Internetworking with satellite constellations PhD viva presentation Centre for Communication Systems Research, University of Surrey 11am, Wednesday, 21 February 2001. Lloyd Wood http://www.ee.surrey.ac.uk/Personal/L.Wood/ work done in the Networks Group, Centre for Communication Systems Research, University of Surrey.
Overview of this talk and Lloyd’s PhD work: • Geometry; orbital constraints, mesh network topology, handover and routing give path delays across constellation. • TCP across LEO/MEO mesh networks – performance influences the approach to routing design. • Multicast – a simple core-based approach; place the core (and its network state), shape the resulting tree. • Controlled handover in rosette geometries for classes of service with smaller path delay variation. • Architecture – support IP QoS and multicast using MPLS for a single control plane. Internetworking with satellite constellations - Lloyd Wood 2
Without intersatellite links With intersatellite links (ISLs) Satellites are just ‘last hop’ . Satellites aren’t just ‘last hop’ . Users need to be in same satellite Users don’t need to be in same footprint as gateway station for satellite footprint as gateway station connectivity. for connectivity. Coverage over remote areas (oceans) Coverage over remote areas (oceans) where there is no local infrastructure where there is no local infrastructure not possible. possible. Physical delay within space segment Physical delay within space segment highly predictable and small; depends highly variable but deterministic; depends entirely on terminal-satellite-gateway hops on where terminals and gateways are, path during passes; likely to be symmetrical. between them. May not be symmetrical. Delay in ground segment unknown . Can neglect ground segment. Resulting total delay unknown . Can model space segment, find delay. Onboard processing, switching are Onboard processing, switching, routing optional . No onboard routing. are necessary . It’s a network. example constellations: example constellations: Globalstar, ICO, Skybridge Iridium, Teledesic, Spaceway Internetworking with satellite constellations - Lloyd Wood 3
Concentrated on the satellite constellation with ISLs • It’s a single network. An autonomous system; single point of control and management (not a military viewpoint). • Constraints of orbital motion and coverage mean that network can be defined and simulated with accuracy. • Speed of light is a constraint. ISL propagation delay is largest factor, subsuming all others. • What does traffic across the constellation experience? How do applications see it? Focus on delay perspective. Latency indicates performance. (Congestion is multivariable; too many starting assumptions required to simulate congestion accurately.) Internetworking with satellite constellations - Lloyd Wood 4
Constellation geometry - star vs rosette (LEO/MEO ISL designs) 1r −150 150 −150 150 1q 2q 12t 1p 2p 12u 2e 2o 1o 12v 3q 11u 12s 3d 3p 11v 11t 2r 3r 2n 12w 1n 3o 11w 2m 12x 1a 3n 1m 11x −120 120 −120 4p 10u 120 4q 10t 4o 10v 2l 12a 3m 11a 4n 10w 1l 1e 4m 10x 3l 2k 12b 11b 1k 4l 10a 3c 5p 9v 5q 5o 3k 11c 9w 9u 2j 12c 5n 4k 10b 9x 2d 5m 1j 9a 3j 11d 4j 10c 5l 9b 2i 12d 4b 5k 9c 9t 10s 5r 4i 1i 3i 11e 10d 4r 5j 9d 4c 6o 6n 6m 8x 8w 8v 2h 12e 6l 8a 1b 6p 6k 8b 8u 5i 4h 10e 9e 6j 8c 3h 11f 1h 6i 8d 5h 9f 6h 8e 4g 10f 2g 12f 6q 6g 8f 8t 7i 7h 7g 5g 7f 7e 7k 7j 9g 6f 7d 7c 7l 8g 11g 3g 7b 2a 4a 7m 8h 1g 6e 7a 90 10g 4f 7n 9h 5f 7x 90 −90 −90 6d 0 N 7o 8i 12g 2f 7w −60 −30 30 60 0 N S 1s −60 −30 30 60 S 8j 11h 3f 5e 6c 9i 4e 7p 10h 7v 8k 1f 6b 3b 9j 5d 8l 2e 6a 12h 2c 3e 4d 7u 7q 10i 11i 8m 9k 5c 6x 1e 2b 6w 8n 4c 10j 12i 2d 5b 9l 11j 3d 6v 8o 4d 9m 1d 5a 10k 4b 2c 11k 12j 3c 7t 8p 6u 1c 7r 9n 5x 8s 10l 4a 1c 6r 3b 11l 12k 2b 5w 9o 3e 10m 4x 6t 8q 1b 3a 5v 9p 11m 12l 2a 11s 10n 4w 3a 1a −60 60 11n 3x 2x 5u −60 3s 9q 12m 60 10o 4v 1x 1d 3w 11o 2w 12n 10p 4u 1w 4e 3v 11p 5t 9r 2v 12o 6s 4t 8r 10q 1v 11q 2u 3u 12p 1u 9s 5s 1t 12q 2t 12r −30 30 2s 3t 11r −30 30 4s 10r Background map rendered by 7s Background map rendered by Hans Havlicek (http://www.geometrie.tuwien.ac.at/karto/) 0 Hans Havlicek (http://www.geometrie.tuwien.ac.at/karto/) 0 Teledesic (Boeing design - 288 active satellites) Hughes Spaceway NGSO (20 active satellites) c. Teledesic LEO satellite network (Boeing 288-satellite design, optimised coverage), showing simulated ground terminals b. Spaceway NGSO MEO satellite network with ISLs at a point in time, showing simulated ground terminals descending satellites (moving south) ascending satellites (moving north) ascending (moving north) and descending (moving south) satellites overlap 90 90 7g 9g 11g 1g 3g 5g 4g 12f 6g 8g 10g 12g 2f 4f 6f 8f 2g 10f seam 3h 5h 7h 9h 11h 1f 3f 5f 7f 9f 1h 11f 2h 4h 6h 8h 10h 12h 2e 4e 6e 8e 10e 12e 3i 5i 7i 9i 11i 1e 3e 5e 7e 9e 11e 1i 60 60 3b 4b 1b 2b 2i 4i 6i 8i 10i 12i 2d 4d 6d 8d 10d 12d London 3j 5j 7j 9j 11j 1d 3d 5d 7d 9d 11d 1j London 2j 4j 6j 8j 10j 12j 2c 4c 6c 8c 10c 12c Tokyo 3k 5k 7k 9k 11k 1c 3c 5c 7c 9c 11c 1k Tokyo 30 2c 3c 4c 1c 30 2k 4k 6k 8k 10k 12k 2b 4b 6b 8b 10b 12b unprojected latitude unprojected latitude 1b 3b 5b 7b 9b 11b 3l 5l 7l 9l 11l 1l 2l 4l 6l 8l 10l 12l 2a 4a 6a 8a 10a 12a 3a 4a 1a 2a 1m 3m 5m 7m 9m 11m 1a 3a 5a 7a 9a 11a 0 0 2m 4m 6m 8m 10m 12m 2x 4x 6x 8x 10x 12x Quito Quito 1n 3n 5n 7n 9n 11n 1x 3x 5x 7x 9x 11x 2n 4n 6n 8n 10n 12n 2w 4w 6w 8w 10w 12w 1o 3o 5o 7o 9o 11o 1w 3w 5w 7w 9w 11w 1d 2d 3d 4d -30 -30 2o 4o 6o 8o 10o 12o 2v 4v 6v 8v 10v 12v 1p 3p 5p 7p 9p 11p 1v 3v 5v 7v 9v 11v 4e 1e 2e 3e 2p 4p 6p 8p 10p 12p 2u 4u 6u 8u 10u 12u 1q 3q 5q 7q 9q 11q 1u 3u 5u 7u 9u 11u -60 -60 2q 4q 6q 8q 10q 12q 2t 4t 6t 8t 10t 12t 1r 3r 5r 7r 9r 1t 11r 3t 5t 7t 9t 11t 2r 4r 6r 8r 2s 10r 4s 12r 6s 8s 10s 12s seam 1s 3s 5s 7s 9s 11s -90 -90 -180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180 -180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180 unprojected longitude unprojected longitude Internetworking with satellite constellations - Lloyd Wood 5
Intersatellite links give us mesh networks... path delay (milliseconds) over a day 0.600 Shortest-path propagation delay time (seconds 0.500 0.400 orbital seam orbital plane - breaks these ISLs constant intraplane ISLs maintained 0.300 0.200 highest latitude 0.100 ascending 0.000 Time 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 satellites (hours) and as number of hops through the mesh: highest latitude 1 4 1 3 1 2 1 1 Nu m b er o f wir el es s lin k s ( h op s ) t ra ve rs ed 1 0 descending 9 satellites 8 7 6 5 4 interplane ISLs - 3 2 variable length 1 ‘Twisted Manhattan’ 0 0 1 2 3 4 5 6 7 8 9 1 0 11 1 2 1 3 14 1 5 16 1 7 1 8 19 2 0 2 1 22 2 3 satellite network variant T Im e (h o ur s ) Path delay from Quito to London (by LEO/MEO/GEO ) ...and orbital motion gives us handover, path delay variation. Internetworking with satellite constellations - Lloyd Wood 6
So, taking path delay further… Del ay b e tween terminals o n th e equ ator acro ss sea med Tel edesic 90 14 0 so lid bar i s del ay range f ro m max to mi n e rror b ar sh ows o n e sta ndard d eviatio n av era g e d ela y 60 12 0 tota l pr opa gati on delay seen a cr oss n etw ork p ath (m s) 30 unprojected latitude 10 0 angle of separation between terminals 0 fixed 8 0 range over which one terminal is moved −30 6 0 −60 4 0 −90 −180 −150 −120 −90 −60 −30 0 30 60 90 120 150 180 2 0 unprojected longitude Teledesic with and without 0 0 1 0 20 3 0 4 0 5 0 6 0 7 0 8 0 9 0 10 0 11 0 12 0 13 0 14 0 1 50 16 0 17 0 18 0 angle of se p ara ti on in longitude betw een t erm ina ls ( degrees) cross-seam links; every line D e la y b e tw ee n te rm in als o n e qu a tor a cro s s T e le d es ic wi th c ro ss -s ea m link s 1 40 s olid b a r is de l a y ra ng e f ro m m a x to m in e rror b a r sh o ws o ne s t anda r d d ev iat i o n av e ra ge de lay shows a 24-hour simulation at 1 20 to t a l pro p a ga ti on d e l ay s e en o v er n e tw o rk p a th ( m a given latitude separation 1 00 between terminals. 80 60 Smaller delays and delay 40 variation with cross-seam links. 20 Note difference at 0º separation. 0 0 10 2 0 3 0 4 0 50 60 70 8 0 9 0 1 00 1 10 1 2 0 13 0 14 0 150 1 60 1 70 18 0 a n gle o f s ep ar atio n in lo n g itu d e bet w ee n te r m in a ls (de gr ee s) Internetworking with satellite constellations - Lloyd Wood 7
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