Architecture Issues for Integrated Space and Terrestrial ... · PDF fileArchitecture Issues...

LIDSLIDS

1vincent chan september 2004 Laboratory for Information and Decision Systems

Architecture Issues for Integrated Space and Terrestrial Networks

Vincent W. S. Chan

Laboratory for Information and Decision SystemsDepartment of Electrical Engineering and Computer Science

Department of Aeronautics and AstronauticsMassachusetts Institute of Technology

LIDSLIDS


PROCESSINGCENTERS

SENSOR

CONUS

TERRESTRIALNETWORK

TRANSOCEANIC LINK

COMMCOMM

ULTRA-FASTLAN

CPU

CPUGATEWAY

MEDIABANK

GATEWAY

CPU

LOCALINFRASTRUCTURE

TACTICALAIR SUPPORT

WIRELESSLAN COMMAND

POST

SURVEILLANCEAIRCRAFT / UAV

PROCESSINGCENTERS

PROCESSINGCENTERS

SENSOR

CONUS

TERRESTRIALNETWORK

TRANSOCEANIC LINK

SENSOR

CONUS

TERRESTRIALNETWORK

TRANSOCEANIC LINK

COMMCOMM

ULTRA-FASTLAN

CPU

CPUGATEWAY

MEDIABANK

GATEWAY

CPU

COMMCOMM

ULTRA-FASTLAN

CPU

CPUGATEWAY

MEDIABANK

GATEWAY

CPU

LOCALINFRASTRUCTURE

TACTICALAIR SUPPORT

WIRELESSLAN COMMAND

POST

LOCALINFRASTRUCTURE

TACTICALAIR SUPPORT

WIRELESSLAN COMMAND

POST

SURVEILLANCEAIRCRAFT / UAV

Robust Dynamic Tactical Networkssupport 10-500k communicating devices in theater

• Beyond traditional "tactical" which is voice/human user oriented

• High reliability delivery• Beyond traditional ad-hoc

networks

LIDSLIDS


Spaceuser

Spaceuser

Spaceuser

Space backbone (Lasercom)

Terrestrial backbone (fiber)

RF

RF Airborne

Ground radio

Accessnetwork

user

Network topology

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•Ultra-long propagation delays

•Software delays

•Large delay-bandwidth product•Many packets in flight

•Time-varying channel•Capacity

•Symbol-size•Code-rates

•Fading •outage•block erasures

•Dynamic connectivity (unpredictable)•Multiple connectivity •Changing channel quality

•Pol., linear and nonlinear distortions

d

dd

d d

L

LL

L

T

T T

T

D

D

D

DT

S

S S

Network properties

n L

LIDSLIDS


NetworkDLCPhysical

G

G

G Gateway Wireless Fiber Satcom 1 Satcom2

Appl

Mod/DemodVariable R FEC ARQ

Media AccessControl Router/Buffer

Transport

Net Management

•Dynamic routing: deterministic & stochastic•Heterogeneous network: Satcom, fiber, wireless•Differentiated services: cost-based, time-deadline, ...

•Dynamic rate allocation•Agile beams•MAC

Congestion& FlowControl

Gateways

Convergence Layer

-----------------Agent-

Mediator

•Joint application-network coding•Policy networking

Dynamic 4-D Network

LIDSLIDS


Critical architecture issues1. Physical topology

2. Modulation and codinga. Lasercomb. RF trunkc. RF AJ accessd. RF ground radio

3. Media access control protocol (MAC) RF, Lasercom

4. Network routing hardware and protocol

5. Transport Layer protocol

6. Network management and control

7. Source coding (interactions with others)

8. Internetworking

9. Security (not just crypto)

LIDSLIDS


S/C node: Processing + MAC + switching + routing

Opticalcross-

connect

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Number of Nodes (N)

Cos

t [ $

M ]

Number of Nodes (N)

Cos

t [ $

M ]

•Uniform & hub traffic

•% pass-thru traffic increases with N

•Degree 3, 4 seems best

•Mesh is better: asymmetric traffic will have more dramatic effects

Ring (U) Circulant (U) Circulant (H+u)

Constellation connection topology

One architecture does not fit both traffic patterns

LIDSLIDS


Media Access Control (MAC) Protocol

•Efficient use of satellite resources (e.g. receivers, xmitters)•MAC protocol critical for efficient performance

oRandom access ? oScheduling for larger transactions oAccess delay of several roundtrips will have significant interactions with TCPoOpen air interface security

