Università degli Studi dell’Aquila

Ivano Malavolta

DISIM Department, University of L’Aquila ivano.malavolta@univaq.it

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Ivano Malavolta

Problem Definition

A4WSN

Software Architecture

Nodes Configuration

Physical Environment

Keeping Models Integrated

Exercise

WSNs consist of spatially distributed sensors that cooperate to accomplish some tasks.

Sensors are:

• small

• battery-powered

• with limited processing capabilities

• with limited memory

They can be easily deployed to monitor different environmental parameters such as temperature, movement, sound and pollution.

Sensors can be distributed on roads, vehicles, hospitals, buildings, people and enable different applications such as medical services, battlefield operations, crisis response, disaster relief and environmental monitoring.

From the SESENA 2012CfP:

“the development of WSN software is still carried out in a rather primitive fashion, by building software directly atop the OS and by relying on an individuals hard-earned programming skills”

“WSN developers must face not only the functional application requirements but also a number of challenging, non-functional requirements and constraints resulting from scarce resources”

Abstraction

Separation of concerns

Model-based Analysis

by masking the complexity of low-level, hardware details

by clearly separating SW, HW, and deployment aspects of a WSN

by facilitating the analysis of both functional and non-functional properties

Abstraction

Separation of concerns

Model-based Analysis

Abstraction Separation of

concerns Model-Based

Analysis

in this lecture we focus on this part

Problem Definition

A4WSN

Software Architecture

Nodes Configuration

Physical Environment

Keeping Models Integrated

Exercise

It is composed of 3 modeling languages

Software Architecture

Details about WSN nodes

Physical environment

Structure

components

ports

application data

messages

Behaviour

events

conditions

actions

Component. A unit of computation with internal state and well defined interface. Each component can contain a behaviour specification and a set of application data.

MessagePort. Specifies the interaction point between a component and its external environment.

Incoming messages arrive at InMessagePorts

Outgoing messages are sent via OutMessagePorts

Connection. It is a unidirectional communication channel between two message ports.

Application Data. Local variables declared in the scope of the component. It is manipulated by actions defined in the behaviour of the component.

There are two types of application data:

• Primitive

• integer, string, real, boolean

• Structured

• Enumeration

• Structure

• Array*

• Map*

* not supported in the current version of the tool

* not supported in the current version of the tool

threshold : integer = 30

temperature : real = 15,5

message : string = "hello“

found : boolean = false

status : enum{ON, OFF} = status.OFF

gender : enum{MALE, FEMALE}

person : struct{name: string, sex: gender} =

person("John", gender.MALE)

readings : array{integer} = [12, 34, 56]

rooms : map = {"key1": 5, "key2": status.OFF}

Operations on Application Data:

• arithmetic

• + - / *

• boolean

• AND, OR, NOT

• relational

• > >= < <= !=

Application data reference

Structured elements reference

Assignment is done via a dedicated Action in

the behaviour

threshold + 30

person.name

readings[1]

rooms[“key1”]

Each Component can contain a description of its behaviour

The behaviour is based on:

1. Events-conditions-actions

2. Modes

Each Component can perform actions:

Sense gets some data from a sensor and stores the read value into a specific application data

ex: get current temperature

Actuate activates and actuator, optionally an application data can be used to pass a parameter to the actuator

ex: actuate a water sprinkler

SendMessage sends a message via a specific message port

Optionally, the payload of the message can be specified by passing an expression as parameter

Types of available messages:

Unicast to a single receiver

Multicast to a set of receivers

Broadcast to every node containing the target component

StartTimer starts a timer which can be triggered later

cyclic: true if the timer must be periodic

delay: the time (in millisecs) that must pass before the first activation

period: the period of the timer (in millisecs), if it is a cyclic one

StopTimer stops a previously started timer

StoreData puts some expression into an application

data of the component

CallSyncService calls an external service (ex. web service)

data: optional, it is the parameters that can be passed to the service

dataRecipient: the application data which will be filled with the result

CallAsyncService calls an external service, the result of the call will be available via a dedicated event

data: optional, it is the parameters that can be passed to the service

Fork splits the incoming behavioural flow into a set of parallel flows

Join merges incoming behavioural flows and syncs them into a single outgoing flow

