peter key [email protected] service differentiation: congestion pricing, brokers and bandwidth...
TRANSCRIPT
Peter KeyPeter Key
[email protected]@microsoft.comhttp://research.microsoft.com/network/disgame.htmhttp://research.microsoft.com/network/disgame.htm
Service Differentiation: Congestion Pricing, Brokers and
Bandwidth Futures
Sine qua non ...
Differential Services / Differential Services / QOS QOS Differential Differential pricing!pricing!
Outline
BackgroundBackground Congestion PricingCongestion Pricing A game ….A game …. Commodity markets and FuturesCommodity markets and Futures
Access to / Control of Scarce Resources Airline seats, electrical power, economic Airline seats, electrical power, economic
wealthwealth Are networks any different?Are networks any different? Control technologies not independent or Control technologies not independent or
implementation /economicsimplementation /economics ATM: eg sensible relative tariffs, ATM: eg sensible relative tariffs,
CBR 1, VBR 2, ABR .1, UBR .01, … CBR 1, VBR 2, ABR .1, UBR .01, … result?result?
Resource system (‘network’)
Resource j
Capacity Cj
User /route r Ajr links users to resources
Freebyte
The network is free most of the time!The network is free most of the time! Only pay when busy (incremental cost, Only pay when busy (incremental cost,
small)small) … … aka Congestion Pricingaka Congestion Pricing
Send a signal to users when traffic that Send a signal to users when traffic that should not be carried enters (moveable should not be carried enters (moveable threshold)threshold)
Basic Idea
Users generate load (packets)Users generate load (packets) Network sends back signals (load dependent)Network sends back signals (load dependent) Signals : proportional to loadSignals : proportional to load
Act as feedback indicatorsAct as feedback indicators Represent pricing signalsRepresent pricing signals
marginal incremental costs (derivatives …)marginal incremental costs (derivatives …)congestion costscongestion costsreal money or virtual / distributed mintreal money or virtual / distributed mint
Matching Prices to Load
TheoremTheorem: : For linear increase multiplicative For linear increase multiplicative feedback flow control family, cannot have demand feedback flow control family, cannot have demand =capacity if prices are bounded for fixed capacity =capacity if prices are bounded for fixed capacity and arbitrary number number of flows.and arbitrary number number of flows.
IfIf prices are unbounded (bad!) then can have demand prices are unbounded (bad!) then can have demand capacity as number of flows increase, capacity as number of flows increase,
ElseElse: Match willingness to pay to price capacity: Match willingness to pay to price capacity
Sample Path Shadow Prices
C
1 2 3 4 5 6 7 8 9 10
Time
Capacity
pktsC slotted time
Shadow path shadow prices -buffered model
Time
Bu
ffer
Co
nte
nt
B
B
Pkts
Optimisation Framework (for fairness)
System optimum
rr txxUMax User optimum
rr
jr
jj
rr
xAy
yCxUMax
U C is cost function,eg
C y Cj j c h
Consistent set of taxes (prices) and load exist s.t. user opt = social opt.
unconstrainedjj
r r
dC
dy
U x t
Example - elastic control
tfwxx ttt 1
reflects willingness to pay, per unit time
is feedback received from the network tw
f t
if (resource/ bottleneck overloaded)
else 0tf t x
eg ,res on route
( )t t jj
f t x p load
Applications Virtual Private NetworksVirtual Private Networks Non-TCP appsNon-TCP apps
WebWeb MediaMedia
MBONE Tools, RealMedia, NetshowMBONE Tools, RealMedia, Netshow Real application uses (like a DB)Real application uses (like a DB)
Aggregates
All the channels in a VPN connectionAll the channels in a VPN connection Audio/Video/Data in a conferenceAudio/Video/Data in a conference ““Working set” for web serverWorking set” for web server Policy based routers/firewallsPolicy based routers/firewalls
Aggregates: Audio / Video
Policy
scheduler
NetworkUser/ end system
Network vs Users“My work is a game, a very serious game”
Escher
Users
Signals
Data/Info
Network
Flow Control and Marking Strategies
Definition: The phenotype of an individual plant or animal … or flow-control scheme … is a consequence of the interaction between its genotype and the environment in which it exists
Distributed Multi-player Game
Internet
MSRCambridge
Example Game
Transfer a given amount of data Transfer a given amount of data FF at at minimum cost in time minimum cost in time TT
Strategies:Strategies: CBR, CBR,
if stationary regime, optimal if price if stationary regime, optimal if price “convex” in region (lightly loaded)“convex” in region (lightly loaded)
else, have to predict fluctuations else, have to predict fluctuations
WTP vs TCP
The User interface …
Must be simple!
