Architecture of a network simulator for Federated Satellite Systems: Testing Mobile Ad-hoc Network protocols in FSS FSS workshop October 2014

Transcription

1 Architecture of a network simulator for Federated Satellite Systems: Testing Mobile Ad-hoc Network protocols in FSS FSS workshop October 2014 Ignasi Lluch

2 Overview: A suite of tools for FSS feasibility analysis/ Preliminary design at SIRG Loosely integrated but compatible toolbox Network layer Network simulator Communications layer Optical link budget model Radio link budget model S/C layer Orbit layer Orbital propagator, node positions(t) S/C layer FSS simulation toolkit Orbital Optimization tool Power ACDS Power ACDS Resource balancing Comms FSS P/L Comms FSS P/L model Oct 2014 Page 2

3 Existing network simulation tools NS3 and Omnet++ with manet pluguin: Slow learning curve, too detailed at this stage, no out-of-the-box functionality for space networks Qualnet(propietary) Astrolink(Google/NASA developed using STK) presented in AIAA San Diego 2014 In-house tool in matlab: Rest of our tools in matlab/java. Integration with Pricing work (U.Pica) Total control Matlab supports OOP and callback on event. Oct 2014 Page 3

4 Network simulator architecture(i) Nodes can be spacecraft or ground stations FileManager object performs memory management and content partitioning FileManager hosts a processor and a linkcontrol object Oct 2014 Page 4

5 Network simulator architecture(ii) FileManager can operate a ISL or a Space-to-Ground link independently Network layer protocol implemented at processor object, Transport at FileManager, Data link at linkcontrol. Oct 2014 Page 5

6 Oct 2014 Page 6 Message processing

7 Oct 2014 Page 7 Main runtime

8 Oct 2014 Page 8 Main runtime

9 FSS network characteristics Network Latency from moderate to significant(geo-leo) Connectionless: Story-carry-forward concept Data-centric(no real time VoIP) Dynamic but predictable topology Unpredictable availability Mid way between Mobile ad-hoc networks (MANET) TCP/IP over Sat in dedicated constellations Oct 2014 Page 9

10 FSS is a semi-sparse network(2d-3d) B A C D K J L E M I H G F Oct 2014 Page 10

11 Data link layer:sdma All comms point-to-point, low-interference baseline. More complex interference control schemes can be added on top(code Division). I.Node A on listening RX mode II.Incoming carrier sensed III. RX Gain directionality A A A Rejection condition TX always directional (topology known) B Oct 2014 Page 11

12 Network layer: Discovery process Active Discovery: hello messages containing Network State Knowledge (NSK) sent on randomized slots when node is available and not committed. Based on OSLR concept(optimized state link routing) Notional NSK matrix 0?? A 1 C B?? NodeAisavailableanddrafts ahead a discovery plan: Send hello message with NSKtoBatt0 Waitforarandomtimeslot Send hello message with NSKtoBattimet2 Oct 2014 Page 12

13 Network routing Recurrent routing of content files at each node: at every hop, the current node re-thinks the routing with its own NSK. Store carry and forward, the file your received is now your problem whatisthebestnexthoppossible? Open Shortest Path First with topology Prediction and weights based on link availability expectation: an interpretation of mobile ad-hoc proactive routing protocols [BATMAN/OSLR] Oct 2014 Page 13

14 Content delivery Apart from network discovery messages, content messages (files attached) are sent over an open channel: Requires Initial + final acknowledgements within time windows. A B Request-to-Send (RTS) timeout Init content TX Timeout= rate+window Clear-to-Send (CTS) Acknowledgment timeout Notify Reception - close channel Oct 2014 Page 14

15 Network protocol summary Datalinklayer:SDMA. Network layer: autonomous network discovery, (OSLRlike). Descentralized Recurrent routing(batman-like) with SPF over link expectation availability weights, future topologies Transport: selective (minimal) acknowledgement strategy, over short file size(dtn/saratoga concepts) Supports predictable topologies with random node availability->quasi stochastic network state Let s simulate it! Oct 2014 Page 15

16 Simulation results 40 LEO satellites/ 9 ground stations scenario. Heterogeneous ground link capacity. Each SC generates data in random uniform distributions 1daysimulation,nousageofFSS: Uniform file latency distribution with 41 min average Oct 2014 Page 16

17 Simulation results 40 LEO satellites/ 9 ground stations scenario Each SC generates data in random uniform distributions 1 day simulation, 40% average node availability: File latency average improves to24min(-17min) Oct 2014 Page 17

18 Simulation results 40 LEO satellites/ 9 ground stations scenario Each SC generates data in random uniform distributions 1 day simulation, 70% average node availability: File latency average improves to11min(-30min) Oct 2014 Page 18

19 THANKS! Oct 2014 Page 19

20 BACKUP Oct 2014 Page 20

21 Simple Example of Routing AFileissentfromAandhastoreachtheground(E) NSK knowledge at node A current time t5 A B C D E Thegraphisexploredstepbystepandweightsassignedto edges. How? Oct 2014 Page 21

22 Graph exploration step 1 NSK knowledge at node A current time t5 A C B D E 1.1)FindnodesinviewfromAatt5(puregeometry) 1.2) Assign weights based upon NSK-> more uncertain routes disfavored, recently active nodes promoted[3 MRU] A WAB WAC B C Oct 2014 Page 22

23 Graph exploration step 2 Nodes explored list : A B D C A E 1.1)FindnodesinviewfromB,andthenC,att6(futuretop.) Donottracebacktonodesalreadyexplored(A) 1.2) Assign weights based upon A s NSK A WAB B WBC WBD D WAC C Oct 2014 Page 23

24 Graph exploration step 3 Nodes explored list : A,B,C A B D C E 1.1)FindnodesinviewfromDt7(futuretop.) 1.2) Assign weights based upon A s NSK (ground station contributes 0 and has default connection to network sink) A WAB WAC B C WBC WBD D WBE E FILE SINK Oct 2014 Page 24

25 Shortest path Keepexploringuntilallnodesareinthelistornomorenew nodesareinview Solve graph by OSPF(Dijkstra) Thisreturnsbestcandidatefornexthop(routemostlikelyto work) EliminatefromgraphandProceedagaintofindsecondbest candidate(ordered candidate list) A WAB WAC B C WBC WBD D WBE E 1 FILE SINK Oct 2014 Page 25

26 Data link layer: implementing SDMA Practical implementation of this Omni / directional Rx Tx couldbedoneby: Beamforming array(s) Omni Rf beacons + optical link (recent NASA Glenn development[1]) Ground Oct 2014 Page 26

27 Network layer: Discovery process A t0tx B Receivedatt1.BupdatesitsNSK.ColumD is updated if t(d)new knowledge >t(d)old knowledge t2tx C Oct 2014 Page 27 Received at t3. C updates its NSK. Disregards info about D I say hello, I am up, and this is what I know to other nodesinhopetheyaredoingthesame Knowledge is stored as last time somebody knew something of that node