Tridentcom 2006, Barcelona, Spain 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

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results Rosario Firrincieli 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 IGI system experimental measures FreeBSD emulations

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) Extremely high error rate = 92% Low error rate = 0.53%

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 Error level experienced across experiments TCP performance under errors Measures are close to simulations!

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 Emulation with fix Simulations drive emulations!

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] IP TCP Application IP TCP Application TCP server (sender side) TCP client (receiver side) PEP agent (uplink gateway) internet PEP agent (downlink gateway) internet IP TCP IP PEP TCP IP PEP TCP IP TCP

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results Rosario Firrincieli PEP: description (2) NameMentat SkyXViaSat iPEPSaTPEP DescriptionCommercial box based on Linux Commercial box based on Linux and Solaris Public module for ns-2 simulator TCP variants on satellite link XTP, SCPS-TSTCP-XLSatPEP Flow control technique Rate based Window based Rate based Error recovery techniqueSNACKECNNACK Fast Start (RFC T/TCP) Yes No Data compressionYesNo Data prefetchYesNo

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) Mentat SkyX SaTPEP

TCP in Mixed Internet and GEO-Satellite Environments: Experiences and Results Rosario Firrincieli PEP: results (3) Mentat SkyX SaTPEP Mentat SkyX Viasat iPEP Measures are far from simulations!

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! PhD Student DEIS/ARCES University of Bologna