\begin{slide}
	\Header{M. Tech Dissertation}
	\begin{center}
	{\LARGE Design and Evaluation of IEEE 802.11 based Dual MAC
	in MANETs}\\
	\end{center}
	\vspace{1.5cm}
	{Guides: \hfill \large Satyajit Rai}\\
	{\large Prof. Sridhar Iyer \hfill (\textit{01329009})}\\
	{\large Dr. Leena Chandran Wadia} \\
	\begin{center}\Red{\date} \end{center}
\end{slide}


\begin{slide}
\Header{Motivation}
	\begin{itemize} \large
	\item Traffic pattern in most of the Multihop Ad-Hoc Network
	applications is centralized.
	\item The nodes need to send data to one or more preferred
	destinations. For example,
		\begin{itemize}
		\item Military: Soldiers talk to commander.
		\item Disaster management teams: Stations talk to
		control/management center.
		\item Sensor Networks: Stations feed data to a central
		database.
		\end{itemize}
	\end{itemize}
\end{slide}

\begin{slide}
\Header{Hidden and Exposed Node Problems}
	\begin{center}
	\includegraphics[width=0.6\textwidth]{figures/hidden_exposed}
	\end{center}
	\begin{description}
	\item{\bf Hidden Node Problem: } If A and C want to transmit to B
	there will be collision at B, since A and C are hidden to each
	other.
	\item{\bf Exposed Node Problem: } If B is transmitting to A, C can
	not transmit to D, since it senses the medium busy.
	\end{description}
\end{slide}

\begin{slide}
\Header{Centralized Multihop Scenario}
	\begin{center}
	\includegraphics[width=0.7\textwidth]{figures/scenario}
	\end{center}

	\begin{itemize}
		\item The preferred destination is the \emph{central
			station}.
		\item Nodes within one-hop range of central station are
			\emph{inner stations}
		\item Stations at one hop distance are \emph{boundary
			stations}.
		\item Stations beyond one-hop are \emph{outer stations}.
	\end{itemize}
	\begin{overlay}{1}
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	\psline[linewidth=2pt,linecolor=blue]{<-}(0.3cm,0.3cm)(2cm,1.5cm)
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	}%
	\end{overlay}%
\end{slide}

\begin{slide}
\Header{Focus of the Work}
	\begin{itemize}\large
	\item We focus on performance of IEEE 802.11 MAC in centralized
	multihop ad hoc networks.
	\item Suggest design and architecture of a new MAC called Dual
	MAC for such a topology.
	\item Effect of station Mobility is not considered.
	\end{itemize}
\end{slide}

\begin{slide}
\Header{MAC in Multihop Networks}
	\begin{itemize} \large
	\item Multihop ad-hoc networks require a distributed medium access
	mechanism.
	\item We investigate IEEE 802.11 MAC as it is the most popular
	MAC for multihop ad-hoc networks.
	\item The Distributed Coordination Function (DCF) operation of
	IEEE 802.11 MAC provides the distributed medium access mechanism.
	\item The Point Coordination Function (PCF) operation of IEEE
	802.11 MAC provides a polled medium access mechanism, and is used
	in fixed Wireless LANs.
	\end{itemize}
\end{slide}

\begin{slide}
\Header{IEEE 802.11 DCF and PCF Operation}
\begin{center}
\includegraphics[height=0.50\textheight]{figures/dcf_working}\\
DCF Operation\\
\vspace{3mm}
\includegraphics[height=0.35\textheight]{figures/pcf_working}\\
PCF Operation
\end{center}
\end{slide}

\begin{slide}
\Header{Problems with Centralized Scenario}
	\begin{itemize}\large
	\item As the flows converge towards destination, nodes close to
	the preferred destination operate in high load condition.
	\item If the distributed MAC (DCF) is used, lot of stations try
	to access medium at the same time.
	\item This increases the collisions, and the throughput
	decreases heavily.
	\item It is well known that the scheduled MAC protocols perform
	better than distributed MAC protocols in high load conditions.
	\item We suggest using a scheduled MAC in one hop region around
	the central station.
	\end{itemize}
\end{slide}

