Competence Center forAdvanced Network Technologies and Systems

http://www.fokus.gmd.de/catshttp://www.fokus.gmd.de

Marc Emmelmann

TCP/IP Over LEO Satellites

Related Activities within the ATM-Sat Project

Presentation to Industry Representatives and Interested Scientists

2000-12-12 Marc Emmelmann 2

Contents

Test- & Measurement Suite Global Set-Up Probe Station

Simulation Environment First Simulation Results

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Global Set-Up

Probe Station

Satellite

Channel

Emulation

Satellite

Modem

Satellite

Modem

Probe StationATM-Sat Demonstrator Hardware

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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

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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, ...

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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, ...

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Where We Are ...

Test- & Measurement Suite Simulation Environment

General Aspects System Parameter

First Simulation Results

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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

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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

Feeder Up & Downlink:32.768 Mbit/s

ISL: 7 - 10 Gbit/s

Service Downlink:32.768 Mbit/s

Service Uplink (fixed):2.048 Mbit/s

Service Uplink (portable):384 kbit/s

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Bit Error Rate

BER at target system above MAC Up- & Down-Link

Good weather condition: 2*10E-8 Rain

causes link to collaps last for approx. 10 minutes

“on-off” modell ISLs Limitations

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Up- & Down-Link Delay

Based upon analytically gained distance Comparison analytical vs. simulated delay

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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

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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

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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 closer

to real round-trip delayvariation

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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

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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