tcp in mixed internet and geo-satellite environments: experiences and results

Tridentcom 2006, Barcelona, SpainTridentcom 2006, Barcelona, Spain

TCP in Mixed Internet and GEO-TCP in Mixed Internet and GEO-

SatelliteSatellite

Environments: Experiences and Environments: Experiences and

ResultsResultsCesar 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

OutlineOutline

Rationale

Overview

Methodology

Testbed description

Examples of results

– satellite channel characterization

– impact of satellite errors on TCP

– Performance Enhancing Proxies

Conclusions


Rosario Firrincieli

RationaleRationale

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


Rosario Firrincieli

OverviewOverview

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


Rosario Firrincieli

MethodologyMethodology

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-2simulations

IGI systemexperimental

measures

FreeBSDemulations


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Testbed topologyTestbed topology


Rosario Firrincieli

Sat channel characterization Sat channel characterization (1)(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%


Rosario Firrincieli

Sat channel characterization Sat channel characterization (2)(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!


Rosario Firrincieli

Impact of satellite errors on Impact of satellite errors on TCP 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!


Rosario Firrincieli

Cross traffic effectsCross traffic effects

The effects of a UDP spike traffic on TCP Westwood have been evaluated

Simulation Emulation

Emulation with fix

Simulations drive emulations!


Rosario Firrincieli

PEP: description (1)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


Rosario Firrincieli

PEP: description (2)PEP: description (2)

Name Mentat SkyX ViaSat iPEP SaTPEP

Description Commercial box based on Linux

Commercial box based on Linux and

Solaris

Public module for ns-2 simulator

TCP variants on satellite link XTP, SCPS-TS TCP-XL SatPEP

Flow control technique Rate based

Window based

Window based Rate based

Error recovery technique SNACK ECN NACK

Fast Start (RFC 1644 -T/TCP)

Yes Yes No

Data compression Yes No No

Data prefetch Yes No No


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PEP: results (1) PEP: results (1)

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

SaTPEP


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SaTPEP

PEP: results (2)PEP: results (2)

Mentat SkyX

SaTPEP


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PEP: results (3)PEP: results (3)

Mentat SkyX

SaTPEP

Mentat SkyX

Viasat iPEP

Measures are far from simulations!


Rosario Firrincieli

ConclusionsConclusions

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


Rosario Firrincieli

Thanks!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

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