Choice, depending on the value of the conditions in its outgoing links, one and only one control flow is executed

ReceiveMessage is triggered when the component receives a message

dataRecipient: the application data which will contain the payload

fromMessagePort: the port that received the message

TimerFired is triggered when a previously started timer is activated

Each component can react to specific kinds of events:

ServiceCallback is triggered when the result of an AsyncServiceCall is available

dataRecipient: the application data which will be filled with the result

ServiceCall is triggered when some king of external service interacts with the component

dataRecipient: the application data which will contain the parameters of the call

Behavioural flow is specified by means of Links

A link can exist:

1. from an event E to an action A: in this case after the event E is triggered, A will be executed

2. from an action A1 to another action A2: in this case, A2 is executed immediately after A1

Conditions are boolean expressions (optionally) associated to links

The execution flow goes through a link only if its condition evaluates to true

A mode is a specific status of the component

ex. sleeping mode, energy saving mode, etc.

Initial Mode is the first mode which is active when the component starts up

At any given time, one and only one mode can be active in a component

The component reacts only to those events which are defined within its currently active mode

A component can switch from a mode to another by means of mode transitions

Mode transitions link together modes by passing...

from a special kind of action called ExitMode

to a special kind of event called EnterMode

in this way actions and events can be linked to modes entry and exit points, creating a continuous flow among modes

Problem Definition

A4WSN

Software Architecture

Nodes Configuration

Physical Environment

Keeping Models Integrated

Exercise

Types of nodes

OS

MAC protocol

routing protocol

installed sensors

installed actuators

energy sources

communication devices

A nodes specification is composed of a set of WSN node types

Node Attributes:

• OS

• ex. TinyOS, Contiki, Mantis, LiteOS, ...

• macProtocol

• ex. T-MAC, S-MAC, WiseMAC, SIFT, ...

• routingProtocol

• ex. GEAR, LEACH, HEED, ...

Node

Energy Source Energy Source Energy Sources

Sensors Sensors Sensors

Actuators Actuators Actuators

Microcontroller Memory Memory Additional

memories

RF RF RFs

CPU ADC

DAC Timer

RF

CPU CPUs

Memory Program memory

Storage memory

The following elements can be attached to a WSN node:

• energy sources (one or more)

• continuous

• degradable (initialStoredEnergy in Joule)

• harvested (initialStoredEnergy in Joule, harvestingEnergyRate in Joule)

• sensors (zero or more)

energyConsumptionPerSample (mJ), idleEnergyConsumption (mJ)

ex. light sensor, temperature sensor, radio sensor, ...

• actuators (zero or more)

energyConsumptionPerSample (mJ), idleEnergyConsumption (mJ)

ex. water sprinkler, leds, lights, heating system switch, ...

A node can contain the following elements:

• RF Communication Device (zero or more)

represents the radio device to communicate with other nodes

Attributes:

float transmissionPower in dBm

float receiveSensitivity in dBm

float[1] frequency in MHz

float antennaGain in dBd

String modulation // name of the modulation method

String encryption // name of the enc. algorithm

• Memories (one or more)

represents external storage memories of the node

Attributes:

float averageReadingEnergyConsumption in mW

float averageWritingEnergyConsumption in mW

int[1] size in Kb

Microcontroller (one)

represents the entity which performs tasks, processes data and controls the functionality of other components in the sensor node

Microcontroller

CPU ADC

DAC Timer

RF

CPU CPU

Memory Program memory

1_* 0_*

0_*

0_1

1_*

1_1 1_1

• ADC (zero or more)

Attributes:

int resolution // # discrete values it can produce

int bits // 8 bits, 16 bits

int channels // #channels

• DAC (zero or more)

Attributes:

int resolution // # discrete values it can produce

int bits // 8 bits, 16 bits

• Processor (one or more)

Attributes:

int[1] frequency in MHz

float[1] cpi // cycles per instruction

• Timer (one or more)