IF

DecoderDemod

Coder

Router

ModPA

IFFilter

IF D/A

Vec

tor

Proc

esso

rDecoderDemod

Coder

Router

ModIFAϕPA

MBA

ϕ-array

IF

DecoderDemod

Coder

Router

Mod

DecoderDemod

Coder

Router

ModPA

IFFilter

IF D/A

Vec

tor

Proc

esso

rDecoderDemod

Coder

Router

Mod

DecoderDemod

Coder

Router

ModIFAϕPA

MBA

ϕ-array

LIDSLIDS


Clear Lightrain

Moderaterain

Heavyrain

0-3 db 3-7db 7-20 db >20 db

Clear Lightrain

Moderaterain

Heavyrain

0-3 db 3-7db 7-20 db >20 db•Highly variable channel

•Rain attenuation•Turbulence scintillation

•Adaptive modulation and coding•Adaptive signal constellation•Variable coding rate•Interleaving•Diversity combining (rake-like) •Trellis coding at lower code rates•Fiber optics codes not appropriate

•May use ARQ to get better reliability performance

•Variable capacity, long delays, large bandwidth-delay product not previously encountered in terrestrial networks – will have significant interactions with upper layers, severe performance degradation possible

RF space-ground links

LIDSLIDS


v

θ

v

θ

Boundary layer turbulence

Atmospheric turbulence

v

θ

v

θ

v

θ

v

θ

v

θ

Boundary layer turbulence

Atmospheric turbulence

v

θ

v

θ

v

θ

Atmospheric optical communication channel

SUB-APERTURES

Σ

DECISIONELECTRONICS

DATAOUT

ELECTRICALSIGNAL

COMBINING

APDFRONT ENDS

Non-outage

Outage

rate γ12

rate γ21

21

Non-outage

Outage

rate γ12

rate γ21

21

outage outage

Non-outage

Non-outage

Non-outage

outage outage

Non-outage

Non-outage

Non-outage

•0.1-10 mS fades – outages

•Interarrival time 1-100 mS

•FEC alone will require large interleaver

•Possibly combine with ARQ (delay)

•Diversity via multiple receiver or AO must be used

LIDSLIDS


TCP Window Flow Control & ThroughputW

indo

w si

ze W

•Outage creates window closing, slow start,...

•Window scale option only takes care of max window problem

•With almost an outage within each RTT, window will not build up – low thruput or assure no outage which is costly in link power

•Other fairness problems when mixed with terrestrial traffic

Short RTT

~1% Long RTT

11

For σχ=0.5, 1Gb/s link1 user

For σχ=0.5, 1Gb/s linkmany users

LIDSLIDS


Backbone

RF

Backbone

RF

Sink

•Dynamic adaptation based on channel states - variable link capacities and qualities; fast adaptations may lead to oscillations

•Maximizes downlink capacity and/or delay via optimum routing/scheduling

•End-to-end routing including terrestrial subnet

•Time deadline QoS

•Routing algorithm -OSPF ?, ..., Internetworking - BGP?, ...

•Security of Layer 3 network management and control

Network routing at Layer 3

LIDSLIDS


Backbone

RF

Backbone

RF

Packetswitch

Transport Layer Protocol – TCP, …?

•TCP is an end-to-end reliable delivery protocol

•If a long delay link does not make any errors, then window options can allocate unfair amount of resources

•If the long delay links have outages, then window flow control may prevent full rate transmissions, leading to very inefficient use of channel

•Proxy service decouples Layer 3 communication – hard to provide QoS such as time deadlines

•UDP plus add on protocol? Others?

LIDSLIDS


SharedProcessor

Backbone

RF

SharedProcessor

Backbone

RF

Interoperable distributed spacecom

•Interoperable spacecom, EHF, SHF, UHF, …, commercial•Data networking with packet switching and QoS (e.g. priority) in space•Serious internetworking issues•Security

LIDSLIDS


Security is crypto + denial of service + interception + locationInvolves: crypto + NM&C + all layers + interactions among layers

•Crypto•Proxy vulnerabilities

•TCP/IP vulnerabilities in open air•Traffic analysis

•Compromised routers - IP vulnerabilities,•Hardware vulnerabilities•Internetworking (BGPs)•Traffic analysis

•Interference with MAC, ARQ, FEC

•Jamming•Interception, location, ...•Intrusion entry point

Network security

LIDSLIDS


Phy

Net

DLC

TCP

Phy

Net

DLC

TCP

Cross-layer network attacks & mitigation

Window closing due to Physical-layer attack:TCP reacts poorly to jamming, closes windowReduces rate to < 1%

•Nulling•Rerouting•Change TCP

LIDSLIDS


Some observations1. Mesh/circulant constellation connection topology

2. Space-terrestrial links will have time-varying capacities, outages, ...

3. Non-stationary and large delay-rate-product channel properties impact Transport Layer protocol performance - TCP or not TCP for space, XCP?, UDP+?

4. Node switching hardware architecture important to be a right mix

5. Routing algorithm to optimize resources and adapt to channels with stability

6. Network management and control is a big issue, especially internetworking and security

7. Network architecture must last over 25 years, therefore

a. Not forever tied to a specific today standard

b. Upgradable protocols

c. Good for multiple generations of technologies

d. Pick an architecture trend that evolves

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