Architecture Issues for Integrated Space and Terrestrial ... · PDF fileArchitecture Issues for Integrated Space and Terrestrial Networks ... •Large delay-bandwidth product ... Mediator
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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
2vincent chan september 2004 Laboratory for Information and Decision Systems
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
3vincent chan september 2004 Laboratory for Information and Decision Systems
Spaceuser
Spaceuser
Spaceuser
Space backbone (Lasercom)
Terrestrial backbone (fiber)
RF
RF Airborne
Ground radio
Accessnetwork
user
Network topology
LIDSLIDS
4vincent chan september 2004 Laboratory for Information and Decision Systems
•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
5vincent chan september 2004 Laboratory for Information and Decision Systems
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
6vincent chan september 2004 Laboratory for Information and Decision Systems
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
7vincent chan september 2004 Laboratory for Information and Decision Systems
S/C node: Processing + MAC + switching + routing
Opticalcross-
connect
LIDSLIDS
8vincent chan september 2004 Laboratory for Information and Decision Systems
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
9vincent chan september 2004 Laboratory for Information and Decision Systems
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
10vincent chan september 2004 Laboratory for Information and Decision Systems
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
11vincent chan september 2004 Laboratory for Information and Decision Systems
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
12vincent chan september 2004 Laboratory for Information and Decision Systems
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
13vincent chan september 2004 Laboratory for Information and Decision Systems
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
14vincent chan september 2004 Laboratory for Information and Decision Systems
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
15vincent chan september 2004 Laboratory for Information and Decision Systems
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
16vincent chan september 2004 Laboratory for Information and Decision Systems
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
17vincent chan september 2004 Laboratory for Information and Decision Systems
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
18vincent chan september 2004 Laboratory for Information and Decision Systems
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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