A comparison of the architecture of network simulators NS2 and TOSSIM Seminar Performance Simulation

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A comparison of the architecture of network
simulators NS-2 and TOSSIMSeminar
Performance Simulation of Algorithms and
ProtocolsStudienprojekt CUBUSMichael Karl
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Overview

• Introduction and Motivation
• Architecture of TOSSIM
• What is TOSSIM?
• Architectural overview
• Component Graphs
• Events
• Models
• Communication Services
• Visualization Tool
• Conclusion

• Architecture of NS-2
• What is NS-2 ?
• Architectural Overview
• Network Components
• Event Scheduler
• Languages
• - Otcl / Tclcl / Tcl 8.0
• Visualization Tool

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Introduction and motivation

• Introduction
• Network simulation has a long history
• Most network simulators have some drawbacks
• Network simulators have widely varying focuses
• Motivation (in general)
• Study of the architecture of network simulators
  offers insight into their design, functions and
  working method.
• Motivation (for the Studienprojekt CUBUS)
• We need to know how other network simulators are
  designed and how they are working to develop and
  understanding of how to design CUBUS
• Understanding of their structure is essential for
  beeing competitive with them and achieving better
  performance results

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What is TOSSIM?

• TOSSIM
• A discrete event simulator for TinyOS wireless
  sensor networks
• TOSSIM and TinyOS were developed at UC Berkeley
• Can simulate thousands of nodes simultaneously
• Every mote in a simulation runs the same TinyOS
  program
• Provides configurable debugging output
• TinyOS
• stands for Tiny Microthreading Operating System
• Sensor network operating system
• runs on sensor nodes, so-called motes

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Architectural overview on TOSSIM

• TOSSIM architecture is composed of 5 parts
• TinyOS Component Graphs
• Execution Model (Events)
• Hardware abstraction components
• Models (Radio and ADC Models)
• Communication Services

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TinyOS Component Graphs
command
event

• A TinyOS program is a graph of components
  (component graph).
• Each TinyOS component has
• - a frame
• - a structure of private variables
• - three computational abstractions
• - Commands, events and tasks
• Commands and events
• - are mechanisms for inter-component
  communication
• Tasks
• - are used to express intra-component
  concurrency.

• A command is typically a request to a component
  to perform some service.
• An event signals the completion of that service.

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Execution Model (Events)

• Events
• A simulator event queue sits at the core of
  TOSSIM.
• This event queue delivers the interrupts that
  drive the execution of a
  TinyOS application.
• TOSSIM models each TinyOS interrupt as a
  simulation event.
• Simulator events run atomically with respect to
  one another.
• After each simulator event executes, TOSSIM
  checks the task queue for any pending tasks, and
  executes all of them in FIFO (First-In,
  First-Out) scheduling order.
• When a simulator event calls an interrupt handler
  (in the TOSSIM hardware abstraction components)
  the interrupt handler signals TinyOS events and
  calls TinyOS commands.
• These TinyOS events and commands again post tasks
  and cause further simulator events to be
  enqueued, driving execution forward.

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Models (Radio and ADC Models)

• The TOSSIM architecture include two different
  models
• Radio models for all kinds of transmission
  aspects and
• ADC models for the Analog-Digital-Converter.
• Radio Models
• TOSSIM uses a very simple abstraction for a
  network signal, it is either a one or a
  zero.
• All transmission signals have equal strength.
• Collision is modeled as a logic OR.
• Disadvantage Distance does not effect signal
  strength.
• TOSSIM provides two built-in radio models
• the simple radio model
• the lossy radio model

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Radio Models

• simple
• places all of the nodes in a single radio cell
• every bit transmitted is received error-free
• no bits are corrupted due to error
• Disadvantage two motes transmitting at the same
  time can
• lead to problems
• lossy
• places the nodes in a directed graph with bit
  error probabilities
• Each edge (u, v) in the graph means that the
  signal of node u can be heard by node v.
• Every edge has a weight that indicates the
  probability that a bit sent by node u will be
  corrupted (and therefore flipped) when node v
  hears it.

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ADC Models (1)

• ADC Models
• ADC stands for Analog-Digital-Conversion.
• An Analog-Digital-Conversion is an electronic
  process in which a continuously variable (analog)
  signal is changed, without altering its essential
  content, into a multi-level (digital) signal.
• TOSSIM provides two ADC models
• random and
• generic

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ADC Models (2)

• random
• The ADC has several channels that can be sampled.
• If any of the channels are sampled, it returns a
  10-bit random value.
• generic
• has the functionality of the random model but in
  addition to that
• provides also the possibility to be actuated by
  external applications
• By using the TOSSIM control channel, external
  applications can set the value for any ADC port
  on any mote.
• TinyViz does this through the ADC plugin.

