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If we started again, would we still use packet switching?

If we started again, would we still use packet switching?. Nick McKeown Stanford University nickm@stanford.edu. Why does the Internet use packet switching?. Efficient use of expensive links:

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If we started again, would we still use packet switching?

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  1. If we started again, would we still use packet switching? Nick McKeown Stanford University nickm@stanford.edu

  2. Why does the Internet usepacket switching? • Efficient use of expensive links: “Circuit switching is rarely used for data networks, ... because of very inefficient use of the links” - Gallager • 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 Source: Networking 101

  3. Statistical Multiplexing A rate x x A time B rate x x B time

  4. Statistical Multiplexing A+B rate 2x C < 2x A C B time

  5. Neither reason is true today Link capacity is abundant and under used • Most links are unused due to lack of switching capacity. • Most links are utilized < 10%, and utilization is going down over time. Routers rarely fail • They are designed for <5s down-time per year. • They take >30s to recover when they do (circuit switches are required to recover in <50ms).

  6. Myth: Packet switching is simpler • A typical Internet router contains over 500M gates, 32 CPUs and 10Gbytes of memory. Cf: A circuit switch of the same generation could run ten times faster with 1/10th the gates and no memory.

  7. What dictates the Internet’s performance Processing power Link speed

  8. Fast Links, Slow Routers Processing Power Link Speed (Fiber) Source: SPEC95Int & David Miller, Stanford.

  9. Fast Links, Slow Routers Processing Power Link Speed (Fiber) 10000 1000 2x / 2 years 2x / 7 months 100 Fiber Capacity (Gbit/s) 10 1 1985 1990 1995 2000 0,1 TDM DWDM Source: SPEC95Int & David Miller, Stanford.

  10. What will happen: (fewer features) Or perhaps we’re doing something wrong? Packet Switch Capacity What we’d like: (more features) QoS, Multicast, Security, … Instructions per arriving byte time

  11. Myth: Future routers will be all optical • Packet switches require buffering. • 2. We cannot buffer light.

  12. So it’s not surprising that it already is mostly circuit switched.

  13. How we think the Internet is

  14. How the Internet really is $35Bn $6Bn Packet Switched (IP routers) Circuit Switched (SONET)

  15. How the Internet really is Your Local CO IP routers Your Local CO IP routers SONET/SDH

  16. We use the Internet as if it were circuit switched Response Time Client A R1 R2 R3 Server B

  17. 100 clients 1 server 1 Mb/s File = 1Mbit 99% of Circuits Finish Earlier An Example

  18. Could the Internet be circuit switched? • Very simple circuit switches could establish a circuit for each file transfer • Simple, low-cost and very fast hardware • Requires no buffering • QoS is much simpler • Fits nicely with optical technology • Main problem: granularity of flows • Mismatch between user and WDM

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