% $Id: methodology.tex,v 1.7 2005/03/01 08:06:33 gokhale Exp $

\section{Evaluation Methodology}
\label{sec:eval}

For studying the relationships of infrastructure and application
properties of sensor networks, we used an evaluation environment
within the NS-2~\cite{NS-2} discrete event simulator. The underlying
MAC layer was IEEE 802.11, the physical radio characteristics of each
node's network interface, such as transmit power, receiver
sensitivity, data load and antenna type were chosen so as to
approximate the Lucent WaveLan direct sequence spread spectrum
radio. The evaluations were based on the simulation of sensor nodes
which were distributed and moving within a
%Andy: we dont have biased topology now, so we can remove (either biased
%or uniform)
% OK, removed - but we can think about this for the next paper.
square flat space of 1000m X 1000m for 100 seconds of simulation
time. The mobility model used was the random waypoint
model~\cite{Johnson_RWP:96,Bettstetter:03}.
% Andy: This index is not correct, here is the reference I used, this
%is not present in the references:
% Ok, I used both - Andy

The network parameters of interest to us was the sensor network
size. This parameter were varied for the different protocols described
in Section~\ref{sec:overview}. Increasing the total nodes in a network
will not necessarily increase the network performance, for the same
topology since denser node will have more collisions, possibly node
failures and hence congestion. The simulations are run for 100, 196,
289 and 400 nodes for the same square flat space described
above~\cite{Tilak:02}.   
%Andy: Tilak et al reference at the end of above line
% DONE
\iffalse
\item {\bf Node deployment:} this indicates how nodes are distributed,
      such as whether they are biased towards the source nodes
      (assuming that source nodes are stationary) or whether the
      deployment is uniform.  
\fi


%Andy: Node deployment should be commented as this is not there in the
%doc I have sent you.
% DONE
The data-dissemination protocols mainly address the observer mobility
issue. As such it is critical to study the behavior of protocols
varying the following parameters:
\begin{enumerate}\cramplist  
\item {\bf number of observers ({\em i.e.}, sinks nodes):} Network
      performance against increasing sink nodes is an important metric
      since it is indicative of how well the network scales as sink
      nodes. We call the total number of sink nodes in the simulation
      as sink size. 
\iffalse
% commented out - why did we comment this out
%Andy, we have not discussed the results with increasing sink speeds
%since they dont change the results much. Instead, I have mentioned
%pause time since that is also a measure of node mobility.
\item sink speeds: Increased sink movements leads to more frequent
      changes in dissemination path (and potentially increased
      traffic), thus it is interesting to observe protocol efficiency
      for increased sink speeds.  
\fi
\item {\bf pause time:} In the sensor network, each node remains
      initially stationary for a fixed period of time, known as the
      pause time. A destination is then selected from the flat
      simulation space defined and then a node starts moving towards
      the destination. The speed of the node varies from 0 to some
      maximum speed specified at the beginning of simulation. On
      reaching the destination, the node again pauses for the fixed
      time, at the end of which it selects another destination and the
      process is repeated for simulation time. Pause time is thus a
      measure of sink mobility, since lower pause time indicates
      highly mobile sinks, while longer pause times mean the sinks are
      stationary for longer periods. Increased sink movements leads to
      more frequent changes in dissemination path (and potentially
      increased traffic). Thus it is interesting to observe  protocol
      efficiency for increased sink mobility. Such an experimental
      setup was important in order to challenge the protocols in an
      environment where they would be most applicable. 
\end{enumerate}

The simulations are run for reports generated (by source nodes) every
0.25 seconds. In order to have a direct comparison for the protocols
being studied, the same environment variables with identical loads
were used for the all experiments. The same movement files, which
describe the movement of nodes in the sensor network are used for both
the protocols. The simulations were run with movement patterns which
were generated for seven different pause times including 1, 2, 10, 25,
40, 50 and 75 seconds. Eight different values for the number
of sink nodes were used including 2, 4, 6, 8, 10, 12, 14 and 16 sinks
nodes. 

\iffalse
% Not required.
 as shown in Table~\ref{tbl:exp}.

\begin{table}[htb]
\begin{center}
\bfcaption{Experimental Setup}
\begin{tabular}{||r|r|r||}\hline
\multicolumn{1}{||c|}{\bf Sensor nodes} & \multicolumn{1}{|c|}{\bf
Sink nodes}	& \multicolumn{1}{|c|}{\bf Pause} \\ \hline 
100	& 2	& 1 \\
196	& 4	& 2 \\
289	& 6 & 10 \\
400	& 8 & 25  \\ 
    & 10 & 40 \\
    & 12 & 50 \\
    & 14 & 75 \\
    & 16 &    \\ \hline \hline
\end{tabular}
\label{tbl:exp}
\end{center}
\end{table}
\fi

