\documentclass[11pt,twoside]{article}\makeatletter

\IfFileExists{xcolor.sty}%
  {\RequirePackage{xcolor}}%
  {\RequirePackage{color}}
\usepackage{colortbl}
\usepackage{wrapfig}
\usepackage{ifxetex}
\ifxetex
  \usepackage{fontspec}
  \usepackage{xunicode}
  \catcode`⃥=\active \def⃥{\textbackslash}
  \catcode`❴=\active \def❴{\{}
  \catcode`❵=\active \def❵{\}}
  \def\textJapanese{\fontspec{Noto Sans CJK JP}}
  \def\textChinese{\fontspec{Noto Sans CJK SC}}
  \def\textKorean{\fontspec{Noto Sans CJK KR}}
  \setmonofont{DejaVu Sans Mono}
  
\else
  \IfFileExists{utf8x.def}%
   {\usepackage[utf8x]{inputenc}
      \PrerenderUnicode{–}
    }%
   {\usepackage[utf8]{inputenc}}
  \usepackage[english]{babel}
  \usepackage[T1]{fontenc}
  \usepackage{float}
  \usepackage[]{ucs}
  \uc@dclc{8421}{default}{\textbackslash }
  \uc@dclc{10100}{default}{\{}
  \uc@dclc{10101}{default}{\}}
  \uc@dclc{8491}{default}{\AA{}}
  \uc@dclc{8239}{default}{\,}
  \uc@dclc{20154}{default}{ }
  \uc@dclc{10148}{default}{>}
  \def\textschwa{\rotatebox{-90}{e}}
  \def\textJapanese{}
  \def\textChinese{}
  \IfFileExists{tipa.sty}{\usepackage{tipa}}{}
\fi
\def\exampleFont{\ttfamily\small}
\DeclareTextSymbol{\textpi}{OML}{25}
\usepackage{relsize}
\RequirePackage{array}
\def\@testpach{\@chclass
 \ifnum \@lastchclass=6 \@ne \@chnum \@ne \else
  \ifnum \@lastchclass=7 5 \else
   \ifnum \@lastchclass=8 \tw@ \else
    \ifnum \@lastchclass=9 \thr@@
   \else \z@
   \ifnum \@lastchclass = 10 \else
   \edef\@nextchar{\expandafter\string\@nextchar}%
   \@chnum
   \if \@nextchar c\z@ \else
    \if \@nextchar l\@ne \else
     \if \@nextchar r\tw@ \else
   \z@ \@chclass
   \if\@nextchar |\@ne \else
    \if \@nextchar !6 \else
     \if \@nextchar @7 \else
      \if \@nextchar (8 \else
       \if \@nextchar )9 \else
  10
  \@chnum
  \if \@nextchar m\thr@@\else
   \if \@nextchar p4 \else
    \if \@nextchar b5 \else
   \z@ \@chclass \z@ \@preamerr \z@ \fi \fi \fi \fi
   \fi \fi  \fi  \fi  \fi  \fi  \fi \fi \fi \fi \fi \fi}
\gdef\arraybackslash{\let\\=\@arraycr}
\def\@textsubscript#1{{\m@th\ensuremath{_{\mbox{\fontsize\sf@size\z@#1}}}}}
\def\Panel#1#2#3#4{\multicolumn{#3}{){\columncolor{#2}}#4}{#1}}
\def\abbr{}
\def\corr{}
\def\expan{}
\def\gap{}
\def\orig{}
\def\reg{}
\def\ref{}
\def\sic{}
\def\persName{}\def\name{}
\def\placeName{}
\def\orgName{}
\def\textcal#1{{\fontspec{Lucida Calligraphy}#1}}
\def\textgothic#1{{\fontspec{Lucida Blackletter}#1}}
\def\textlarge#1{{\large #1}}
\def\textoverbar#1{\ensuremath{\overline{#1}}}
\def\textquoted#1{‘#1’}
\def\textsmall#1{{\small #1}}
\def\textsubscript#1{\@textsubscript{\selectfont#1}}
\def\textxi{\ensuremath{\xi}}
\def\titlem{\itshape}
\newenvironment{biblfree}{}{\ifvmode\par\fi }
\newenvironment{bibl}{}{}
\newenvironment{byline}{\vskip6pt\itshape\fontsize{16pt}{18pt}\selectfont}{\par }
\newenvironment{citbibl}{}{\ifvmode\par\fi }
\newenvironment{docAuthor}{\ifvmode\vskip4pt\fontsize{16pt}{18pt}\selectfont\fi\itshape}{\ifvmode\par\fi }
\newenvironment{docDate}{}{\ifvmode\par\fi }
\newenvironment{docImprint}{\vskip 6pt}{\ifvmode\par\fi }
\newenvironment{docTitle}{\vskip6pt\bfseries\fontsize{22pt}{25pt}\selectfont}{\par }
\newenvironment{msHead}{\vskip 6pt}{\par}
\newenvironment{msItem}{\vskip 6pt}{\par}
\newenvironment{rubric}{}{}
\newenvironment{titlePart}{}{\par }

