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Circuit switching in the Internet

Circuit switching in the Internet. Ph.D. oral examination Pablo Molinero-Fern á ndez 21 st May 2002. GAP OF 5x!!. Traffic doubles every year. Cost and complexity of five times as many central offices is prohibitive. Optics removes bandwidth constraints. But we cannot buffer light!.

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Circuit switching in the Internet

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  1. Circuit switching in the Internet Ph.D. oral examination Pablo Molinero-Fernández 21st May 2002

  2. GAP OF 5x!! Traffic doubles every year Cost and complexity of five times as many central offices is prohibitive

  3. Optics removes bandwidth constraints But we cannot buffer light!

  4. Circuit switching • Link bandwidth is reserved • Need signaling • No buffering • No processing in data path

  5. Packet switching • Link bandwidth is shared • Buffering • Per-packet processing

  6. Contributions The Internet needs circuit switching in the core TCP Switching: how to integrate circuit switching in the core Provisioning of fat pipes in an all-optical backbone

  7. How we think the Internet is

  8. Why the Internet usespacket switching • Efficient use of expensive links: • “Circuit switching is rarely used for data networks, ... because of very inefficient use of the links” – Bertsekas & Gallager ‘92 • Resilience to failure of links & routers: • ”For high reliability, ... [the Internet] was to be a datagram subnet, so if some lines and [routers] were destroyed, messages could be ... rerouted” – Tanenbaum ‘96

  9. What the Internet is really like today SONET/SDH DWDM

  10. What the Internet is really like today Modems, DSL

  11. Performance criteria Users • Response time • Service Level Agreement (QoS) Carriers • Cost: Bandwidth efficiency • Reliability and stability • Low complexity

  12. What users want Users • Response time • Service Level Agreement (QoS) Carriers • Cost: Bandwidth efficiency • Reliability and stability • Low complexity

  13. 100 clients 1 server 1 Gb/s Circuit sw Packet sw All but one of circuits finish earlier Flow bandwidth 1 Gb/s 10 Mb/s Avg response time 0.51 s 1 s Max response time 1 s 1 s Response time of packets and circuits File = 10Mbit x 100

  14. 100 clients 1 server 1 Gb/s Circuit sw Packet sw A big flow can kill CS if it blocks the link Flow bandwidth 1 Gb/s 10Mb/s;1Gb/s Avg response time 10.50 s 1.10 sec Max response time 10.99 s 10.99 sec Response time when blocking occurs File = 10Gbit/ 10Mbit x 99

  15. 100 clients 1 server 1 Gb/s 1 Mb/s No difference between CS and PS in core Circuit sw Packet sw Flow bandwidth 1 Mb/s 1 Mb/s Avg response time 109.9s 109.9sec Max response time 10,000 s 10,000 sec Response time with flow rate limits File = 10Gbit/ 10Mbit x 99

  16. Analytical modeling • Fluid model: • Many independent arrivals => Poisson • Service policies: • Packets: Processor Sharing • Circuits: FCFS • Service time distribution: • Flow size variance: Bimodal • Realistic flow size distrib: Pareto

  17. + Flow size variance Fluid model: M/BiModal/N • Access link is as fast as the core link • Hogging by long flows

  18. + Flow size variance Fluid model: M/BiModal/N • Flow rate limited by access link (1/N) • Same response time regardless of flow size variance, if N is large N=2k

  19. Fluid model: M/Pareto/N Link hogging becomes very bad with heavy-tailed traffic, if ratio N=1

  20. 512 Fluid model: M/Pareto/N • Response time similar to IP if core/access ratio N is large • Typically N >> 1,000 N =2k

  21. Users see little difference in response time • Simulation of full networks • N is large => same response time Circuit switching Packet switching

  22. Service Level Agreements • Packet switching: • Algorithms (WFQ, DRR, …) => not used • Thus we must overprovisioning => used and it works • Circuit switching: • Simple QoS: guaranteed BW => no jitter

  23. What carriers want Users • Response time • Service Level Agreement (QoS) Carriers • Cost: Bandwidth efficiency • Reliability and stability • Low complexity

  24. Cost: Bandwidth efficiency • Argument: packets share all link BW => statistical multiplexing gain => more throughput with bursty traffic • Reality: • Internet avg. link utilization: 5-20% [Coffman&Odlyzko’02] • Phone avg. link utilization: ~33% [Odlyzko’99] • There is a glut of BW in the core [WSJ’00] • Result: • Packets more efficient, but BW is no longer a scarce resource

  25. OC-48 OC-3 OC-12 Carriers peak allocate their network • When over-provisioning, link BW is virtually peak allocated • That is exactly what circuit switching does Source: Chuck Fraleigh ‘02

  26. Reliability and stability (I) • Argument: because of the state, rerouting a circuit is more costly than with packets • Reality: • Internet average availability: 1220 min/year down time [Labovitz’99] • Phone average availability: 5 min/year down time [Kuhn’97]

