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

1. COST 285Modelling and Simulation Tools for Research in Emerging Multi-service Telecommunications Francesco Potortì ISTI (Istituto di Scienza e Tecnologie dell’Informazione) CNR (Consiglio Nazionale delle Ricerche) Pisa – Italy

2. 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)

3. Affiliation • ISTI (Istituto di Scienza e Tecnologie dell’Informazione) 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

5. 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

6. 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

7. worker generator requester allocator generator generator Station 2 generator generator allocation delay generator Station 3 generator Station 4 General architecture Station 1 worker worker statistics collector worker worker worker frame allocations Stat. 2 Station 3 Station 4 Station 1

8. 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

9. 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

10. 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 ();

11. 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)

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. Basic terminology • A UDL (up-down link) covers a satellite’s 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

19. 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.

20. 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

21. The simulation engine

22. Demo setup • 12 stations evenly distributed between 45°N and 45°S • Leonet constellation (15 satellites on 3 orbits) • ISL capacity is 20 connections, UDL’s 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

23. Demo results

24. 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/