RFC 2041 (rfc2041) - Page 3 of 27

Mobile Network Tracing

RFC 2041                 Mobile Network Tracing             October 1996


   mobile system designs.

   Our goal in writing this RFC is to encourage the development of a
   widely-accepted standard format for network traces.  Such
   standardization will allow traces to be easily shared.  It will also
   foster the development and widespread use of trace-based benchmarks.
   While wireless mobile networks are the primary motivation for this
   work, we have made every effort to ensure that our work is applicable
   to other types of networks.  For example, the trace format and some
   of the tools may be valuable in analyzing and modeling ATM networks.

   The rest of this RFC is organized as follows.  We begin by examining
   the properties of wireless networks and substantiating the claim that
   it is difficult to model such networks.  Next, in Section 3, we
   describe the factors that should be taken into account in designing a
   trace format.  We present the details of a proposed trace format
   standard in Section 4.  Section 5 presents a set of tools that we
   have built for the collection, analysis and replay of traces.
   Finally, we conclude with a discussion of related and future work.

2. Modeling Wireless Networks

   Wireless channels are particularly complex to model, because of their
   inherent dependence on the physical properties of radio waves (such
   as reflections from "hard" surfaces, diffraction around corners, and
   scattering caused by small objects) and the site specific geometries
   in which the channel is formed.  They are usually modeled as a time-
   and distance-varying signal strength, capturing the statistical
   nature of the interaction among reflected radio waves.  The signal
   strength can vary by several orders of magnitude (+ or - 20-30 dB)
   within a short distance.  While there have been many efforts to
   obtain general models of radio propagation inside buildings and over
   the wide area, these efforts have yielded inherently inaccurate
   models that can vary from actual measurements by an order of
   magnitude or more.

   Signal-to-noise ratio, or SNR, is a measure of the received signal
   quality.  If the SNR is too low, the received signal will not be
   detected at the receiver, yielding bit errors and packet losses.  But
   SNR is not the only effect that can lead to losses.  Another is
   inter-symbol interference caused by delay spread, that is, the
   delayed arrival of an earlier transmitted symbol that took a
   circuitous propagation path to arrive at the receiver, thereby
   (partially) canceling out the current symbol.  Yet another problem is
   doppler shift, which causes frequency shifts in the arrived signal
   due to relative velocities of the transmitter and the receiver,
   thereby complicating the successful reception of the signal.  If
   coherent reception is being used, receiver synchronization can be



Noble, et. al.               Informational