in an interpreted language, presently Tcl, providing considerable
flexibility. However, there is no mechanism to synthesize such
scripts -- they must be explicitly designed. Furthermore, the use of
an interpreted language such as Tcl limits the use of PFI to user-
level implementations of network drivers, and may have performance
implications.
7. Future Work
This work is very much in its infancy; we have only begun to explore
the possible uses for mobile network traces. We have uncovered
several areas of further work.
The trace format as it stands is very IP-centric. While one could
imagine using unknown IP addresses for non-IP hosts, while using
header-only properties to encode other addressing schemes, this is
cumbersome at best. We are looking into ways to more conveniently
encode other addressing schemes, but are content to focus on IP
networks for the moment.
Two obvious questions concerning wireless media are the following.
How does a group of machines perform when sharing the same bandwidth?
How asymmetric is the performance of real-world wireless channels?
While we do have tools for merging traces taken from multiple hosts
into a single trace file, we've not yet begun to examine such
multiple-host scenarios in depth. We are also looking into
instrumenting wireless base stations as well as end-point hosts.
Much of our planned work involves the PaM testbed. First and
foremost, many wireless channels are known to be asymmetric;
splitting the replay trace into incoming and outgoing modulation
entries is of paramount importance. We would like to extend PaM to
handle multiple emulated interfaces as well as applying different
modulation parameters to packets from or to different destinations.
One could also imagine tracing performance from several different
networking environments, and switching between such environments
under application control. For example, consider a set of traces
showing radio performance at various altitudes; an airplane simulator
in a dive would switch from high-altitude modulation traces to low-
altitude ones.
Finally, we are anxious to begin exploring the properties of real-
world mobile networks, and subjecting our own mobile system designs
to PaM to see how they perform. We hope others can make use of our
tools to do the same.
Acknowledgements
The authors wish to thank Dave Johnson, who provided early pointers
to related work and helped us immeasurably in RFCformatting. We
also wish to thank those who offered comments on early drafts of the
document: Mike Davis, Barbara Denny, Mark Lewis, and Hui Zhang.
Finally, we would like to thank Bruce Maggs and Chris Hobbs, our
first customers!
This research was supported by the Air Force Materiel Command (AFMC)
and ARPA under contract numbers F196828-93-C-0193 and DAAB07-95-C-
D154, and the State of California MICRO Program. Additional support
was provided by AT&T, Hughes Aircraft, IBM Corp., Intel Corp., and
Metricom. The views and conclusions contained here are those of the
authors and should not be interpreted as necessarily representing the
official policies or endorsements, either express or implied, of
AFMC, ARPA, AT&T, Hughes, IBM, Intel, Metricom, Carnegie Mellon
University, the University of California, the State of California, or
the U.S. Government.
Security Considerations
This RFCraises no security considerations.
Authors' Addresses
Questions about this document can be directed to the authors:
Brian D. Noble
Computer Science Department
Carnegie Mellon University
5000 Forbes Avenue
Pittsburgh, PA 15213-3891
Phone: +1-412-268-7399
Fax: +1-412-268-5576
EMail: bnoble@cs.cmu.edu
Giao T. Nguyen
Room 473 Soda Hall #1776 (Research Office)
University of California, Berkeley
Berkeley, CA 94720-1776
Phone: +1-510-642-8919
Fax: +1-510-642-5775
EMail: gnguyen@cs.berkeley.edu
Mahadev Satyanarayanan
Computer Science Department
Carnegie Mellon University
5000 Forbes Avenue
Pittsburgh, PA 15213-3891
Phone: +1-412-268-3743
Fax: +1-412-268-5576
EMail: satya@cs.cmu.edu
Randy H. Katz
Room 231 Soda Hall #1770 (Administrative Office)
University of California, Berkeley
Berkeley, CA 94720-1770
Phone: +1-510-642-0253
Fax: +1-510-642-2845
EMail: randy@cs.berkeley.edu
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