Advanced Software Engineering course - Guest Lecture A4WSN- Architecture 4 Wireless Sensor Networks Here you can find the research paper presenting the concepts described in this lecture: http://goo.gl/XBB4k This presentation has been developed in the context of the Advanced Software Engineering course at the DISIM Department of the University of L’Aquila (Italy). http://www.di.univaq.it/malavolta

1. Università degli Studi dell’Aquila
Ivano Malavolta
DISIM Department, University of L’Aquila
ivano.malavolta@univaq.it

2. The material in these slides may be freely reproduced
and distributed, partially or totally, as far as an explicit
reference or acknowledge to the material author is
preserved.
Ivano Malavolta

3. Problem Definition
A4WSN
Software Architecture
Nodes Configuration
Physical Environment
Keeping Models Integrated
Exercise

4. 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.

5. 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.

6. From the SESENA 2012CfP:
Abstraction
“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”
Separation of
concerns
Model-based
Analysis

7. Abstraction
by masking the complexity of low-level, hardware details
Separation of
concerns
by clearly separating SW, HW, and deployment aspects of
a WSN
Model-based
Analysis
by facilitating the analysis of both functional and nonfunctional properties

8. in this lecture we focus on this part
Abstraction
Separation of
concerns
Model-Based
Analysis

10. Problem Definition
A4WSN
Software Architecture
Nodes Configuration
Physical Environment
Keeping Models Integrated
Exercise

11. It is composed of 3 modeling languages
Details about
WSN nodes
Software
Architecture
Physical
environment

12. Structure
components
ports
application data
messages
Behaviour
events
conditions
actions

13. 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.

14. 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

15. 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}
* not supported in the current version of the tool

16. Operations on Application Data:
• arithmetic
•
+ - / *
Assignment is done via
a dedicated Action in
the behaviour
• boolean
•
AND, OR, NOT
• relational
•
> >= < <= !=
threshold + 30
Application data reference
Structured elements reference
person.name
readings[1]
rooms[“key1”]

17. Each Component can contain a description of its behaviour
The behaviour is based on:
1. Events-conditions-actions
2. Modes

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

28. Problem Definition
A4WSN
Software Architecture
Nodes Configuration
Physical Environment
Keeping Models Integrated
Exercise

29. Types of nodes
OS
MAC protocol
routing protocol
installed sensors
installed actuators
energy sources
communication devices

30. 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, ...

31. Node
ADC
Microcontroller
DAC
Memory
CPU
CPU
CPUs
RF
Timer
Storage memory
Program memory
Energy Source
Energy Source
Energy Sources
Sensors
Sensors
Sensors
Memory
Additional
Memory
memories
RF
RF
RFs
Actuators
Actuators
Actuators

32. 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, ...

33. 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

34. • 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

35. Microcontroller (one)
represents the entity which performs tasks, processes data
and controls the functionality of other components in the
sensor node
Microcontroller
1_*
0_*
0_*
ADC
DAC
Memory
1_1
CPU
CPU
CPU
0_1
RF
Timer 1_*
Program memory
1_1

36. • 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

37. • 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

38. 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

39. Problem Definition
A4WSN
Software Architecture
Nodes Configuration
Physical Environment
Keeping Models Integrated
Example

40. A 2D space with obstacles
freely positioned
with their own shape
with attenuation coefficients

41. 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

42. 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

43. 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
A1
A2
A3

44. Problem Definition
A4WSN
Software Architecture
Nodes Configuration
Physical Environment
Keeping Models Integrated
Example

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

46. 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

47. 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

48. 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

49. 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

50. Nodes can be distributed in three different ways:
Random
Grid
Custom
each node is placed
nodes are placed on a
each node can be manually
randomly within the area
grid with a certain
number of rows and
placed within the area
columns
N2
N1
N1
N3
BS

51. In custom distribution, each node can be
individually specified in the area by:
1. its name
N2
N1
N1
BS
N3
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

52. Graphical and Tree-based editor for SAML & NODEML
tree-based
editor
models
graphical
editor
bird
view
properties
palette

53. ENVML: Graphical editor with background image
MAPML: Tree-based editor
DEPML: Tree-based editor

54. languages
refinement
code
generators
analysis
tools

55. 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.