QoS research in a complicated world

Christian HuitemaArchitect Windows Networking & CommunicationsMicrosoft Corporation

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The state of research ?

•We need QoS for VoIP, video on demand, etc.

•To implement QoS, we need queuing models, signaling protocols, QoS contracts, etc.

•And I get to do tons of maths and publish papers.

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The contrarian's view

•Look at the real network!

•We don’t really need QoS for VoIP, we need bandwidth for video on demand, etc.

•QoS signaling is dead.

•Maths are nice, use them for adaptivity.

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Myth : QoS provides better service

Myth: In a QoS enabled network, you get

more bandwidth, less delays

Reality: QoS = access control. You can only provide better service to

some if you exclude others.

Deployment issue: Only develop an application, if there

is enough bandwidth “in most places”

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Myth: Applications will require QoS

Myth: Applications will use a QoS API,

because that will give better service.

Reality As long as QoS is not ubiquitous,

applications must be adaptive.

Deployment issue Since applications don’t require it, little

incentive to upgrade the network. Little incentive to maintain the API

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Myth: congestion occurs in the network

Myth: There are bottlenecks in the network,

each hop adds delays

Reality: Look at Global Crossing, Qwest,

Worldcom Price of Mbps divided by 6 in 2 years Congestion occurs mostly at the edges.

Deployment issue: Operators of large networks don’t

perceive any benefit to QoS, just costs.

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Myth: QoS mechanism provide quality

Myth: We can use QoS mechanisms to

protect users from network issues

Reality: How exactly do we use QoS to protect

a web server against a denial of service attack?

Deployment issue: Making the network more robust

requires “last mile” solutions.

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Myth: eventually, QoS everywhere

Myth: Eventually, all routers will provide QoS

Reality: “Wireless guarantee” is an oxymoron

Deployment issue: A broken QoS promise will break the

application. If you cannot have QoS everywhere,

the application must be adaptive

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A short summary

The difference between theory and practice is even larger in practice than in theory

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Three QoS research suggestions

Apply local solutions to local problemsGet more dataIf you don’t have guarantee, adapt!

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Suggestion: research edge solutions

Backbone = large, edge = small The law of big numbers does not apply

to small numbers

Edge = degrees of liberty for innovation MAC layer for wireless (802.1p ?) Cooperation between local players Receive side enforcement First router solutions…

Liberty => research playground

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Suggestion: get as much data as we can!

Understand delays and losses In the network, at the edges What is the distribution? What are the causes?

Fix the obvious bugs! E.g. router hiccups, bad hardware

Repeat the measurements Don’t settle for yesteryear data. History matters! Praise the XVI century astronomers!

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Suggestion: research adaptation models

Today’s model are very crude The 1988 Internet 6 nodes NS

simulations…

TCP slow-start is probably wrongIf we learn about the network, we can design better adaptation models

APP

APP

Need the right black box model

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A short summary

•Success is, finding something your professors don’t know

•Even better, prove them wrong

•Learn how the Internet really behaves,

•Find where the old hypotheses are wrong,

•Build on it!