A.1 A.1 C.1 C.1 A.2 A.2 A.2 A.2 C.2 C.2 A.3 A.3 A.3 A.3 A.3 A.3 C.1 C.1 A.1 A.1 C.2 C.2 A.2 A.2 A.3 A.3 A.1 A.1 A.1 A.1 A.2 A.2 A.2 A.2 A.3 A.3 A.3 A.3 Virtual-Circuit Packet Switching ECE 1545

  10. Packet Switching Technologies • Both packet switching technologies are used today: • Datagram packet switching: • IP routers (Internet) • Ethernet Switches (Switched LANs) • Virtual-circuit packet switching • Asynchronous Transfer Mode (ATM) • Multi-protocol label switching (MPLS) ECE 1545

  11. Packet Switch Architectures ECE 1545

  12. Packet Switches • Different types of packet switches: • IP routers • ATM switches • MPLS switches • Ethernet (LAN) switches • Frame Relay • All types of packet switches have very similar characteristics ECE 1545

  13. Hardware components of a router: Network interfaces Interconnection network Processor with a memory and CPU Switch Components ECE 1545

  14. Basic Architectural ComponentsPer-packet processing Output Scheduling Routing Table Switch Fabric Routing Decision Routing Table Forwarding Decision Routing Table Forwarding Decision

  15. Functional Components Control Datapath: per-packet processing ECE 1545

  16. Routing and Forwarding Routing functions include: • route calculation • maintenance of the routing table • execution of routing protocols Forwarding is per-packet processing • On high-end packet switches routers, forwarding is highly parallelized, and most work is done on the interface cards ECE 1545

  17. IP Router • Lookup packet destination address in forwarding table. • If known, forward to correct port. • If unknown, drop packet. • Decrement TTL, update header checksum. • Forward packet to outgoing interface. • Transmit packet onto link. ECE 1545

  18. ATM Switch • Look up VCI/VPI of cell in VC table. • Replace old VCI/VPI with new. • Forward cell to outgoing interface. • Transmit cell onto link. ECE 1545

  19. Ethernet Switch • Lookup frame destination address in forwarding table. • If known, forward to correct port. • If unknown, broadcast to all ports. • Learn source address of incoming frame. • Forward frame to outgoing interface. • Transmit frame onto link. ECE 1545

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