architecture of a space communications network simulator for

FSS workshop – October 2014

Architecture of a network simulator for Federated Satellite Systems:

Testing Mobile Ad-hoc Network protocols in FSS

Ignasi Lluch

Network layer

Communications layer

Optical link budget

modelRadio link budget

Overview: A suite of tools for FSS feasibility

analysis/ Preliminary design at SIRG

Loosely integrated but compatible toolbox

Network simulator

modelRadio link budget

model

Oct 2014 |

Orbit layerOrbital propagator, node positions(t)

S/C layer

ACDSPower

FSS P/L

FSS simulation toolkit

Orbital Optimization tool

Comms

S/C layer

ACDSPower

FSS P/LComms

Resource balancing

model

� 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

Existing network simulation tools

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 |

Network simulator architecture (I)

� Nodes can be

spacecraft or ground

stations

� FileManager object

performs memory

management and

Oct 2014 |

management and

content partitioning

� FileManager hosts a

processor and a

linkControl object…

Network simulator architecture (II)

� FileManager can

operate a ISL or a

Space-to-Ground

link independently

� Network layer

Oct 2014 |

Network layer

protocol

implemented at

processor object,

Transport at

FileManager, Data

link at linkControl.

Message processing

Oct 2014 |

Main runtime

Oct 2014 |

FSS network characteristics

� Network Latency from moderate to significant (GEO-LEO)

� Connectionless: Story-carry-forward concept

� Data-centric (no real time VoIP)

Oct 2014 |

� Dynamic but predictable topology

� Unpredictable availability

Mid way betweenMobile ad-hoc networks(MANET) TCP/IP overSat in dedicatedconstellations

FSS is a semi-sparse network (2D-3D)

A

B

C D

KL

Oct 2014 |

M

E

F

G

H

I

J

KL

Data link layer:SDMA

� All comms point-to-point, low-interference baseline.

� More complex interference control schemes can be addedon top (Code Division).

I.Node A on ‘listening’ RX mode II.Incoming carrier sensed III. RX Gain directionality

Oct 2014 |

A A A

TX always directional (topology known)

B

Rejection condition

Network layer: Discovery process

� ‘Active’ Discovery: ‘hello’ messages containing NetworkState Knowledge (NSK) sent on randomized slots whennode is available and not committed.

� Based on OSLR concept (optimized state link routing)

Node A is available and draftsahead a discovery plan:

Notional NSK matrix

Oct 2014 |

A

B

C

?

?

ahead a discovery plan:

� Send ‘hello’ message withNSK to B at t0

� Wait for a random time slot

� Send ‘hello’ message withNSK to B at time t2

�� 0 ? ?

�−1

�

Network routing

� Recurrent routing of content files at each node: at everyhop, the current node re-thinks the routing with its ownNSK.

� Store carry and forward, ‘the file your received is nowyour problem’

� what is the best next hop possible?

Oct 2014 |

� what is the best next hop possible?

� Open Shortest Path First with topology Prediction andweights based on link availability expectation: aninterpretation of mobile ad-hoc proactive routing protocols

[BATMAN/OSLR ]

Content delivery

� Apart from network discovery messages, contentmessages (files attached) are sent over an open channel:Requires Initial + final acknowledgements within timewindows.

A B

Oct 2014 |

Request-to-Send (RTS)

Clear-to-Send (CTS)

Acknowledgment

tim

eout

Init content TX

Notify Reception - close channel

Tim

eout=

rate

+w

indow

tim

eout

� Data link layer : SDMA.

� Network layer: autonomous network discovery, (OSLR-like). Descentralized Recurrent routing (BATMAN-like) withSPF over link expectation availability weights, futuretopologies

� Transport: selective (minimal) acknowledgement strategy,

Network protocol summary

� Transport: selective (minimal) acknowledgement strategy,over short file size (DTN/saratoga concepts)

� Supports predictable topologies with random nodeavailability ->quasi stochastic network state

� Let’s simulate it!

Oct 2014 |

Simulation results

� 40 LEO satellites/ 9 ground stations scenario.Heterogeneous ground link capacity.

� Each SC generates data in random uniform distributions

� 1 day simulation, no usage of FSS:

Oct 2014 |

� Uniform file latencydistribution with 41min average

Simulation results

� 40 LEO satellites/ 9 ground stations scenario


� 1 day simulation, 40% average node availability:

Oct 2014 |

� File latencyaverage improvesto 24 min (-17min)

Simulation results

� 40 LEO satellites/ 9 ground stations scenario


� 1 day simulation, 70% average node availability:

Oct 2014 |

� File latencyaverage improvesto 11 min (-30min)

THANKS!

Oct 2014 |

BACKUP

Oct 2014 |

Simple Example of Routing

A

B

C

D

E

� A File is sent from A and has to reach the ground (E)

NSK knowledge at node A

current time t5

Oct 2014 |

� The graph is explored step by step and weights assigned toedges. How?

Graph exploration step 1

A

B D

E

NSK knowledge at node A

current time t5

1.1) Find nodes in view from A at t5 (pure geometry)

C

Oct 2014 |

C

1.1) Find nodes in view from A at t5 (pure geometry)

1.2) Assign weights based upon NSK-> more uncertain routesdisfavored, recently active nodes promoted [3 MRU]

AB

WAB

WAC


A

B D

E

Nodes explored list : A

1.1) Find nodes in view from B, and then C, at t6 (future top.)

C

Oct 2014 |

C

1.1) Find nodes in view from B, and then C, at t6 (future top.)

Do not trace back to nodes already explored (A)

1.2) Assign weights based upon A’s NSK

AB

WAB

WAC

DWBD

WBC


A

B D

E

Nodes explored list :

A,B,C

1.1) Find nodes in view from D t7 (future top.)

A’s

C

Oct 2014 |

C

1.2) Assign weights based upon A’s NSK (ground stationcontributes 0 and has default connection to network sink)

AB

WAB

WAC

DWBD

WBC E

WBE

FILE

SINK

Shortest path

� Keep exploring until all nodes are in the list or no more newnodes are in view

� Solve graph by OSPF (Dijkstra)

� This returns best candidate for next hop (route most likely towork)

� Eliminate from graph and Proceed again to find second best

Oct 2014 |

� Eliminate from graph and Proceed again to find second bestcandidate (ordered candidate list)

C

AB

WAB

WAC

DWBD

WBC E

WBE

FILE

SINK1

Data link layer: implementing SDMA

� Practical implementation of this Omni / directional Rx Txcould be done by:

� Beamforming array(s)

� Omni Rf beacons + optical link (recent NASA Glenndevelopment [1])

Oct 2014 |

Ground

Network layer: Discovery process

AB Received at t1. B updates its NSK. Colum D

is updated if t(D)new knowledge >t(D)old

knowledge

t TX

t0 TX

Oct 2014 |

Ct2 TX

Received at t3. C updates its NSK.

Disregards info about D

� I say ‘hello, I am up, and this is what I know’ to othernodes in hope they are doing the same

� Knowledge is stored as ‘last time somebody knewsomething of that node’

architecture of a space communications network simulator for

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