Bandwidth Allocation in Bandwidth Allocation in Sense-and-Respond Sense-and-Respond

SystemsSystems

Vincenzo LiberatoreVincenzo Liberatore

Research supported in part by NSF CCR-0329910, Department of CommerceTOP 39-60-04003, NASA NNC04AA12A, and an OhioICE training grant.

Sense-And-RespondSense-And-Respond

Computing in the Computing in the physical worldphysical world

ComponentsComponents Sensors, actuatorsSensors, actuators ControllersControllers NetworksNetworks

Sense-and-RespondSense-and-Respond

EnablesEnables Industrial automation [BIndustrial automation [BLL04]04] Distributed instrumentation [ACRKNDistributed instrumentation [ACRKNLL03]03] Unmanned vehicles [Unmanned vehicles [LLNB03]NB03] Home robotics [NNHome robotics [NNLL02]02] Distributed virtual environments [Distributed virtual environments [LLCCK05]CCK05] Power distribution [P05]Power distribution [P05] Building structure control [SLT05]Building structure control [SLT05]

Merge cyber- and physical- worldsMerge cyber- and physical- worlds Networked control and tele-epistemology [G01]Networked control and tele-epistemology [G01]

Sensor networksSensor networks Not necessarily wireless or energy constrainedNot necessarily wireless or energy constrained One component of sense-actuator networksOne component of sense-actuator networks

CharacteristicsCharacteristics Heterogeneous collection of networked sensors, Heterogeneous collection of networked sensors,

actuators, controllersactuators, controllers Power Power

Often plentiful, sometimes limitedOften plentiful, sometimes limited Communication Communication

Often wired, sometimes low-bandwidth wirelessOften wired, sometimes low-bandwidth wireless Critical requirements: Critical requirements:

SafetySafetyStabilityStabilityDependabilityDependabilityRobustnessRobustnessQoSQoSScalabilityScalabilityAdaptabilityAdaptability

Information FlowInformation Flow

FlowFlow Sensor dataSensor data Remote controllerRemote controller Control packetsControl packets

Timely deliveryTimely delivery StabilityStability SafetySafety PerformancePerformance

OutlineOutline

OutlineOutline Introduction to Sense-and-RespondIntroduction to Sense-and-Respond Bandwidth AllocationBandwidth Allocation Future of Cyber-Physical InfrastructureFuture of Cyber-Physical Infrastructure

WarningWarning Most EE-oriented talk I could possibly giveMost EE-oriented talk I could possibly give Avoid redundancy with previous talksAvoid redundancy with previous talks

Bandwidth AllocationBandwidth Allocation

Bandwidth AllocationBandwidth Allocation

DefinitionDefinition Multiple sense-and-respond Multiple sense-and-respond

flowsflows Contention for network Contention for network

bandwidthbandwidth

DesiderataDesiderata Stability and performance of Stability and performance of

control systemscontrol systemsMust account for physicsMust account for physics

Efficiency and fairnessEfficiency and fairness Fully distributed, Fully distributed,

asynchronous, and scalableasynchronous, and scalable Dynamic and self-Dynamic and self-

reconfigurablereconfigurable

Control and NetworksControl and Networks

Control Control overover Networks (C Networks (Cover over N)N) NCSs, DCSs, SANETs, CPs, …NCSs, DCSs, SANETs, CPs, …

Control Control ofof Networks (C Networks (Cof of N)N) Efficient BW allocationEfficient BW allocation

Regulate the packet injection rateRegulate the packet injection rate

““CCof of N” scheme to better serve “CN” scheme to better serve “Cover over N” N”

Control Control ofof Networks Networks

A bandwidth allocation schemeA bandwidth allocation scheme

Formulate the scheme as a Control Formulate the scheme as a Control problemproblem

Control systems regulate sending rate Control systems regulate sending rate based on congestion signal fed back from based on congestion signal fed back from the networkthe network

Sampling Rate and Sampling Rate and Network CongestionNetwork Congestion

h=1/r

l1 l2

Problem FormulationProblem Formulation

Define a utility fn Define a utility fn UU((rr) ) that isthat is Monotonically increasingMonotonically increasing Strictly concaveStrictly concave Defined for Defined for rr ≥ ≥ rrminmin

Optimization formulationOptimization formulation

( )

min,

max ( )

s.t. , 1,...,

and

i ii

i li l

i i

U r

r C l L

r r

S

Distributed ImplementationDistributed Implementation

Two independent algorithmsTwo independent algorithms End-systems (plants) algorithm End-systems (plants) algorithm Router algorithm (later on)Router algorithm (later on)

Plant ControllerRouter

max

min

1( ) 1 ' ( )r

rt tp pr h U

p p

p

NCS-AQM Control LoopNCS-AQM Control Loop

tf

q(t)f(q(t))q`=Σr(t) - C

p(t)

tb

1( ) ' ( )r p U p

Plant Queue

sdBes

QueueController

G(s)

