TopDown Protocol Design with UML

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Top-Down Protocol Design with UML

• Jason Shamberger
• October 13, 2000

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Outline

• PicoRadio Application
• Brief Introduction to UML
• Design Methodology
• UML Description of PicoRadio
• Conclusion/Future Work

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SmartBuilding A PicoRadio Application

• Environmental control for an office building
• Three types of nodes
• Sensors measure some physical property either
  reactively or proactively
• Actuators affect some change on the environment
• Monitors controlling nodes, issue requests to
  sensors and commands to actuators
• Data measured includes temperature, light,
  humidity, sound, air quality, smoke, security
  sensors, etc.

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SmartBuilding A PicoRadio Application

• Example subsystem controlling temperature for
  one workspace
• Several temperature sensors
• One actuator (AC vent)
• One control monitor running an algorithm to
  maintain a constant temperature
• One UI monitor (touchpad) allowing user to change
  the parameters in the control function to raise
  or lower the temperature
• One system monitor which logs statistics, changes
  control functions systemwide to minimize power
  consumption, configures and debugs the system

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What is UML (Unified Modeling Language)?

• UML is a language designed to model
  object-oriented software systems.
• Consists of several different types of diagrams
• Use Case diagrams show environment interactions
  with system
• Class diagrams show relationships between sets of
  objects that share common attributes and
  operations, give static structure of system
• Interaction diagrams (Message Sequence Charts)
  show how objects interact dynamically
• And more

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Our Use of UML

• Provide specifications for system we are
  designing
• More formal description than English
• Document the design process
• NOT Simulating the system
• Use another tool for this (OpNet)
• NOT Implementing the system
• Use another tool for this (VCC)

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UML Notation

• Most of our designs are class diagrams
• Show relationships between classes
• General relationship
• Inheritance (is a) relationship
• Aggregation (has a) relationship
• Dependency (uses) relationship

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Communication-Based Design Methodology

• In a methodology for communication-based design
  developed by researchers in the Metropolis group
• Processes communicate across channels
• Initially assume the channel is ideal, so the
  input-output relation is the identity. If the
  behaviors of the processes are incompatible this
  can be fixed by adding behavior adapters
• Where the channel is not ideal (or when we refine
  the channel to include its imperfections), we
  must add a channel adapter so that within an
  acceptable tolerance, the channel behaves as
  ideal

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Layers

• As we design a protocol, these channel adapters
  we add form layers of abstraction
• Our design methodology starts at the top and
  descends through these layers
• We simultaneously refine the communication medium
  to move closer to the real world conditions, and
  add channel adapters to cope with these conditions

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Function to Architecture Mapping

• At each layer we are performing a mapping
• Map a functionality we wish to implement onto a
  refined hardware
• The result is a new functionality, which has
  gained properties of the hardware, and possibly
  adapters

Level 0 Functionality
Level 0 Architecture
mapping
Level 1 Functionality
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Specifications

• System is a control system for building
  environment
• Keeps properties of the environment (temperature,
  light, etc.) within certain tolerances
• Data sizes and rates specified during meeting
  with CBE people
• Use case captures interactions with environment

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Use Cases
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Level 0 Functionality

• System has three global functions
• Sensor maps physical property of environment
  into a number Ns.
• Controller maps Ns to NA using some control
  algorithm.
• Actuator maps NA to some physical property of
  environment.

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Level 0 Functionality
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Level 0 Architecture

• Architecture consists of
• A number of nodes, each has a location (can
  include some uncertainty) and other physical
  properties
• An unspecified communication medium

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Level 0 Architecture
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Level 1 Functionality

• Partition (distribute) the global functions in
  time and space
• This is guided by the specifications, which state
  frequency with which sampling in time/space must
  occur.
• Select number of sensor, actuator, monitor nodes,
  locate them to minimize power, either through
  simulation or analysis

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Level 1 Functionality
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Level 1 Functionality (cont)
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Level 1 Architecture

• Introduce a fully-connected communication medium
• Given a message and an address, medium can
  deliver to any other node

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Level 1 Architecture
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Level 2 Functionality

• Level 1 nodes had separate ports to send to
  different destinations
• Add addressing adapters to map the end-to-end
  connections onto the fully connected network

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Level 2 Functionality
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Level 2 Functionality (cont)
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Level 2 Architecture

• Refine the communication medium to add
  attenuation properties
• Refine the nodes to add transmission power
• As a result, each node can only send messages to
  its neighboring nodes

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Level 2 Architecture
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Level 3 Functionality

• As a result of the limited transmission range,
  have to add routing adapters and repeater nodes
  to make the network multi-hop
• Design decisions at this level include choice of
  routing algorithm, whether to establish
  persistent connections

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Level 3 Functionality
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Level 3 Architecture

• Decompose the communication medium into a set of
  channels

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Level 3 Architecture
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Level 4 Functionality

• Each node can now transmit on one of many
  channels
• Add MAC adapters to allocate channels and deal
  with collisions

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Level 4 Functionality
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Conclusions/Future Work

• UML model has captured the big picture of the
  design.
• Needs more refinement, especially at network/MAC
  layer
• UML helps document the interfaces which will be
  used between each layer

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Conclusions/Future Work

• Interaction Diagrams can capture some
  inter-object behavior

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Current/Future Work

• Once we have described the system in UML,
  implement it in VCC

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Future Work

• UML functions well as a denotational language
• Helps describe our design in a more formal way
  than English text, and is easy to read and
  comprehend
• Can we add some semantics to UML so that it could
  be used as an input language to a system-design
  tool such as VCC?