\newcolumntype{L}[1]{){\raggedright\arraybackslash}p{#1}}
\newcolumntype{C}[1]{){\centering\arraybackslash}p{#1}}
\newcolumntype{R}[1]{){\raggedleft\arraybackslash}p{#1}}
\newcolumntype{P}[1]{){\arraybackslash}p{#1}}
\newcolumntype{B}[1]{){\arraybackslash}b{#1}}
\newcolumntype{M}[1]{){\arraybackslash}m{#1}}
\definecolor{label}{gray}{0.75}
\def\unusedattribute#1{\sout{\textcolor{label}{#1}}}
\DeclareRobustCommand*{\xref}{\hyper@normalise\xref@}
\def\xref@#1#2{\hyper@linkurl{#2}{#1}}
\begingroup
\catcode`\_=\active
\gdef_#1{\ensuremath{\sb{\mathrm{#1}}}}
\endgroup
\mathcode`\_=\string"8000
\catcode`\_=12\relax

\usepackage[a4paper,twoside,lmargin=1in,rmargin=1in,tmargin=1in,bmargin=1in,marginparwidth=0.75in]{geometry}
\usepackage{framed}

\definecolor{shadecolor}{gray}{0.95}
\usepackage{longtable}
\usepackage[normalem]{ulem}
\usepackage{fancyvrb}
\usepackage{fancyhdr}
\usepackage{graphicx}
\usepackage{marginnote}

\renewcommand{\@cite}[1]{#1}


\renewcommand*{\marginfont}{\itshape\footnotesize}

\def\Gin@extensions{.pdf,.png,.jpg,.mps,.tif}

  \pagestyle{fancy}

\usepackage[pdftitle={Performance Evaluation of Varying Contention Window Size for Bandwidth Constrained Routing in Adhoc Networks},
 pdfauthor={}]{hyperref}
\hyperbaseurl{}

	 \paperwidth210mm
	 \paperheight297mm
              
\def\@pnumwidth{1.55em}
\def\@tocrmarg {2.55em}
\def\@dotsep{4.5}
\setcounter{tocdepth}{3}
\clubpenalty=8000
\emergencystretch 3em
\hbadness=4000
\hyphenpenalty=400
\pretolerance=750
\tolerance=2000
\vbadness=4000
\widowpenalty=10000

\renewcommand\section{\@startsection {section}{1}{\z@}%
     {-1.75ex \@plus -0.5ex \@minus -.2ex}%
     {0.5ex \@plus .2ex}%
     {\reset@font\Large\bfseries}}
\renewcommand\subsection{\@startsection{subsection}{2}{\z@}%
     {-1.75ex\@plus -0.5ex \@minus- .2ex}%
     {0.5ex \@plus .2ex}%
     {\reset@font\Large}}
\renewcommand\subsubsection{\@startsection{subsubsection}{3}{\z@}%
     {-1.5ex\@plus -0.35ex \@minus -.2ex}%
     {0.5ex \@plus .2ex}%
     {\reset@font\large}}
\renewcommand\paragraph{\@startsection{paragraph}{4}{\z@}%
     {-1ex \@plus-0.35ex \@minus -0.2ex}%
     {0.5ex \@plus .2ex}%
     {\reset@font\normalsize}}
\renewcommand\subparagraph{\@startsection{subparagraph}{5}{\parindent}%
     {1.5ex \@plus1ex \@minus .2ex}%
     {-1em}%
     {\reset@font\normalsize\bfseries}}


