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Packet switches Traffic Management. ELEN 602 Lecture 18. 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.
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Packet switches Traffic Management ELEN 602 Lecture 18
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
Intradomain and Interdomain levels Interdomain level Border routers Internet service provider Autonomous system or domain Border routers LAN level Intradomain level
National service provider A (a) National service provider B NAP NAP National service provider C (b) NAP RA RB Route server LAN RC
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
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
Workstation based Router CPU I/O Bus 1 NIC Card 2 NIC Card NIC Card 3 Main Memory … … N NIC Card
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
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
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
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
Virtual-circuit Packet Switching Packet Packet
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
Signaling for virtual-circuit setup Connect request Connect request Connect request SW 1 SW n SW 2 … Connect confirm Connect confirm
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
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
HOL Priority queuing Packet discard when full High-priority packets Transmission link Low-priority packets When high-priority queue empty Packet discard when full
Sorting packets according to priority tag Sorted packet buffer Arriving packets Tagging unit Transmission link Packet discard when full
Fair queuing Approximated bit-level round robin service Packet flow 1 Packet flow 2 C bits/second Transmission link Packet flow n
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
Rounds Computing finishing times Generalize so R(t) is continuous, not discrete R(t) grows at rate inversely proportional to nactive(t)
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
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