Transcript TCP/IP Over LEO Satellites - of Marc Emmelmann (www

Competence Center for
Advanced Network Technologies and Systems
TCP/IP Over LEO Satellites
Related Activities within the ATM-Sat
Project
Presentation to Industry Representatives and
Interested Scientists
http://www.fokus.gmd.de
http://www.fokus.gmd.de/cats
Marc Emmelmann
Contents

Test- & Measurement Suite




Global Set-Up
Probe Station
Simulation Environment
First Simulation Results
2000-12-12
Marc Emmelmann
2
Global Set-Up
Satellite
Channel
Emulation
Probe Station
Satellite
Satellite
Modem
Modem
ATM-Sat Demonstrator Hardware
2000-12-12
Probe Station
Marc Emmelmann
3
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
2000-12-12
Marc Emmelmann
4
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, ...
2000-12-12
Marc Emmelmann
5
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, ...
2000-12-12
Marc Emmelmann
6
Where We Are ...


Test- & Measurement Suite 
Simulation Environment



General Aspects
System Parameter
First Simulation Results
2000-12-12
Marc Emmelmann
7
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
2000-12-12
Marc Emmelmann
8
System Parameters






Satellite Orbit
Bit Rates
Bit Error Rate
Up- & Down-Link Delay
Intra-Satellite Delay
End-to-End Delay
2000-12-12
Marc Emmelmann
9
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%
2000-12-12
Marc Emmelmann
10
Bit Rates
ISL: 7 - 10 Gbit/s
Service Uplink (fixed):
2.048 Mbit/s
Feeder Up & Downlink:
32.768 Mbit/s
Service Uplink (portable):
384 kbit/s
Service Downlink:
32.768 Mbit/s
2000-12-12
Marc Emmelmann
11
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
2000-12-12
Marc Emmelmann
12
Up- & Down-Link Delay


Based upon analytically gained distance
Comparison analytical vs. simulated delay
2000-12-12
Marc Emmelmann
13
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
2000-12-12
Marc Emmelmann
14
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
2000-12-12
Marc Emmelmann
15
Where We Are ...



Test- & Measurement Suite 
Simulation Environment 
First Simulation Results




Link Model Description
Link Model Verification
RTT Measurement of TCP
Future Steps
2000-12-12
Marc Emmelmann
16
Link Model Description

Link:




Delay



Point-to-point
Symmetrical or asymmetrical
Wired
Function of time
Deterministic, periodical
Configurable Parameter:


BER
Bit rate
2000-12-12
Marc Emmelmann
17
Link Model Verification

Delay:



Expected values
Consider queuing delay
Bit rate

Upper Limit
2000-12-12
Marc Emmelmann
18
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 delay
variation
2000-12-12
Marc Emmelmann
19
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
2000-12-12
Marc Emmelmann
20
World Wide Web

http://www.fokus.gmd.de


http://www.fokus.gmd.de/cats


Information about the Competence Center CATS
http://www.fokus.gmd.de/cats/projects


Information about FOKUS
Information about the project
http://www.fokus.gmd.de/cats/publ


Download this presentation
Other CATS publications
2000-12-12
Marc Emmelmann
21