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QoS Not Needed

QoS Not Needed. Ben Teitelbaum Internet2 VoIP SIG September, 2006. Outline. QoS dreams Mechanisms Problems Theoretic Practical Economic Alternatives Non-History Non-Future.

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QoS Not Needed

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  1. QoS Not Needed Ben TeitelbaumInternet2 VoIP SIGSeptember, 2006

  2. Outline • QoS dreams • Mechanisms • Problems • Theoretic • Practical • Economic • Alternatives • Non-History • Non-Future

  3. The Holy Grail of computer networking is to design a network that has the flexibility and low cost of the Internet, yet offers the end-to-end quality-of-service guarantees of the telephone network. - S. Keshav

  4. What QoS Is Not • It is not a synonym for “good performance” • It is not about local rationing • E.g. Packeteer, Vonage ATA • And, in this talk, is not taken to include non-elevated services • E.g. ABE, QBone Scavenger

  5. What QoS Is • Differentiated network service to provide better-than-default (BE) service • WLOG, assume hereafter a Van Jacobson, virtual leased line, Premium Service • Note that QoS is about removing only one factor that can cause a networked transaction to fail

  6. Mechanisms: Classification Policing Classification Queuing / AQM ?

  7. Mechanisms: Policing Policing Classification Queuing / AQM

  8. Mechanisms: Queuing / AQM Policing Classification Queuing / AQM

  9. Some Problems with QoS • Theoretic • Practical • Economic

  10. Theoretic Problems CampusA • How do edge-to-edge “virtual trunks” concatenate to form an e2e service? GigaPoPA CampusB Backbone Campus C GigaPoPB • What exactly are the policers and shapers at inter-domain boundaries? CampusD

  11. Practical Problems • Requires all-or-nothing network upgrades (e.g. all access interfaces must police) • Dramatic changes to network operations, peering arrangements, and business models

  12. Practical Problems (cont.) • In a well-provisioned network Premium is indistinguishable from BE • How can a user (or even a provider) verify service? • What happens to Premium service in the face of a determined adversary?

  13. Economic Problems • Router costs • Operational costs • Billing costs • Support costs

  14. Some Alternatives to QoS • Overprovisioning • Cheapest way to provide fabulous service to important apps, is to provide it to all apps • Pricing • Congestion pricing • Nice theoretic properties • But not practical • Usage-based pricing • Would help a lot • Business access is increasingly metered • Could provide differentiated services (e.g. Paris Metro Pricing)

  15. A History of Non-Deployment • QoS Wasn’t Needed (1997-2001) • QoS Isn’t Needed (2002-2006) • QoS Shouldn’t Be Needed (2007-)

  16. QoS Wasn’t Needed (1997-2001) • Ambitious QoS program (QBone) • Many hard-won lessons • Negative outcome not at all a foregone conclusion • Naïve codecs ported from ISDN world wouldn’t tolerate packet loss • Few users of real-time applications anyway

  17. QoS Isn’t Needed (2002-2006) • Adaptive, loss-tolerant codecs • Many users of real-time applications (Vonage, Skype, Internet2 videoconf) • Generous provisioning ensures that real-time apps just work

  18. Hang On a Second! • ~104 hosts with nothing slower than switched 100Mbps Ethernet between them • ~25 of these could congest the 2.4 Gbps Abilene backbone (or 100 the 10 Gbps) • 90% of traffic is TCP • TCP is designed to congest • Yet, the backbone is lightly loaded • What’s going on?!

  19. The Terrible Truth (overprovisioning works, because TCP doesn’t) http://netflow.internet2.edu/weekly/20060501/

  20. QoS Shouldn’t Be Needed (2007-) • Either TCP will stay broken or be replaced • New transport protocols (e.g. XCP, MaxNet, PCP) don’t build huge queues • Even better packet loss concealment through improved codecs

  21. Summary • QoS is interesting • QoS is expensive • Scarcity should become scarcer • QoS has not been needed thus far • QoS should not be needed for the foreseeable future

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