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

Delve into the use of packet switching in the Internet, exploring its efficiency, resilience, and the evolving landscape of network technologies. Uncover myths, realities, and potential future directions for improving performance and features.

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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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