sigcomm 2008 2008 andreas haeberlen, mpi-sws 1 satellitelab: adding heterogeneity to...

© 2008 Andreas Haeberlen, MPI-SWS 1SIGCOMM 2008

SatelliteLab: Adding Heterogeneity to Planetary-Scale Network Testbeds

Andreas Haeberlen

MPI-SWS / Rice University

Marcel Dischinger MPI-SWS

Ivan Beschastnikh University of Washington

Krishna P. Gummadi

MPI-SWS

Stefan Saroiu University of Toronto

2© 2008 Andreas Haeberlen, MPI-SWS SIGCOMM 2008

Why are testbeds so popular?

Testbeds provide wide-area network paths Realistic network paths are crucial for evaluating

the performance of distributed systems

Your clusterTestbeds

PLANETLAB

vs.


Access networks and heterogeneity

Internet bottlenecks are in access networks Studies show that most queueing, loss etc. happens there

Access networks have high heterogeneity Cable, DSL, GPRS, UMTS, EVDO, 802.11, Satellite, Dial-up...

Not represented in existing testbeds

Internet BackboneAccess

networks


Growing the testbed is not enough

Can we simply add more nodes? More nodes from acad. networks do not improve heterogeneity Nodes from the commercial Internet are much more effective

Need nodes from the commercial Internet

280 PlanetLab nodesin U.S. and Europe

27 end nodesin U.S. and Europe

Inte

r-AS

links

cov

ered

Node index


Challenges1) Make it easy for volunteers to contribute

Will not allow arbitrary code to run on their machines Do not want to spend time managing software Do not want to deal with complaints

2) Keep testbed easy to use for experimenters Resources may vary widely (cell phone vs. workstation) Nodes may have different OSes, hardware, software... Nodes may be behind middleboxes (NATs, firewalls, ...)


A new testbed architecture

Idea: Separate computation and communication Tier 1: Powerful, well-connected nodes (from existing testbed)

Contribute computation power, memory, storage... Tier 2: Light-weight nodes

Contribute "just their access-network links"

Tier 1

Tier 2

"Planets"

"Satellites"


Outline Motivation SatelliteLab Evaluation Applications Conclusion


Delegation

Delegate code execution to the planets Problem: Changes the network path Misses the access links

Solution: Send traffic through the satellites

Planet A Planet B

Satellite A Satellite B

Application

Network path

Network path

Adds somelatency


Detour routing

Two challenges remain: Satellites are sending traffic that may trigger complaints NATs and firewalls may prevent connectivity

Solution: Detour traffic through the planets

Planet A Planet B


Firewall


The SatelliteLab detour path

To send a packet from planet A to planet B:1. A intercepts the data packet2. A exchanges a probe packet with its satellite3. A sends the data packet to B4. B exchanges a probe packet with its satellite5. B delivers the data packet

Planet A Planet B


Actual path

"Ideal" path


Challenges revisited1) Make it easy for volunteers to contribute

No complaints: Satellites only communicate with their planet

No hassle: Sufficient to install the satellite helper once No CPU slowdown: Planets do all the heavy lifting No security risk: Satellite is just 118 lines of Java code

2) Keep testbed easy to use for experimenters All application code runs on the planets No need to deal with middleboxes No resource limitations due to satellites Works with unmodified binaries


Outline Motivation SatelliteLab Evaluation Applications Conclusion


Evaluation Is it feasible to recruit edge nodes? Is the availability sufficient for

experiments? Can satellites find a nearby planet? Does SatelliteLab preserve...

the path capacity? the queueing delay? the jitter? the packet loss rates?

Yes.Yes.

Yes.

Yes.Yes.

Yes.Yes.


Is it feasible to recruit edge nodes?

Built a prototype testbed Asked friends and family to install satellite software

Increased heterogeneity with very little effort Ten U.S. states, six countries, 15 commercial ISPs Technologies: Cable, DSL, Ethernet, Wi-Fi, ISDN, BT, EVDO

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DSL+Wi-FiEVDOCable+Wi-FiCableDSLCable+Wi-FiUniCable+Wi-FiDSL+Wi-FiCable+Wi-FiCable+Wi-FiCableCableCable+Wi-FiCable+Wi-FiDSL

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# Location Access link NAT Type Mob. # Location Access link NAT Type Mob.


SatelliteLab preserves path capacity

Direct path vs. interplanetary path Large difference because bottlenecks are in access networks

Detour routing preserves the path capacity

Direct path

SatelliteLab pathPA PB

SA SB

Interplanetary path


SatelliteLab preserves queueing delay

Same comparison for queueing delay Almost all the queueing is in the access networks

Detour routing preserves the queueing delay

Interplanetary pathPA PB

SA SBDirect path

SatelliteLab path


Outline Motivation SatelliteLab Evaluation Applications

Network coordinate system Overlay multicast TCP throughput over cellular links

Conclusion


Application: Network coordinates

Need to measure RTT between nodes Surprising observation (in previous work):

Discarding outliers improves network coordinates on PlanetLab [NSDI'06] but not when deployed with Azureus BitTorrent client [NSDI'07]

Reason: Huge RTT variance PlanetLab did not predict this observation Could SatelliteLab have predicted it?

Figures taken from [NSDI'07]


Application: Network coordinates We ran an experiment with several Azureus

nodes on SatelliteLab We observed same effect as in [NSDI'07]

SatelliteLab could have predicted this outcome!

Can we also use SatelliteLab to explain it? Yes - Measurements revealed extremely long queues on

the broadband access links Azureus downloads fill up the queues high RTT variance!


Summary Existing testbeds lack heterogeneity SatelliteLab: A new testbed architecture

for heterogeneous testbeds Introduces satellites, a new class of light-weight nodes Enables experimenters to improve heterogenity by

recruiting end nodes as satellites Builds on existing testbeds and preserves many of their

useful properties: Ease of use, ease of management...


SatelliteLab is for YOU! We have a new testbed

that you can use for your experiments

To run an experiment, you need: some planets (e.g., nodes from PlanetLab) some satellites (e.g., nodes from friends or

colleagues) the SatelliteLab software

http://satellitelab.mpi-sws.org/

sigcomm 2008 2008 andreas haeberlen, mpi-sws 1 satellitelab: adding heterogeneity to...

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