TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Cesar Marcondes, Anders Persson, M.Y. Sanadidi, Mario Gerla Computer Science Dept, UCLA, USA Rosario Firrincieli DEIS/ARCES, University of Bologna, Italy David R. Beering, Greg Romaniak Infinite Global Infrastructures, LLC, USA Tridentcom 2006, Barcelona, Spain

Outline

      Rationale Overview Methodology Testbed description Examples of results – – satellite channel characterization impact of satellite errors on TCP – Performance Enhancing Proxies Conclusions

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli

Rationale

 TCP NewReno does not perform efficiently in large BDP environments  Many studies address TCP in large BDP networks focusing mainly on high capacity networks  It is necessary to study also high-delay environments such as mixed satellite networks  However, satellite resources are very scarce and most satellite TCP optimization rely only on simulation and emulation tools

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli

Overview

 Over the period of a month, a measurement campaign on a real satellite environment has been conducted  The goal was to determine TCP performance varying the channel conditions (non-congestion errors, cross-traffic)  Moreover, state-of-the-art Performance Enhancing Proxies (PEP) have been tested  Not only do we present our results, but we also describe the complex testbed deployment, methodology and the lessons that we learned

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli

Methodology

   Limitation of experimental measures: – satellite services must be suspended during measures – availability of only few hours Simulations allow a highly planned experiment outline selecting a limited number of scenarios to be tested Measures are compared with simulation results – differences are investigated by means of emulations ns-2 simulations FreeBSD emulations IGI system experimental measures

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli

Testbed topology

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli

Sat channel characterization (1)

   GEO satellite link are usually very robust thanks to their physical layer codes. Link errors are very common when mobility and extreme weather conditions are involved We forced errors on the satellite link by means of power adjustments on the modulators/demodulators A constant rate stream of packets was used (UDP traffic) Low error rate = 0.53% Extremely high error rate = 92%

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli

Sat channel characterization (2)

  Packets are dropped in bulks showing a behavior similar to the 2-state Gilbert-Elliot channel model Real measures gave us the guideline to reproduce this behavior in the simulator Average packet error rate = 0.1% Measures drive simulations!

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli

Impact of satellite errors on TCP

   TCP NewReno does not distinguish between congestion and link errors As a consequence the congestion window is halved many times due to link errors TCP Westwood is an example of TCP modification that distinguishes between congestion and link errors Measures are close to simulations!

Error level experienced across experiments TCP performance under errors

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli

Cross traffic effects

 The effects of a UDP spike traffic on TCP Westwood have been evaluated Simulation Emulation Simulations drive emulations!

Emulation with fix

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli

PEP: description (1)

 Based on the introduction of an intermediate agent (proxy) which alters the end-to-end semantics of TCP  Tested PEPs implement a splitting approach and belong to the category of transport layer PEP [RFC 3135] TCP server (sender side) Application TCP IP internet PEP agent (uplink gateway) TCP IP PEP TCP IP PEP agent (downlink gateway) PEP TCP IP TCP IP internet TCP client (receiver side) Application TCP IP

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli

PEP: description (2)

Name Description TCP variants on satellite link Flow control technique Error recovery technique Fast Start (RFC 1644 -T/TCP) Data compression Data prefetch Mentat SkyX

Commercial box based on Linux XTP, SCPS-TS Rate based Window based SNACK Yes Yes Yes

ViaSat iPEP

Commercial box based on Linux and Solaris TCP-XL

SaTPEP

Public module for ns-2 simulator SatPEP Window based Rate based ECN Yes No No NACK No No No

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli

PEP: results (1)

 Three connections start with 30 s of delay each other – Adaptability SaTPEP

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli

SaTPEP

PEP: results (2)

SaTPEP Mentat SkyX

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli

SaTPEP

PEP: results (3)

Measures are far from simulations!

Mentat SkyX Viasat iPEP Mentat SkyX

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli

Conclusions

   We had an opportunity to perform extensive tests on a mixed network composed by a real GEO satellite and high-speed Internet Main contributions: – – – sharing our experiences on running an iterative simulation/measures/emulation methodology satellite channel errors characterization analysis of TCP Westwood on a real satellite channel – studying/debugging of two PEP boxes (Mentat SkyX, Viasat iPEP) Open issues: – – further optimization of TCP on satellite channel evaluation of new architectures for mixed Internet and GEO satellite environment

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli

Thanks!

Rosario Firrincieli PhD Student DEIS/ARCES University of Bologna [email protected]

http://www.arces.unibo.it

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results

Rosario Firrincieli