  27. Reliability and stability (II) • Reality (cont.): • IP recovers in about 3 min (median), sometimes it takes over 15 min [Labovitz’01] • SONET required to recover in less than 50 ms • Result: • No evidence packet switching is more robust

  28. Low complexity (I) • Argument: No per-flow state => packet switching is simpler • Reality: • PS: 8M lines of code in core router [Cisco’s IOS ‘00] • CS: 18M lines of code in telephone switch [AT&T/Lucent 5ESS ‘96] • CS: 3M lines of code in transport switch [’01] • Result: • Packet switching does not seem inherently less complex than circuit switching

  29. Interconnect Egress linecard Ingress linecard Route lookup Buffer ing Framing TTL process ing Framing Buffer ing QoS schedul ing Interconnect scheduling Control plane Control path Data path Scheduling path Functions in a packet switch

  30. Ingress linecard Egress linecard Interconnect Framing Framing Interconnect scheduling Control plane Control path Data path Functions in a circuit switch

  31. Low complexity (II) • Argument: IP does not have the signaling of circuits switches => Routers go faster • Reality: • IP does almost same operations on every packet as a circuit switch on the circuit establishment • CS has no work to do once circuit is established • Result: • The fastest commercially-available circuit switches [Ciena ’01, Lucent ‘01] have 5x the capacity of the fastest routers [Cisco ’01, Juniper ’02]

  32. Network architecture • Use packet switching • Better response time (ratio N small) • Efficient use of the spectrum LANs & wireless • If metro-to-access BW ratio (N) is small => use packets • Otherwise use what costs less MANs • Use circuit switching • More capacity, reliability • Similar response time & QoS WANs

  33. Contributions The Internet needs circuit switching in the core TCP Switching: how to integrate circuit switching in the core Provisioning of fat pipes in an all-optical backbone

  34. Integration of circuits and packets • Create a separate circuit for each user flow • IP controls circuits • Optimize for the most common case • TCP (90-95% of traffic) • Data (9 out of 10 pkts) TCP Switching

  35. TCP Switching exposes circuits to IP IP routers TCP Switches

  36. Destina-tion Source Router Router Router SYN SYN+ACK DATA Packets Packets Packets Packets TCP “creates” a connection

  37. Boundary TCP-SW Core TCP-SW Boundary TCP-SW Destina-tion Source SYN Create circuit SYN+ACK Create circuit DATA Packets One Circuit Packets Let TCP leave state behind

  38. What is a typical flow? • Most traffic are TCP connections: • Taking less than 10 s, 12 packets and 4 KBytes • Obtaining less than 100 Kbps • ~40% of the flows continue transmitting ACKs after sending a FIN (asymmetrical closures)

  39. State management feasibility • Amount of state • Minimum circuit = 56 Kb/s. • 178,000 circuits for OC-192. • Update rate • About 51,000 entries per sec for OC-192 • Implementable in hardware or software.

  40. TCP Switching can be implemented in software TCP Switching boundary router: • Kernel module in Linux 2.4 1GHz PC • Forwarding latency • Forward one packet: 21ms. • Compare to: 17ms for IP. • Compare to: 95ms for IP + QoS. • Time to create new circuit: 57ms. Source: Byung-Gon Chun ‘01

  41. Slow Start Congestion Avoidance Instantaneous bandwidth Circuit BW time Flow duration Inactivity timeout Bandwidth inefficiencies Compromise: inactivity timeout of few seconds

  42. Related work • IP Switching • Uses ATM virtual circuits (i.e. packets) • Became MPLS (but no longer user flows) • Generalized Multi-Protocol Label Switching (GMPLS) • Coarse circuits • Heavy weight signaling

  43. Contributions The Internet needs circuit switching in the core TCP Switching: how to integrate circuit switching in the core Provisioning of fat pipes in an all-optical backbone

  44. New networking scenario IP routers Optical Switches

  45. New networking scenario IP Linecards Optical Crossconnect

  46. Circuit creation is slow • We need a safeguard to avoid running out of BW => inefficiency A slow signaling requires a larger BW safeguard

  47. Controlling coarse circuits with user flows • Should use the fastest optical switching elements • Should avoid ACKs => no RTT

  48. Conclusions • Circuits should be used in the core, packets in the edges • TCP Switching integrates circuits and packets in an evolutionary way • User flows can be used to control an all-optical network

  49. Papers • PMF, Nick McKeown, "TCP Switching: Exposing Circuits to IP“, IEEE Micro, 2002 • PMF, NM, "TCP Switching: Exposing Circuits to IP“, Hot Interconnects, 2001 • PMF, NM, “Study of routing behavior trough traffic analysis and traceroute measurements”, NAT Times, 2001 • PMF, NM, Hui Zhang, "Is IP going to take over the world (of communications)?“, submitted

  50. Thank you

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