Attributes:

int bits // 8 bits, 16 bits

• RF Communication Device (0_1) – internal radio transceiver

• Memory (one) – same role as RAM memory in PCs

• Program Memory (one) – stores the program running on the node

A Node can specify a set of Power Modes

Each power mode identifies a set of node elements (such as memory, DAC, RF comm. device, etc.) and distinguishes between which elements are active and which elements are disabled

Mode A Mode B

Problem Definition

A4WSN

Software Architecture

Nodes Configuration

Physical Environment

Keeping Models Integrated

Example

A 2D space with obstacles

freely positioned

with their own shape

with attenuation coefficients

The Environment represents the overall area in the 2D space in which the WSN will be deployed

Attributes:

string name // the name of the area

float [1] width // the width of the bounding box of the area

float [1] height // the height of the bounding box of the area

imagePath // the image used as background in the editor

The environment contains a set of Obstacles and Areas

An Obstacle specifies any kind of relevant element which can be placed in the environment

Attributes:

string material // the name of the material of the obstacle

(ex. concrete wall, wooden door, glass, ...)

float [1] attenuation // the “thickness” of the obstacle

// it ranges from 0 to 1

Coordinate [2_*] shell // the perimeter of the obstacle in the 2D space

An area is a portion of physical environment in which a type of node can be deployed

An area has a single property:

Shape: the perimeter of the area defined as a set of coordinates

A3

A1 A2

Problem Definition

A4WSN

Software Architecture

Nodes Configuration

Physical Environment

Keeping Models Integrated

Example

Two special models link together software components, nodes and environment specifications

MAPML models semantically represent the classical notion of deployment of software components onto HW nodes

Separation of Concerns

It helps in clearly separating the application layer of a WSN from all the other lower levels

this aspect is new in the WSN domain

Architects can focus on the application from a functional point of view in SAML, and only later they will focus on low-level aspects

Weaves together an SAML model and a NODEML model

It defines how components are deployed into each configured nodes

Types of link:

• Mapping maps a component to its corresponding node configuration

• Sensor Mapping maps a Sense action in a component to a Sensor in a node

• Actuator Mapping similar to the Sensor Mapping, but for actuators

• Communication Device Mapping maps a Message Port in a component to an RFCommunicationDevice in a node

• Mode Mapping maps a Mode in a component to a Power Mode in a node

Weaves together a NODEML model and an ENVML model

It defines how node configurations are

1. instantiated, and

2. virtually deployed in the physical environment

A DEPML model presents a single type of link: Deployment Link

A deployment link considers a node configuration in the NODEML model, and assigns it to an area within the physical environment

Each node type can be instantiated ”n” times within a specific area

this allow architects to focus on generic components and node types in SAML and NODEML, while in DEPML we consider the final shape of the network

Nodes can be distributed in three different ways:

Random

each node is placed

randomly within the area

Grid

nodes are placed on a

grid with a certain

number of rows and

columns

Custom

each node can be manually

placed within the area

BS

N1 N2

N3

N1

1. its name

2. the coordinates of its position

A nodes name pattern can be given to an area independently from the distribution type

they are used to have a way to refer to the names used as targets of Send

Message actions in SAML models

Available patterns:

name<number>, name<Letter>, name

BS

N1 N2

N3

N1

In custom distribution, each node can be individually specified in the area by:

Graphical and Tree-based editor for SAML & NODEML

bird view

graphical editor

properties

palette

models

tree-based editor

ENVML: Graphical editor with background image

MAPML: Tree-based editor

DEPML: Tree-based editor

languages refinement

code generators

analysis tools

Model a WSN that allows the personnel of an hospital to monitor patients’ vital sign data with the help of pulse-oximeters.

The monitoring system consists of two types of nodes:

• a monitoring station

• ten oximeter nodes

Those nodes form a star-network.

Each pulse-oximeter monitors the patient continuously and a measurement is sent to the monitoring station every 3 seconds.

In case the oximeter reads a value other than a defined threshold, an alert message is sent to the monitoring system, and the system goes into a warning mode in which sensor readings are sent to the monitoring station more frequently (i.e., once every 200 milliseconds), hence facilitating continuous monitoring of patients and allowing real-time responses in case of emergency conditions.