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Simulating Dynamic Bandwidth Allocation on Satellite Links

Simulating Dynamic Bandwidth Allocation on Satellite Links. Alberto Gotta, Francesco Potortì, Raffaello Secchi. Italian National Research Council (CNR) Istituto di Scienza e Tecnologie dell’Informazione “A. Faedo” (ISTI). DVB-RCS overview Architecture of Tdma-dama Extension to NS2

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Simulating Dynamic Bandwidth Allocation on Satellite Links

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  1. Simulating Dynamic Bandwidth Allocation on Satellite Links Alberto Gotta, Francesco Potortì, Raffaello Secchi Italian National Research Council (CNR) Istituto di Scienza e Tecnologie dell’Informazione “A. Faedo” (ISTI) Raffaello Secchi – WNS2

  2. DVB-RCS overview Architecture of Tdma-dama Extension to NS2 Demand Allocation Multiple Access Rate Based allocation policy Validation & Measurements Conclusions Summary Raffaello Secchi – WNS2

  3. DVB-RCS (ETSI EN 301 790) Bidirectional channels over satellite links (Meshed Networks) It defines an MF-TDMA medium access control It guarantees IP/DVB connectivity via satellite links DVB-RCS system RETURN LINK DVB-RCS FORWARD LINK DVB-S Raffaello Secchi – WNS2

  4. DVB-RCS network elements Forward Link Return Link RNCC TT RNCC NCC Gateway Raffaello Secchi – WNS2

  5. Deployment of DVB-RCS features into ns-2 Integration of TDMA access scheme into the ns-2 satellite environment Development of bandwidth allocation methods (CRA, RBDC, VBDC, FCA) Study of the interaction between transport and satellite MAC layer Congestion control (TCP, TCP friendly) over satellite links with dynamic bandwidth allocation Impact of MAC delay over delay-critical applications (e.g VoIP, video-conferencing, etc.) Tdma-dama objectives Raffaello Secchi – WNS2

  6. The current satellite module of ns-2 supports both geostationary satellite and polar orbiting LEO constellations with multiple users per downlink/uplink and asymmetric links Tdma-dama is a module in the MAC layer block which supports dynamic bandwidth allocation mechanisms IP packets fragmentation and encapsulation into a TDMA frame Fully customizable from Otcl Interface Tdma-dama in ns-2 Raffaello Secchi – WNS2

  7. DAMA allocation principle • Each traffic terminal periodically submits to a master terminal an allocation request based on the incoming traffic rate or traffic backlog at the terminal Traffic Terminals (Requesters) Master (Allocator) request Raffaello Secchi – WNS2

  8. The master station collects the request of all the active traffic terminals, computes a burst time plan and broadcasts it back to the terminals DAMA allocation principle Traffic Terminals (Requesters) allocation Master (Allocator) Raffaello Secchi – WNS2

  9. The time interval between the TTs requesting a given bandwidth and the system assigning it is called allocation delay Due to the large allocation delay on the satellite link, we can observe that the transmission delay dramatically increases when the rate of traffic incoming to a TT varies rapidly if the input rate increases in a time shorter than the allocation delay, the excess traffic is buffered at the traffic terminal, thus increasing the queuing delay Our simulative analysis confirms experimental findings Drawbacks of Dynamic Allocation Raffaello Secchi – WNS2

  10. The following methods can be combined in many ways: Constant Rate Assignment (CRA) Bandwidth is negotiated between the traffic terminal and the allocator at the beginning of each connection Rate Based Dynamic Capacity (RBDC) Each Traffic terminals submits to the allocator a bandwidth request message based on the rate of local incoming traffic Volume Based Dynamic Capacity (VBDC) Each terminal dynamically signals the data volume needed to empty its buffer Free Capacity Assignment (FCA) No explicit request comes from the terminals. Unused bandwidth is assigned automatically by the allocator to the traffic terminals according to some fairness criteria Bandwidth Allocation Methods Raffaello Secchi – WNS2

  11. Tdma-dama consists of two customizable C++ classes of agents The Requester agent, one for each satellite terminal, is responsible for calculating the bandwidth needed by the terminal and for submitting a request to the allocator. The Allocator agent computes the burst time plan, that is, the TDMA frame allocation for all stations. Tdma-dama Design Raffaello Secchi – WNS2

  12. Diagram of Tdma-dama Traffic terminal Satellite network MAC buffer Allocator agent Requester agent Terrestrial network TDMA fragmentation and reassembly satellite link PHY Tx/Rx Raffaello Secchi – WNS2

  13. Otcl Interface main parameters • A single system-wide Allocator is installed in a terminal: set alc [$ter install-allocator Allocator/Proportional] • One Requester is installed into each terminal: set req [$ter install-requester Requester/RDBC] • The definition of Requester and Allocator must specify the subclass of the objects. The object name can be used at run time to dynamically change the properties of Allocator and Requester • The MAC/TDMA block is created through the procedure node-config consistently with the standard ns-2 procedure and configured through a set of class parameters Raffaello Secchi – WNS2

  14. Example: RBDC Requester • A generic rate- and volume-based request: where R(t) is the mean incoming traffic rate and q(t) is the incoming queue length at the requesting terminal • This expression can be interpreted as a proportional-integral controller of output rate (q(t) being the integral part), which improves the stability of the queue • Stability can be further improved by providing a minimum share to each station in addition to the requested bandwidth Raffaello Secchi – WNS2

  15. Test-bed platform for validation DVB-RCS DVB-S LAN Ethernet LAN Ethernet testbed specifications • Medium Access Control TDMA/TDM • The bandwidth allocation uses a DAMA scheme • It implements a variant of Rate Based Dynamic Capacity (RBDC) Raffaello Secchi – WNS2

  16. Throughput Comparison (ON/OFF traffic) Raffaello Secchi – WNS2

  17. Delay Comparison (ON/OFF traffic) Raffaello Secchi – WNS2

  18. We described Tdma-dama, a simulator of TDMA satellite MAC based on ns-2 that allows investigation of a large class of DAMA schemes, including those outlined in the DVB-RCS standard We validated the simulator through measurements performed on the Skyplex Data network, which implements a variant of the RBDC allocation mechanism The statistics considered were throughput and one-way delay The simulator was able to accurately reproduce the dynamics of the real system The simulations highlight that DAMA algorithms are responsible for the large delay (several times the propagation delay) that may occur in response to abrupt variations of input rate Conclusions Raffaello Secchi – WNS2

  19. The software is provided under a MIT free software license http://votos.isti.cnr.it/simulator.htm How to get the software? Raffaello Secchi – WNS2

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