intersatellite link (isl) networks: topological design ... · anton donner atm-sat workshop, 19...
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ATM-Sat Workshop, 19 Juni 2002, Berlin KN-DNAnt
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ATM-Sat
Intersatellite Link (ISL) Networks:Topological Design, Routing and
Network Dimensioning
Anton Donner
DLR Oberpfaffenhofen
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ATM-Sat
4 Which ISL network topology ?
h from the Iridium heritage to a modern (sustainable) design !
4 “ATM-based“ ISL routing concept:
h a discrete-time dynamic routing framework derived from core ATMprinciples rather than an ATM implementation !
4 Integrated ISL routing and network dimensioning
4 Conclusions on work done
4 Ongoing work and extensions
Outline of ISL Research within ATM-Sat
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ISLs and ATM-Sat
4 No “early-to-market“ strategy, but strategic project ...
4 ... consequently re-defining or just recalling the orientation/direction:
h “friendly“ scenarios: – high-capacity multicast– fixed terminals– aggregated traffic ...
h prospective markets: – high quality Internet– particular global VPNs– high-speed and reliable global information distribution– trunking market niches ...
h driving technologies: – MPLS– optical networking– λ switching ...
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Scenario
Space segment:ISL trunk network
Earth segment: Wireline backbones
Air interface:OD traffic
ISLSubnetwork
ATM, IPUp/Downlink:- Handover- Sat. Diversity
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The Inclined Walker “Delta“ Constellation M-StarConstellation:
regular phasing, phasing factor 5absolute symmetry of the orbital constellationno "seam" like in polar constellations
orbit altitude 1350 kmorbit period 113 min# of satellites 72# of orbits 12inclination 47°
Planar projection (schematic):
M-Star utilizes the promising combination of “delta“ constellation pattern and optical ISLs
Equator
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North Pole
South Pole
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Orbits
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Reference ISL Topology for M-Star
Snapshot at t=0:
All links are permanently maintained over the whole orbit period !
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Discrete-Time Dynamic Routing FrameworkOff-line Routing Framework
t=T-∆t s=S-1
t=∆t s=1
t=0 s=0Instantaneous
Virtual Topology Setup I-VTS(s)
t=2∆t s=2
Discrete-Time VirtualTopology Design DT-VTD
(1,2)
(1,3)
(N-1,N)
K Shortest Path Search
KSPA
OD pairs∀
ProcessingOD)(kK →
flexible k , path grouping / path reordering
Topological DesignPermanent Physical Topology Design P-PTD
Topological design of ISL networkwith permanent (non-switched) physical links
Topological design of ISL networkwith permanent (non-switched) physical links
for Walker delta constellations
Capacity DimensioningDiscrete-Time Multi-Step Dimensioning DT-MSD
Single-stepdimensioning
+ post-processing
Linkedsingle-step
dimensioning
Multi-stepdimensioning:
Dynamic optimiz.
or or
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Network Dimensioning: Target Functions
ISL capacity requirements
Bandwidth & RF power
Satellite capacity requirements
Processing power & buffer sizes
DC power
Size & weight of satellite System costs
positive “side effect“: better utilization of installed network capacity
Candidate target functions: TF1: Minimize worst case link (WCL) load
TF2: Minimize worst case node (WCN) load
LEO constellation dynamics --> every sat/link encounters worst case sometime--> all sats/links to be dimensioned accordingly
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Performance of Isolated Step Optimization from here, all numerical examples assume network-uniform traffic,i.e., a normalized symmetric traffic load of 1 between all OD pairs
Worst Case Link (WCL) Load: EqualSharing - BoundedOptimization - FullOptimization
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... and all that on the map:without optimization (shortest path routing):
with optimization (multipath/alternate routing):
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Conclusions (on Work Done)
Network design process for LEO ISL networks:
Topological design of ISL segments with permanent link feature
Discrete-time dynamic routing framework based on VPCs
Network dimensioning: (a) heuristic design rules, (b) linear programming optimization approach
(a) + (b) = efficient solution of routing/dimensioning taskgood performance
Considerable reduction of worst case link loads can be achieved atthe expense of an acceptable increase in both,
- average link loads- average path delays
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Possible Extensions (1):Multi-Protocol Label Switching (MPLS)
4 A way to integrate ATM and IP, combining the benefits
4 Appeal of and issues for MPLS-based ISL networking
hMPLS is a technique dedicated to backbones
h a “blue-sky“ ISL network may be an ideal basis to exploit the full potential of MPLS in a homogeneous global MPLS domain
h importance of traffic engineering; potential use of proposed dimensioning methods, alternate routing approaches ...
h each satellite acts as edge router (serving ground) and core router (transit)
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A simple MPLS network
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Label Switching Router (LSR)
Label Edge Router (LER)
Ingress LER
Egress LER
Egress LER
Label Switched Path (LSP)
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BackboneNetwork
PacketLabelPacket
Label
TerrestrialNetwork
AccessNetwork
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Possible Extensions (2): Optical ISL Networking
4 Key role of optical communications for current/future backbone networks
h (D)WDM - (dense) wavelength division multiplex
h wavelength-routing or λ-switching
h form optical transport network (OTN) by circuit-switched lightpaths
4 For future ISL backbones:
h low mass, size and power consumption of optical ISL terminals
h PAT requirements for inter-plane ISLs can be met by laser technology
h space OTN concepts are really close to the developed connection-oriented routing and dimensioning framework
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