Guaranteed Flows / Streams?
Probabilistic guarantees OK, provided proportion Probabilistic guarantees OK, provided proportion of adaptive traffic adequateof adaptive traffic adequate
Just a question of risk - brokers (cf fixed rate Just a question of risk - brokers (cf fixed rate mortgages)mortgages)
Futures market:Futures market: a reservation is a (European) call option for a reservation is a (European) call option for
an amount of bandwidth, where fair price = an amount of bandwidth, where fair price = Integral of expected price over expected life-Integral of expected price over expected life-timetime
Bandwidth Exchanges
9 Inteconnection operators (clearing houses, 9 Inteconnection operators (clearing houses, brokers etc)brokers etc)
Band-X, London 1997 Band-X, London 1997 RateXchanges, anonymous,RateXchanges, anonymous,
PSTN voice, VOIP, b/widthPSTN voice, VOIP, b/width
Is Bandwidth Commodity?
commoditycommodity A physical substance, such as food, grains, and A physical substance, such as food, grains, and
metals, which is interchangeable with other metals, which is interchangeable with other product of the same type, and which investors product of the same type, and which investors buy or sell, usually through buy or sell, usually through futures contractsfutures contracts. . Or more generally, a product which Or more generally, a product which tradestrades on a on a commodity exchangecommodity exchange
Originally, basic, unrefined (wheat not flour)Originally, basic, unrefined (wheat not flour)
Commodity Markets
History repeats itself … (Fora Vendalia)History repeats itself … (Fora Vendalia) Japanese forward contract in 1730 for riceJapanese forward contract in 1730 for rice
In China 4000BC???In China 4000BC??? Chicago forwards 1833+, cash marketsChicago forwards 1833+, cash markets Standards (quality / quantity evolved …)Standards (quality / quantity evolved …) Options on futures, 1983Options on futures, 1983 Forward contracts aimed at delivery, now only a Forward contracts aimed at delivery, now only a
few % completefew % complete
Futures and Auctions
Market efficient? (Sorros ….)Market efficient? (Sorros ….) Commodity prices highly random (small Commodity prices highly random (small
trend) trend) Auctions: FCC holds b/width auctionsAuctions: FCC holds b/width auctions
Futures pricing
Assume current rate Assume current rate pptt
Fair price for European option at time Fair price for European option at time tt lasting expected time lasting expected time TT given current spot given current spot price s=price s=pp0, 0, (constant load) (constant load)
0
t T
t
t
E p p dt
Second Price Auctions
Suppose users are prepared to pay amount Suppose users are prepared to pay amount per packet, (eg fixed data, maximum cost), per packet, (eg fixed data, maximum cost), if price goes above this, will drop outif price goes above this, will drop out
In a mixed environment, those left pay this In a mixed environment, those left pay this clearing priceclearing price
ie Vickrey auction via congestion pricingie Vickrey auction via congestion pricing
TimescalesConnection
Reaction (RTT)
Packet Level
averagerate
Seconds
line rate
ms
s
Application Network
ms
s
Critical timescale
Critical timescales
Critical TimescalesThreshold Loading Leased line LAN Backbone
1 0.2 0.005 0 0.0000210 0.89 0.27 0.06 0.00145 0.984 5.1 1 0.017
180 0.997 81 17 0.27
Facilitators
Small buffers (compared to transmission Small buffers (compared to transmission delay)delay)
Target loads below 100% …Target loads below 100% … Simple feedback signal, eg ECN bit/byteSimple feedback signal, eg ECN bit/byte Signal reflects costs but …Signal reflects costs but … User interface simple (risk apportionment)User interface simple (risk apportionment)