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QoS Not Needed

Explore the theoretical, practical, and economic aspects of Quality of Service (QoS) in computer networking with insights on mechanisms, problems, and alternatives. Understand why QoS may not be needed in the evolving landscape of network services.

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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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