COST 285 Modelling and Simulation Tools for Research in Emerging Multiservice Telecommunications

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COST 285Modelling and Simulation Tools for
Research in Emerging Multi-service
Telecommunications

• Francesco Potortì
• ISTI (Istituto di Scienza e Tecnologie
  dellInformazione)
• CNR (Consiglio Nazionale delle Ricerche)
• Pisa Italy

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Main scientific interests

• Communication protocols, especially at the MAC
  level and transport level
• Satellite multiple access protocols in TDMA mode
• Countermeasures against the atmospheric fading of
  satellite signals
• Mobile ad hoc networks with using 802.11 and
  Bluetooth protocols, especially at the MAC level
• Quality of service on the Internet
• TCP over satellite and terrestrial wireless
• Simulation in all of the above topics
• Characterisation of wireless channels (802.11,
  GPRS)

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Affiliation

• ISTI (Istituto di Scienza e Tecnologie
  dellInformazione) is part of the CNR (Consiglio
  Nazionale delle Ricerche)
• It was born in Pisa, in 2002, as the result of a
  merger between CNUCE-CNR and IEI-CNR
• I am a member of the Wireless Networking Group,
  composed of about 10 persons
• I am currently involved into two research
  projects
• TANGO, an Italian research project aimed at
  multilayer, multiservice Internet networks
• IS-MANET, an Italian research project aimed at
  mobile ad hoc networks in hostile environments
• I promote the use of free software in research
  environments

4
Simulation expertise

• Implementation of MTG, an Ethernet traffic
  generator used to measure the performance of
  FODA/IBEA
• Implementation and performance measurement of
  FODA/IBEA, a multiple-access satellite system
• Implementation of fracas, a discrete-time
  simulator for framed access channels, and its use
  to evaluate the performance of several satellite
  access systems
• Implementation of a fractal traffic generator
• Implementation of GaliLEO, a prototypal
  event-driven simulator for LEO satellite systems
• Analytical analysis of TCP over satellite
  channels

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Fracasthe Framed Channel Access
SimulatorFrancesco Potortì

• A very specialised simulator for communications
  protocols written in standard C
• Very small and very fast
• Able to study the behaviour and the performance
  of multiple-access protocols, usually at the MAC
  level
• Used until now for satellite channel access
  protocols
• Provides unsophisticated but comprehensive
  statistics
• Wrapper in Python for independent replications

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Scope of the simulation

• Multiple-access methods that use a time-framed
  communications channel
• In principle, usable for any such type of
  channel the framed channel of FDDI2, but not
  FDDI, unless the time is artificially subdivided
  in frames, putting a lower boundary on time
  resolution
• In practice, always used for geostationary
  satellite access
• The core is very small, consequently
• the access method can be as general as possible,
  with only the time frame constraint
• programming is not easy, and requires knowledge
  of all the inner structures of the simulator

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General architecture
Station 1
worker
worker
statistics collector
worker
worker
worker
frame allocations
Stat. 2
Station 3
Station 4
Station 1
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Traffic generators

• Each produces a number of Transmission Units per
  frame
• Each generator is attached to a single station
• Any number of generators can be attached to a
  station
• Built-in generators include
• two-state periodic fixed rate can be used for
  one-shot
• two-state periodic Poisson can be used for
  one-shot
• two-state Markov-modulated Poisson
• two-dimensional (NxM states) Markov-modulated
  models VBR traffic
• fractional Gaussian white noise models generic
  aggregate traffic
• specialised generators model batch interactive
  traffic

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The stations and the allocator

• All traffic is expressed as the number of
  Transmission Units
• TRUs are produced by generators, queued at the
  stations, and sent according to the allocations
  in the current frame
• TRUs are not received Fracas only simulates
  sending
• For each frame, each station
• Queues traffic produced by attached generators
• Drops traffic exceeding the queue length
• Sends queued TRUs filling the allocation in the
  current frame
• Asks the allocator for allocation in a future
  frame
• For each frame, the allocator sets up the
  allocation for the future frame as TRUs available
  to each station

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Emulator core loop

• do
• frame_number 1
• for_all_stations_do
• input run_generators (this_station)
• queue input
• sent min (queue, allocation)
• queue - sent
• request compute_request (this_station)
• compute_allocations (frame_number
  allocation_delay)
• gather_statistics (frame_number)
• while (! Stop_condition ())
• run_workers_and_print_results ()

