RFC 2041 (rfc2041) - Page 2 of 27

Mobile Network Tracing

RFC 2041                 Mobile Network Tracing             October 1996


1. Introduction

   How does one accurately capture and reproduce the observed behavior
   of a network?  This is an especially challenging problem in mobile
   computing because the network quality experienced by a mobile host
   can vary dramatically over time and space.  Neither long-term average
   measures nor simple analytical models can capture the variations in
   bandwidth, latency, and signal degradation observed by such a host.
   In this RFC, we describe a solution based on network tracing.  Our
   solution consists of two phases:  trace recording and trace
   modulation.

   In the trace recording phase, an experimenter with an instrumented
   mobile host physically traverses a path of interest to him.  During
   the traversal, packets from a known workload are generated from a
   static host.  The mobile host records observations of both packets
   received from the known workload as well as the device
   characteristics during the workload.  At the end of the traversal,
   the list of observations represents an accurate trace of the observed
   network behavior for this traversal.  By performing multiple
   traversals of the same path, and by using different workloads, one
   can obtain a trace family that collectively characterizes network
   quality on that path.

   In the trace modulation phase, mobile system and application software
   is subjected to the network behavior observed in a recorded trace.
   The mobile software is run on a LAN-attached host whose kernel is
   modified to read a file containing the trace (possibly postprocessed
   for efficiency,) and to delay, drop or otherwise degrade packets in
   accordance with the behavior described by the trace.  The mobile
   software thus experiences network quality indistinguishable from that
   recorded in the trace.  It is important to note that trace modulation
   is fully transparent to mobile software --- no source or binary
   changes have to be made.

   Trace-based approaches have proved to be of great value in areas such
   as file system design [2, 10, 11] and computer architecture.  [1, 5,
   13] Similarly, we anticipate that network tracing will prove valuable
   in many aspects of mobile system design and implementation.  For
   example, detailed analyses of traces can provide insights into the
   behavior of mobile networks and validate predictive models.  As
   another example, it can play an important role in stress testing and
   debugging by providing the opportunity to reproduce the network
   conditions under which a bug was originally uncovered.  As a third
   example, it enables a system under development to be subjected to
   network conditions observed in distant real-life environments.  As a
   final example, a set of traces can be used as a benchmark family for
   evaluating and comparing the adaptive capabilities of alternative



Noble, et. al.               Informational