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Routing vs. Switching

Routing vs. Switching. S. Keshav Cornell University IEEE INFOCOM ‘97. Router look up destination port based on destination address send variable length packet to destination port RSVP signaling for establishing QoS state for scheduling schedule variable length packet. Switch

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Routing vs. Switching

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  1. Routing vs. Switching S. Keshav Cornell University IEEE INFOCOM ‘97

  2. Router look up destination port based on destination address send variable length packet to destination port RSVP signaling for establishing QoS state for scheduling schedule variable length packet Switch look up destination port based on VCI send fixed length packet to destination port UNI signaling to establish QoS state for scheduling schedule fixed length packet What’s the difference?

  3. Four differences • Lookup • Data movement: fixed vs. variable length • Signaling: RSVP vs. UNI • Scheduling: fixed vs. variable length • Differences are rapidly disappearing

  4. Lookup • VCI lookup was much faster and cheaper • Not any more! • Several fast lookup schemes are known • (all are probably being patented!)

  5. Switching • Variable size is harder to switch • But we can segment and reassemble within a router • Or shared memory allows fixed-size headers to be switched

  6. Signaling • Both UNI and RSVP are complex • Timers make tuning and debugging hard • UNI 4.0 and RSVP are converging

  7. Scheduling • FIFO is easy for both • More complicated scheduling (such as FQ) is harder with variable size packets • but ASICs solve the problem • may need them anyway even with ATM • Large packets cause jitter in slow lines • not a problem with non-interactive apps or faster trunks

  8. Bottom line • Technical reasons to prefer ATM switching are fading fast • IP has a greater established base • Is it time to bury ATM?

  9. Another grave problem • Do we really need QoS in the network? • Big and dumb may be the answer • A rising tide raises all ships

  10. Research agenda • Fast IP routers • Retrofit a smidgeon of QoS • Capacity planning • Pricing • (Lightweight signaling)

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