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Router Construction

Router Construction. Outline Switched Fabrics IP Routers Extensible (Active) Routers. I/O bus. CPU. Interface 1. Interface 2. Interface 3. Main memory. Workstation-Based. Aggregate bandwidth 1/2 of the I/O bus bandwidth capacity shared among all hosts connected to switch

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Router Construction

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  1. Router Construction • Outline • Switched Fabrics • IP Routers • Extensible (Active) Routers 4/598N: Computer Networks

  2. I/O bus CPU Interface 1 Interface 2 Interface 3 Main memory Workstation-Based • Aggregate bandwidth • 1/2 of the I/O bus bandwidth • capacity shared among all hosts connected to switch • example: 800Mbps bus can support 8 T3 ports • Packets-per-second • must be able to switch small packets • 100,000 packets-per-second is achievable • e.g., 64-byte packets implies 51.2Mbps 4/598N: Computer Networks

  3. Input Output port port Output Input port port Fabric Output Input port port Output Input port port Switching Hardware • Design Goals • throughput (depends on traffic model) • scalability (a function of n) • Ports • circuit management (e.g., map VCIs, route datagrams) • buffering (input and/or output) • Fabric • as simple as possible • sometimes do buffering (internal) 4/598N: Computer Networks

  4. Buffering • Wherever contention is possible • input port (contend for fabric) • internal (contend for output port) • output port (contend for link) • Head-of-Line Blocking • input buffering 4/598N: Computer Networks

  5. Crossbar Switches 4/598N: Computer Networks

  6. Inputs D D D D D D D D D D D D D D 1 2 3 4 Outputs Knockout Switch • Example crossbar • Concentrator • select l of n packets • Complexity: n2 4/598N: Computer Networks

  7. Shifter (a) Buffers Shifter (b) Buffers Shifter (c) Buffers Knockout Switch (cont) • Output Buffer 4/598N: Computer Networks

  8. Self-Routing Fabrics • Banyan Network • constructed from simple 2 x 2 switching elements • self-routing header attached to each packet • elements arranged to route based on this header • no collisions if input packets sorted into ascending order • complexity: n log2 n 4/598N: Computer Networks

  9. Self-Routing Fabrics (cont) • Batcher Network • switching elements sort two numbers • some elements sort into ascending (clear) • some elements sort into descending (shaded) • elements arranged to implement merge sort • complexity: n log22 n • Common Design: Batcher-Banyan Switch 4/598N: Computer Networks

  10. High-Speed IP Router • Switch (possibly ATM) • Line Cards + Forwarding Engines • link interface • router lookup (input) • common IP path (input) • packet queue (output) • Network Processor • routing protocol(s) • exceptional cases 4/598N: Computer Networks

  11. Routing software w/ router OS Line card (forwarding buffering) Routing CPU Buffer memory Line card (forwarding buffering) Line card (forwarding buffering) Line card (forwarding buffering) High-Speed Router 4/598N: Computer Networks

  12. PC PC PC PC PC PC NI with uP NI with uP NI with uP NI with uP NI with uP NI with uP CPU CPU CPU CPU CPU CPU . . . . . . . . . . . . . . . . . . MEM MEM MEM MEM MEM MEM NI with uP NI with uP NI with uP NI with uP NI with uP NI with uP Crossbar Switch Alternative Design 4/598N: Computer Networks

  13. Recap First mile problem Internet Sprint Charter www.yahoo.com End Users UUNET MCI www.cnn.com Last mile problem 4/598N: Computer Networks

  14. Recap • Direct link networks • Packet switching 4/598N: Computer Networks

  15. Internetworking 4/598N: Computer Networks

  16. Internetworking • Outline • Best Effort Service Model • Global Addressing Scheme 4/598N: Computer Networks

  17. Network 1 (Ethernet) H7 R3 H8 H2 H1 H3 Network 4 (point-to-point) Network 2 (Ethernet) R1 R2 H4 Network 3 (FDDI) H5 H6 IP Internet • Concatenation of Networks • Protocol Stack H1 H8 TCP TCP R1 R2 R3 IP IP IP IP IP FDDI PPP ETH ETH ETH FDDI PPP ETH 4/598N: Computer Networks

  18. 0 4 8 16 19 31 TOS Length V ersion HLen Ident Flags Offset TTL Protocol Checksum SourceAddr DestinationAddr Pad Options (variable) (variable) Data 1. Service Model • Connectionless (datagram-based) • Best-effort delivery (unreliable service) • packets are lost • packets are delivered out of order • duplicate copies of a packet are delivered • packets can be delayed for a long time • Datagram format 4/598N: Computer Networks

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