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ELEN 602 Lecture 18

ELEN 602 Lecture 18

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ELEN 602 Lecture 18

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  1. Packet switches Traffic Management ELEN 602 Lecture 18

  2. Gateway Organization Servers To internet or wide area network s s Backbone R R R S Departmental Server S S R R R s s s s s s s s s Campus Network

  3. Intradomain and Interdomain levels Interdomain level Border routers Internet service provider Autonomous system or domain Border routers LAN level Intradomain level

  4. National service provider A (a) National service provider B NAP NAP National service provider C (b) NAP RA RB Route server LAN RC

  5. Components of Generic Switch/Router Control 1 Line Card Line Card 1 2 2 Line Card Line Card Interconnection Fabric 3 3 Line Card Line Card … … … … N N Line Card Line Card

  6. 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 Buffering

  7. Crossbar Switches

  8. Workstation based Router CPU I/O Bus 1 NIC Card 2 NIC Card NIC Card 3 Main Memory … … N NIC Card

  9. 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 I/O bus CPU Interface 1 Interface 2 Interface 3 Main memory Workstation-Based • 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

  10. 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 log2n Self-Routing Fabrics

  11. 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 High-Speed IP Router

  12. 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

  13. Virtual-circuit Packet Switching Packet Packet

  14. Delays in virtual-circuit switching t Connect request 1 3 2 CC t Release 3 CR 1 2 CC t Connect confirm 1 2 CR 3 t Figure 7.19

  15. Signaling for virtual-circuit setup Connect request Connect request Connect request SW 1 SW n SW 2 … Connect confirm Connect confirm

  16. Example virtual-circuit routing table Output port Next identifier Identifier 12 44 13 Entry for packets with identifier 15 15 15 23 27 13 16 58 7 34

  17. FIFO Queuing: (a) Packet buffer Arriving packets Transmission link Packet discard when full FIFO Queuing with discard priority (b) Packet buffer Arriving packets Transmission link Class 1 discard when full Class 2 discard when threshold exceeded

  18. HOL Priority queuing Packet discard when full High-priority packets Transmission link Low-priority packets When high-priority queue empty Packet discard when full

  19. Sorting packets according to priority tag Sorted packet buffer Arriving packets Tagging unit Transmission link Packet discard when full

  20. Fair queuing Approximated bit-level round robin service Packet flow 1 Packet flow 2 C bits/second Transmission link Packet flow n

  21. Fluid-flow and packet-by-packet FQ Queue 1 @ t=0 Fluid-flow system: both packets served at rate 1/2 1 Queue 2 @ t=0 Both packets complete service at t=2 t 0 2 1 Packet from queue 2 waiting Packet-by-packet system: queue 1 served first at rate 1; then queue 2 served at rate 1. 1 Packet from queue 2 being served Packet from queue 1 being served t 0 2 1

  22. Rounds Computing finishing times Generalize so R(t) is continuous, not discrete R(t) grows at rate inversely proportional to nactive(t)

  23. 2 Fluid-flow system: both packets served at rate 1/2 Queue 1 @ t=0 1 Queue 2 @ t=0 Packet from queue s served at rate 1 t 0 2 3 Packet-by-packet fair queueing: queue 2 served at rate 1 Packet from queue 2 waiting 1 Packet from queue 1 being served at rate 1 t 2 1 3 0 Fluid-flow and packet-by-packet FQ

  24. Queue 1 @ t=0 Fluid-flow system: packet from queue 1 served at rate 1/4; Packet from queue 1 served at rate 1 Queue 2 @ t=0 1 Packet from queue 2 served at rate 3/4 t 0 2 1 Packet from queue 1 waiting Packet-by-packet weighted fair queueing: queue 2 served first at rate 1; then queue 1 served at rate 1. 1 Packet from queue 1 being served Packet from queue 2 being served t 0 2 1 Weighted Fair Queuing