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Transcript
ELEN 602 Lecture 18 • Packet switches • Traffic Management 1 Gateway Organization Servers To internet or wide area network s s Backbone R R R S Departmental Server R S S R R s s s s s s s s s Campus Network 2 Intradomain and Interdomain levels Interdomain level Border routers Internet service provider Autonomous system or domain Border routers LAN level Intradomain level 3 National service provider A (a) National service provider B NAP NAP National service provider C (b) NAP RA Route server RB LAN RC 4 Components of Generic Switch/Router Control Line Card … … N Line Card Line Card 1 2 Line Card 3 Line Card … 3 Line Card Line Card … Line Card Interconnection Fabric 1 2 N 5 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 2 1 2 Port 1 Sw itch Port 2 6 Crossbar Switches 7 Workstation based Router NIC Card 3 NIC Card N NIC Card … … 1 2 NIC Card CPU Main Memory I/O Bus 8 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-persecond is achievable – e.g., 64-byte packets implies 51.2Mbps I/O bus CPU Interface 1 Interface 2 Interface 3 Main memory 9 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 001 011 001 110 111 011 110 111 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 11 Line card (forwarding buffering) High-Speed Router Routing CPU Buffer memory Line card (forwarding buffering) Line card (forwarding buffering) Line card (forwarding buffering) Routing software w/ router OS 12 Virtual-circuit Packet Switching Packet Packet 13 Delays in virtual-circuit switching t Connect request CC CR CC CR Connect confirm 1 2 3 1 2 t Release 3 t 1 2 3 t 14 Signaling for virtual-circuit setup SW 1 Connect request Connect confirm SW 2 … Connect request SW n Connect request Connect confirm 15 Example virtual-circuit routing table Entry for packets with identifier 15 Identifier Output port Next identifier 12 13 44 15 15 23 27 13 16 58 7 34 16 FIFO Queuing: (a) Packet buffer Arriving packets Transmission link Packet discard when full FIFO Queuing with discard priority (b) Packet buffer Arriving packets Class 1 discard when full Transmission link Class 2 discard when threshold exceeded 17 HOL Priority queuing Packet discard when full High-priority packets Transmission link Low-priority packets When high-priority queue empty Packet discard when full 18 Sorting packets according to priority tag Arriving packets Sorted packet buffer Tagging unit Packet discard when full Transmission link 19 Fair queuing Packet flow 1 Packet flow 2 Approximated bit-level round robin service C bits/second Transmission link Packet flow n 20 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 t 0 1 Packet from queue 2 waiting Both packets complete service at t=2 2 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 1 2 21 Computing finishing times Rounds Generalize so R(t) is continuous, not discrete R(t) grows at rate inversely proportional to nactive(t) 22 2 Queue 1 @ t=0 Fluid-flow system: both packets served at rate 1/2 1 Queue 2 @ t=0 Packet from queue s served at rate 1 0 2 t 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 0 1 2 t 3 Fluid-flow and packet-by-packet FQ 23 Queue 1 @ t=0 Fluid-flow system: packet from queue 1 served at rate 1/4; Queue 2 @ t=0 1 Packet from queue 2 served at rate 3/4 Packet from queue 1 served at rate 1 t 0 1 Packet from queue 1 waiting 2 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 1 Weighted Fair Queuing 2 24