![](media/image1.jpeg){width="1.4791666666666667in"
height="0.4791666666666667in"} **Advanced Scientific Computing
Research**

**FY 2004 Accomplishment**

**Bandwidth Estimation: measurement methodologies and applications**

## Kimberly Claffy, CAIDA/SDSC/UCSD

Constantinos Dovrolis, Georgia Institute of Technology

Summary

***Internet resources are often used inefficiently due to the inability
of high bandwidth applications to accurately ascertain bandwidth
parameters in real-time. This SciDAC project strives to improve existing
bandwidth estimation techniques and tools, and to test and integrate the
most successful of these technologies into DOE and other network
infrastructures.***

More accurate and efficient bandwidth estimation tools and techniques
would enable high performance network engineering and management
functionality that have remained elusive for years, specifically the
capabilities to:

-   Automatically size TCP socket buffers to achieve better throughput.

-   Configure overlay routes for overlay networks.

-   Select the highest throughput server for content distribution.

-   Adjust the encoding rate on streaming applications.

-   Monitor path load to verify SLA and QoS targets.

-   Check for sufficient bandwidth as part of application admission
    control.

-   Construct application level topologies for peer-to-peer networks.

-   Select an egress ISP for interdomain traffic engineering.

Our specific progress towards meeting these needs includes:

**Survey of Current Tools:** "Bandwidth Estimation: Metrics, Measurement
Techniques, and Tools", published in *IEEE* *Network* magazine (Nov/Dec
2003), presents a taxonomy of currently available tools, comparing their
main differences and similarities.

**Refinement of Tool Testing methodology:** We improved our lab
environment and configuration and devised better methods for generating
realistic yet reproducible simulated cross-traffic. We also automated
test data collection and improved our capabilities for independently
measuring and graphing cross-traffic and tool traffic using a NeTraMet
passive monitor.

![](media/image2.png){width="2.9923611111111112in"
height="1.9791666666666667in"}

*Figure 1. Tool Traffic, Cross-traffic, and Passive Traffic Monitoring
in the Bandwidth Estimation Testbed. Tool traffic is shown between end
hosts in the upper part of this figure. Several options for generating
cross-traffic loads are illustrated in the lower part of the figure. All
three routers connect to the Spirent SmartBits 6000 at the center
bottom. A PC running the Spirent SmartFlow application controls the
direction, makeup, and load level of multiple logical traffic flows on
any or all physical links. Finally, a NeTraMet passive meter (top right)
runs a ruleset to track packet sizes and inter-arrival times from all
flows.*

**Analysis of E2E bandwidth estimation tools on both 100Mbps and
GigEther links:** Several factors affect tool accuracy including: the
presence of layer-2 store and forward devices; differences in the size
of internal router queues; and high cross-traffic loads. All of these
conditions are likely to occur in the Internet in the wild, complicating
the task of end-to-end bandwidth estimation.

**Testbed sharing with other DOE bandwidth estimation researchers:** We
opened up our bandwidth estimation test lab for use by DOE
collaborators.

**Application of Internet spectroscopy techniques to link capacity
characterization:** We began to investigate a new technique for
revealing characteristics of layer-2 technologies without requiring
additional traffic probes. Internet spectroscopy is based on an
algorithm where a radon transform of inter-packet delay distributions is
coupled with entropy minimization.

**Pathrate and Pathload in gigabit paths:**

New versions of our bandwidth estimation

tools, Pathrate and Pathload, were released

in January 2004. Pathrate v2.3.3 measures

end-to-end capacity (a.k.a., bottleneck

bandwidth), while Pathload v1.1.1 measures end-to-end available
bandwidth.

**Socket buffer sizing for maximum TCP throughput:** Bandwidth
estimation can significantly improve the throughput of large TCP
transfers, such as the transfers of large scientific data sets. We have
developed an application-layer technique, called *SOcket Buffer
Auto-Sizing (SOBAS)*, that helps TCP to achieve its maximum feasible
bandwidth in a network path. SOBAS does not require changes in TCP. The
key idea behind SOBAS is to limit the socket buffer size, and thus the
maximum TCP send-window, to the point that the transfer saturates the
network path without causing packet losses.

![](media/image3.wmf){width="3.0277777777777777in"
height="2.3472222222222223in"}

*Figure 2. TCP throughput is much higher when using SOBAS (upper graph).
SOBAS maintains the optimal socket buffer size at maximum lossless
receive throughput.*

**Plans:** This project ends in August 2004. We hope to leverage the
investment DOE has already made in improving the integrity of the
component technologies in a follow-on effort. To this end, we are
developing a proposal in collaboration with ORNL and the Pittsburgh
Supercomputer Center (PSC) for Pythia, an automatic performance
monitoring and problem diagnosis system for ultra high-speed networks.

**For further information on this subject contact:**

Dr. Margaret Murray, Program Manager

Cooperative Association for Internet Data Analysis (CAIDA) at the San
Diego Supercomputer Center

University of California, San Diego

Phone: (858) 534-8928 <margaret@caida.org>

Project URLs: <http://www.caida.org/projects/bwest/>

<http://www.pathrate.org/>