1. 1 ELEN 602 Lecture 18 Packet switches Traffic Management

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

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

4. 4 RARA RBRB RCRC Route server NAP National service provider A National service provider B National service provider C LAN NAP (a) (b)

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

6. 6 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

7. 7 Crossbar Switches

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

9. 9 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 CPU Main memory I/O bus Interface 1 Interface 2 Interface 3 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. 10 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 log 2 n

11. 11 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

12. 12 High-Speed Router Line card (forwarding buffering) Line card (forwarding buffering) Line card (forwarding buffering) Line card (forwarding buffering) Routing CPU Buffer memory Routing software w/ router OS Routing software w/ router OS

13. 13 Packet Virtual-circuit Packet Switching

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

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

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

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

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

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

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

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

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

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

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