TCP/IP Over LEO Satellites

1
TCP/IP Over LEO Satellites

• Related Activities within the ATM-Sat Project
• Presentation to Industry Representatives and
  Interested Scientists

2
Contents

• Test- Measurement Suite
• Global Set-Up
• Probe Station
• Simulation Environment
• First Simulation Results

3
Global Set-Up
Probe Station
Probe Station
4
Probe Station

• Consists of
• Workstation or PC running standard operating
  system
• FreeBSD
• Windows
• further OS possible
• Protocol performance testing tools (RFC 2398)
• Used as
• TCP analyzer
• User application platform

5
TCP Analyzer

• Fundamental Performance Evaluation
• Pre-defined set of experiments
• Automatic execution
• Base for comparing TCP flavors and network
  effects
• Configuration
• Operation System FreeBSD 4.1
• Testing Tools DBS, netperf, ...

6
User Application Platform

• Subjective QoS
• Set of daily life applications
• User interaction
• Supplementary performance evaluation
• Configuration
• Operation System Windows, Unix, ...
• Applications Web-Browsing, NFS, etc.
• Supplementary Tools tcptrace, tcpdump, ...

7
Where We Are ...

• Test- Measurement Suite ?
• Simulation Environment
• General Aspects
• System Parameter
• First Simulation Results

8
General Aspects

• Independence of demonstrator hardware
• Availabiltity only within final phase
• Isolate demonstrator (hardware) specifc side
  effects
• Unknown flavors of TCP
• Analysis of large networks
• Adaptation to emerging project constrains
• Simulation tool OPNET modeler / radio
• Industry prooven
• ATM support
• Satellite Orbits can be included
• Project specific aspects

9
System Parameters

• Satellite Orbit
• Bit Rates
• Bit Error Rate
• Up- Down-Link Delay
• Intra-Satellite Delay
• End-to-End Delay

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Satellite Orbit

• Slant Range
• Analytical model
• Function of orbit altitude
• Visibility constrains
• Analytical vs. Simulated Distance
• STK based simulation compared to theroy
• derivation less than 2

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Bit Rates
ISL 7 - 10 Gbit/s
Feeder Up Downlink32.768 Mbit/s
Service Downlink32.768 Mbit/s
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Bit Error Rate

• BER at target system above MAC
• Up- Down-Link
• Good weather condition 210E-8
• Rain
• causes link to collaps
• last for approx. 10 minutes
• on-off modell
• ISLs
• Limitations

13
Up- Down-Link Delay

• Based upon analytically gained distance
• Comparison analytical vs. simulated delay

14
Intra-Satellite Delay

• Final routes in the sky still open
• Assumed ISLs
• To forward and backward satellite
• To left and right neighbor
• Simulation based delays

15
End-to-End Delay

• Describes aspects of
• Routing behavior in the sky
• Intercontinental connections
• Cooperate networks
• Currently not considered
• Obtained through final simulations
• Reference measurements predict approx 150ms

16
Where We Are ...

• Test- Measurement Suite ?
• Simulation Environment ?
• First Simulation Results
• Link Model Description
• Link Model Verification
• RTT Measurement of TCP
• Future Steps

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Link Model Description

• Link
• Point-to-point
• Symmetrical or asymmetrical
• Wired
• Delay
• Function of time
• Deterministic, periodical
• Configurable Parameter
• BER
• Bit rate

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Link Model Verification

• Delay
• Expected values
• Consider queuing delay
• Bit rate
• Upper Limit

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RTT Measurement of TCP

• Impact of RTT-gain coefficient
• Acts as smoothing factor
• Considered values
• gain 0.125
• gain 1
• Results
• Derivation less than 1ms
• Smoothed curved closerto real round-trip
  delayvariation

20
Future Steps

• Timer granularity
• Effects of variable delay on throughput
• Switch to wireless link model
• Better BER model
• Simulation of large networks
• Include ATM-Sat MAC

21
World Wide Web

• http//www.fokus.gmd.de
• Information about FOKUS
• http//www.fokus.gmd.de/cats
• Information about the Competence Center CATS
• http//www.fokus.gmd.de/cats/projects
• Information about the project
• http//www.fokus.gmd.de/cats/publ
• Download this presentation
• Other CATS publications