Queue Controller Queue Controller G(s)G(s)

Proportional (P) Controller Proportional (P) Controller GGPP(s) = k(s) = kpp

Proportional-Integral (PI) ControllerProportional-Integral (PI) Controller GGPIPI(s) = k(s) = kpp ++ k kii//ss

q(s)G(s) P(s)

q0

+ _e u

Determination ofDetermination of k kpp andand k kii

Stability region in the Stability region in the kkii–k–kp p planeplane Stabilizes the NCS-AQM closed-loop system for Stabilizes the NCS-AQM closed-loop system for

delays less or equal delays less or equal dd

Analysis of quasi-polynomials, Analysis of quasi-polynomials, f(s,ef(s,ess))

Simulations & ResultsSimulations & Results

50 Plants:

( ) ( )dx

ax t bu tdt

/ ( ) a ra bKU r e

a

min ln

ar

bK abK a

()

((

))j

ju

tK

Rx

t

[Branicky et al. 2002]

[Zhang et al. 2001]

Simulations & Results (cont.)Simulations & Results (cont.)

PI¤

P¤

Related WorkRelated Work

Congestion Control Congestion Control Primarily addresses elastic flowsPrimarily addresses elastic flows Active Queue Management (AQM)Active Queue Management (AQM) Utility maximization and controllers often viewed as Utility maximization and controllers often viewed as

alternative approachesalternative approaches

Multi-media congestion controlMulti-media congestion control E.g., Equation-basedE.g., Equation-based Smooth rate variationSmooth rate variation No physically relevant utilityNo physically relevant utility

Time-scales Time-scales Approach to define time-varying utility functionsApproach to define time-varying utility functions ““C of N” missingC of N” missing

OutlineOutline

OutlineOutline Introduction to Sense-and-RespondIntroduction to Sense-and-Respond Bandwidth AllocationBandwidth Allocation Future of Cyber-Physical InfrastructureFuture of Cyber-Physical Infrastructure

WarningWarning Most EE-oriented talk I could possibly giveMost EE-oriented talk I could possibly give Avoid redundancy with previous talksAvoid redundancy with previous talks

Cyber-Physical SystemsCyber-Physical Systems

Foundations and Foundations and technologies for rapid and technologies for rapid and reliable development and reliable development and integration of computer-integration of computer-centric physical and centric physical and engineered systemsengineered systems

““Globally virtual, locally Globally virtual, locally physical”physical”

Major NSF initiative Major NSF initiative plannedplanned

Needs and DirectionsNeeds and DirectionsNeeds and DirectionsNeeds and Directions

New CalculusNew CalculusMerge time- and event-based systemsMerge time- and event-based systems

New ToolsNew ToolsE.g., co-simulation for co-designE.g., co-simulation for co-design

New Networks methodsNew Networks methodsBandwidth allocation, play-back buffersBandwidth allocation, play-back buffers

New EducationNew EducationMulti-disciplinary educationMulti-disciplinary education

Telltale sign: New MetricsTelltale sign: New Metrics Network-oriented metricsNetwork-oriented metrics

Delay, jitter, loss rates, bandwidthDelay, jitter, loss rates, bandwidthImpacts physics, but different from physics behaviorImpacts physics, but different from physics behavior

Control-Theoretical metricsControl-Theoretical metricsOvershoot, rise time, settling time, etc.Overshoot, rise time, settling time, etc.Hard to relate to network conditionsHard to relate to network conditions

Multi-disciplinary metricsMulti-disciplinary metricsE.g., plant tracking in terms of network bandwidth allocationE.g., plant tracking in terms of network bandwidth allocation

An E-Model for cyber-physical systems?An E-Model for cyber-physical systems?

ExampleExample

PI¤

P¤

AcknowledgmentsAcknowledgments

StudentsStudents Ahmad al-HammouriAhmad al-Hammouri David RosasDavid Rosas Zakaria Al-QudahZakaria Al-Qudah Huthaifa Al-OmariHuthaifa Al-Omari Nathan WedgeNathan Wedge Qingbo CaiQingbo Cai Prayas AroraPrayas Arora

ColleaguesColleagues Michael S. Branicky Michael S. Branicky Wyatt S. NewmanWyatt S. Newman

ConclusionsConclusions

Sense-and-RespondSense-and-Respond Merge cyber-world and physical worldMerge cyber-world and physical world Critically depends on physical timeCritically depends on physical time

Bandwidth AllocationBandwidth Allocation Control of Networks to aid Control over NetworksControl of Networks to aid Control over Networks Complete characterization of the stability regionComplete characterization of the stability region EvaluationEvaluation Peak detectionPeak detection

Cyber-physical systemsCyber-physical systems

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