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ATM-Sat

Intersatellite Link (ISL) Networks:Topological Design, Routing and

Network Dimensioning

Anton Donner

DLR Oberpfaffenhofen

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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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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