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Allocator policies

• An allocator defines an allocation policy, which
  is an algorithm for computing the allocations for
  each station at a future frame based on their
  requests in the current frame
• Built-in policies are those that we really used
  in simulation work others may be added as
  necessary
• Currently implemented policies
• fixed TDMA a fixed assignment to each station
• FODA/IBEA developed at CNUCE, experimented with
  a prototype
• VnL-DA VBR allocation developed at CNUCE
• FEEDERS distributed allocation scheme developed
  at CNUCE
• DRIFS distributed allocation scheme developed
  at CNUCE
• CFRA developed at ENST - Toulouse (FR)

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Output statistics

• At each frame, several observables are collected
• Each worker computes a different statistics on
  one or more observables, including
• TRUs input, queued, dropped, allocated,
  requested, sent by stations
• allocation unused by stations
• transmission delay, either per frame or per TRU
• Some workers produce their results at emulation
  time
• Others produce a result at the end of the
  emulation
• A Python wrapper around Fracas is used to obtain
  estimates of a statistics inside a given
  confidence interval using independent
  replications of the same emulator run

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Classes of traffic

• Fracas distinguishes among four different classes
  of traffic, hierarchically ordered as follows
  stream, vbr, interactive, bulk, whose names
  reflect their supposed usage
• When emptying the station queues, the simulation
  core starts from stream, and gives any unused
  allocation to lower-grade traffic classes
• Usage of the classes is optional possibilities
  include
• gathering statistics for traffic generated in
  different classes
• defining different allocation policies for each
  class
• Use of classes enables the definition of complex
  allocation strategies

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Fracas summaryFrancesco Potortì

• A lightweight, portable simulator specialised for
  the study of multiple-access allocation schemes
• Traffic generators, allocation policies and
  statistics computations can each be added as
  separate modules
• Many built-in modules are implemented and have
  been used in research work
• Fracas has been validated by checking against a
  prototypal implementation of the FODA/IBEA
  allocation algorithm
• A paper on the architecture of Fracas has been
  published on Telecommunications Systems in 1999

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GaliLEO progress reportLaurent Franck and
Francesco Potortì

• A comprehensive simulator for satellite
  constellations, targeted towards LEO/MEO
  communication systems
• Experience from previous projects (SimToc,
  LeoSim, Fracas), involves different academic
  institutions
• Free software entirely implemented in Java
• Possible studies include
• algorithms for cell frequency reuse
• QoS routing for both UDL and ISL
• QoS aware channel access techniques

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Capacity of global coverage

• Emulation of an entire constellation
• Definition of individual earth stations and
  traffic generators
• Complete map of traffic patterns
• Ability to individually follow any traffic
  connection

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Study of a limited region

• Emulation over a limited geographical region
• Detailed and realistic traffic generation
• complex access techniques
• complex frequency reuse strategies
• Nearby network simulated by mathematical
  description

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Basic terminology

• A UDL (up-down link) covers a satellites
  footprint
• A UDL is made of beams, each covering partially
  overlapping cells
• Satellites are connected by ISLs
• A station is fed by one or more traffic
  generators

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Architecture of GaliLEO

• An event scheduler is at the core of the
  simulation engine
• The core modules come with the simulator
• Custom modules can be added at will
• Custom modules include traffic generators,
  constellation layouts, access protocols etc.

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The two inner layers

• The simulation engine provides
• the event scheduler
• the framework for building modules
• the communications facility between modules
• the input file structure, statistics gathering
  and display facility
• The standard modules provide some basic features
• a Leonet and a polar constellation
• a deterministic periodical traffic generator
• scalar resources for allocation in stations and
  satellites
• simple routing and load-dependent adaptive
  routing
• basic allocation strategies for stations and
  satellites
• basic station and satellite structures

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The simulation engine
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Demo setup

• 12 stations evenly distributed between 45N and
  45S
• Leonet constellation (15 satellites on 3 orbits)
• ISL capacity is 20 connections, UDLs is 80
  connections
• Measuring the connection blocking probability
• For each connection, the first and last
  satellites are those with max elevation
• The demo is made of three steps, global traffic
  is the same for all steps
• 6 Erlangs per station, static routing
• 4 adjacent stations at 10 Erlangs, others at 4
  Erlangs, static routing
• same traffic as previous case, adaptive routing

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Demo results
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GaliLEO summaryLaurent Franck and Francesco
Potortì

• A big simulator for LEO/MEO communication systems
• Both overall earth view and geographically
  limited studies are considered
• Very modular standard modules available, custom
  modules written in Java can be added
• Programming environment is Java
• Work in progress development is open to
  contributions
• Some features usable today for research demo
  available
• Home page at http//galileo.tesa.prd.fr/