\begin{slide}
\Header{Scheduled MAC in Multihop Networks}
	\begin{center} \includegraphics[height=0.5\textheight]{figures/hybrid}\end{center}
	\begin{itemize}\large
	\item Requirement for a scheduled MAC
	\begin{itemize}\normalsize
	\item The scheduled MAC must work smoothly with distributed MAC.
	\end{itemize}
	\item In an IEEE 802.11 Network, DCF is used as distributed MAC.
	\item PCF mode of 802.11 can serve as scheduled MAC.
	\end{itemize}
\end{slide}

\begin{slide}
\Header{Problems with PCF as scheduled MAC}
	\begin{itemize}\large
	\item During the Contention Free Period (CFP) of PCF, the NAV setting
	of stations around PC prevents them to communicate with
	outer stations.
	\item This means that these stations (esp. boundary stations)
	become exposed to PC during CFP.
	\item As there is not RTS/CTS exchange during CFP, the
	transmissions from outer stations could collide with the poll of
	the PC.
	\item This means that during the CFP, outer stations become
	hidden to PC, and vice versa.
	\end{itemize}
\end{slide}

\begin{slide}
\Header{Solution: Dual MAC}
\begin{center}
\includegraphics[height=0.6\textheight]{figures/dual_arch}
\end{center}
	\begin{itemize}\large
	\item We equip boundary stations with Dual MAC.
	\item Dual MAC is a MAC with two independent MACs
		\begin{itemize}\normalsize
		\item \emph{PCF MAC} communicates with PC in PCF mode,
		\item \emph{DCF MAC} communicates with outer stations in
		DCF mode.
		\end{itemize}
	\item However, the DCF MAC communication can still cause
	collisions with stations that are using PCF.
	\item To avoid this we use PCF on one channel and DCF on
	another.
	\item Dual MAC interface handles the data packets to/from
	appropriate MAC and channel.
	\end{itemize}
\end{slide}

\begin{slide}
\Header{Dual MAC: Working}
\scriptsize
\begin{Verbatim}[frame=single, commandchars=+\[\]]
+textit[For outgoing packets:]
        if ( packet is broadcast ) {
                send packet to both PCF MAC and DCF MAC;
        } else {
                channel = get_destination_MAC_channel(); 
                if ( channel == DCF_channel )
                        send packet on DCF MAC;
                else
                        send packet on PCF MAC;
        }

+textit[For incoming packets:]
        hand over the packet to Link Layer;
\end{Verbatim}
\end{slide}

\begin{slide}
\Header{Simulation and Results}
	\begin{itemize}\large
	\item We have implemented the Dual MAC in NS-2.
	\item Simulation was performed in NS with 50 stations spread
	around an area of 1500m x 1500m.
	\item Simulation setup
		\begin{itemize}\normalsize
		\item Central station (PC) at 750m x 750m.
		\item 8 stations use Dual MAC, and are 240m away from PC.
		\item 12 stations are inside one-hop boundary of PC, and
		use PCF.
		\item 29 stations are outside one hop boundary of PC, and
		use DCF.
		\item Routing protocol is DSDV.
		\end{itemize}
	\end{itemize}
\end{slide}

\begin{slide}
\Header{Results: Packet Delivery Ratio}
\begin{center}
\includegraphics[height=0.9\textheight]{figures/plot30}
\end{center}
\end{slide}

\begin{slide}
\Header{Results: Throughput}
\begin{center}
\includegraphics[height=0.9\textheight]{figures/thput}
\end{center}
\end{slide}

\begin{slide}
\Header{Conclusion and Future Work}
{\large Conclusion}
	\begin{itemize}
	\item Use of Dual MAC gives more throughput per channel than DCF,
	even with a small number of Dual Stations.
	\item The scheduled MAC can be used to increase throughput in a
	multihop ad-hoc networks.
	\item Dual MAC can act as interface between stations using
	scheduled and unscheduled MAC.
	\end{itemize}
{\large Future Work}
	\begin{itemize}
	\item A station could automatically switch-on PCF seeing high
	traffic in its surrounding.
	\item This would enable small groups of stations forming a
	cluster in high traffic areas, and use scheduled MAC to increase
	throughput.
	\end{itemize}
\end{slide}

\begin{slide}
\Header{Thank you}
\begin{center}
{\huge Thank You}
\end{center}
\end{slide}