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Hardware abstraction components

• Hardware abstraction components
• The TinyOS operating system running on motes
  abstracts each hardware resource as a component.
• TOSSIM takes advantage of that by replacing only
  a small number of these components (such as the
  ADC, the Clock, the EEPROM, etc.).
• TOSSIM emulates the behavior of the underlying
  raw hardware.
• TOSSIM models these components in the hardware
  abstraction components part of the architecture.

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Communication Services

• Tossim
• provides mechanisms that allow PC-application to
  communicate with TOSSIM
• this happens via TCP/IP
• has a command/event interface that mediates
  between PC applications and the simulation.
• TOSSIM signals events to applications, providing
  data on a running simulation
• Applications call commands on TOSSIM to actuate a
  simulation or modify its internal state.

response
signals events
signals events
Command/event interface
TOSSIM
PC application
calls commands
calls commands
request
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Visualization Tool
Interactive plugins

• Tiny Viz
• is a visualization and actuation environment for
  TOSSIM
• Java-based graphical user interface application
• can be attached to a running simulation
• Uses a plug-in architecture to allow for
  expansion
• Provides debugging and visualization output
• Interacts with Tossim simulations of TinyOS
  applications

• Plugins
• ADC Readings
• Debug messages
• Sent radio packets

Simulation visualization
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What is NS-2?

• ns2 stands for network simulator (ver 2)
• Discrete event simulator targeted at networking
  research.
• Focuses on the simulation of IP networks on the
  packet level.
• Wired and wireless
• Object-oriented Tcl (Otcl) script interpreter
  with network simulation object libraries.

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Architectural overview on NS-2

• NS architecture is composed of 5 parts
• Discrete event scheduler
• Data network (the Internet) components
• Tclcl C and otcl linkage
• OTcl Object-oriented support
• Tcl8.0 scripting language

Event Scheduler
ns-2
Tclcl
Network Component
OTcl library
Tcl8.0
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Discrete Event Scheduler

• Event scheduler
• to drive the execution of the simulation,
• to process and schedule simulation events
• For network components that simulate
  packet-handling delay or that need timers.

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Network Components

• Class hierarchy
• NS models all network elements through a class
  hierarchy.
• TclObject class is the superclass of all OTcl
  library objects (network components, event
  scheduler, timers and others).
• NsObject again is the superclass of all basic
  network component objects that handle packets.
• Connector is the superclass of all basic
  network objects that have only one output data
  path and
• Classifier is the superclass of all switching
  objects that have possible multiple output data
  paths.

• Network objects, such as nodes and linkes can
  then be composed of this basic network
  components.

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C and OTcl Separation

• data / control separation NS separates the
  control and data path because of efficiency
  reasons.
• C for data
• per packet procssing, core of ns
• fast to run, detailed, complete control
• OTcl for control
• Simulation scenario configurations
• Periodic or triggered action
• Manipulating existing C objects
• fast to write and change
• Advantage running vs. writing speed
• Disadvantage Learning and debugging (two
  languages)

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OTcl and C The Duality
the compiled objects are made available
to the OTcl interpreter

• Otcl and C
• OTcl and C share class hierarchy.
• The compiled C objects are made available to
  the OTcl interpreter through an OTcl Linkage.
• The OTcl linkage creates a matching OTcl object
  for each of the C objects.
• In this way, the controls of the C objects are
  given to OTcl.

the event scheduler and the basic network
component objects in the data path
C objects data path handling OTcl Objects
control path handling
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Visualization Tool

• Nam
• stands for network animator
• The NS visualization tool
• visualizes ns (or other) output
• only visualization, no actuation or generation of
  simulation prgram
• only animation of simulation output
• -gt Nam editor GUI interface to generate ns
  scripts

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Conclusion

• What is different?
• The network simulators NS-2 and TOSSIM focus on
  different aspects and have therfore totally
  different architectures
• - NS-2 focuses on the simulation of network
  nodes at the packet level.
• - TOSSIMs approach is to simulate the TinyOS
  sensor networks at bit
• level granularity.
• What do they have in common?
• Both simulators have some kind of event handling
  mechanism to cope with the processing of events.
• - TOSSIM Discrete event queue
• - NS-2 Event scheduler

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Thanks for your attention
Questions?