\def\l@section#1#2{\addpenalty{\@secpenalty} \addvspace{1.0em plus 1pt}
 \@tempdima 1.5em \begingroup
 \parindent \z@ \rightskip \@pnumwidth 
 \parfillskip -\@pnumwidth 
 \bfseries \leavevmode #1\hfil \hbox to\@pnumwidth{\hss #2}\par
 \endgroup}
\def\l@subsection{\@dottedtocline{2}{1.5em}{2.3em}}
\def\l@subsubsection{\@dottedtocline{3}{3.8em}{3.2em}}
\def\l@paragraph{\@dottedtocline{4}{7.0em}{4.1em}}
\def\l@subparagraph{\@dottedtocline{5}{10em}{5em}}
\@ifundefined{c@section}{\newcounter{section}}{}
\@ifundefined{c@chapter}{\newcounter{chapter}}{}
\newif\if@mainmatter 
\@mainmattertrue
\def\chaptername{Chapter}
\def\frontmatter{%
  \pagenumbering{roman}
  \def\thechapter{\@roman\c@chapter}
  \def\theHchapter{\roman{chapter}}
  \def\thesection{\@roman\c@section}
  \def\theHsection{\roman{section}}
  \def\@chapapp{}%
}
\def\mainmatter{%
  \cleardoublepage
  \def\thechapter{\@arabic\c@chapter}
  \setcounter{chapter}{0}
  \setcounter{section}{0}
  \pagenumbering{arabic}
  \setcounter{secnumdepth}{6}
  \def\@chapapp{\chaptername}%
  \def\theHchapter{\arabic{chapter}}
  \def\thesection{\@arabic\c@section}
  \def\theHsection{\arabic{section}}
}
\def\backmatter{%
  \cleardoublepage
  \setcounter{chapter}{0}
  \setcounter{section}{0}
  \setcounter{secnumdepth}{2}
  \def\@chapapp{\appendixname}%
  \def\thechapter{\@Alph\c@chapter}
  \def\theHchapter{\Alph{chapter}}
  \appendix
}
\newenvironment{bibitemlist}[1]{%
   \list{\@biblabel{\@arabic\c@enumiv}}%
       {\settowidth\labelwidth{\@biblabel{#1}}%
        \leftmargin\labelwidth
        \advance\leftmargin\labelsep
        \@openbib@code
        \usecounter{enumiv}%
        \let\p@enumiv\@empty
        \renewcommand\theenumiv{\@arabic\c@enumiv}%
	}%
  \sloppy
  \clubpenalty4000
  \@clubpenalty \clubpenalty
  \widowpenalty4000%
  \sfcode`\.\@m}%
  {\def\@noitemerr
    {\@latex@warning{Empty `bibitemlist' environment}}%
    \endlist}

\def\tableofcontents{\section*{\contentsname}\@starttoc{toc}}
\parskip0pt
\parindent1em
\def\Panel#1#2#3#4{\multicolumn{#3}{){\columncolor{#2}}#4}{#1}}
\newenvironment{reflist}{%
  \begin{raggedright}\begin{list}{}
  {%
   \setlength{\topsep}{0pt}%
   \setlength{\rightmargin}{0.25in}%
   \setlength{\itemsep}{0pt}%
   \setlength{\itemindent}{0pt}%
   \setlength{\parskip}{0pt}%
   \setlength{\parsep}{2pt}%
   \def\makelabel##1{\itshape ##1}}%
  }
  {\end{list}\end{raggedright}}
\newenvironment{sansreflist}{%
  \begin{raggedright}\begin{list}{}
  {%
   \setlength{\topsep}{0pt}%
   \setlength{\rightmargin}{0.25in}%
   \setlength{\itemindent}{0pt}%
   \setlength{\parskip}{0pt}%
   \setlength{\itemsep}{0pt}%
   \setlength{\parsep}{2pt}%
   \def\makelabel##1{\upshape ##1}}%
  }
  {\end{list}\end{raggedright}}
\newenvironment{specHead}[2]%
 {\vspace{20pt}\hrule\vspace{10pt}%
  \phantomsection\label{#1}\markright{#2}%

  \pdfbookmark[2]{#2}{#1}%
  \hspace{-0.75in}{\bfseries\fontsize{16pt}{18pt}\selectfont#2}%
  }{}
      \def\TheFullDate{2011-03 2011-03-06 (revised: March 2011 06 March 2011)}
\def\TheID{\makeatother }
\def\TheDate{2011-03 2011-03-06}
\title{Performance Evaluation of Varying Contention Window Size for Bandwidth Constrained Routing in Adhoc Networks}
\author{}\makeatletter 
\makeatletter
\newcommand*{\cleartoleftpage}{%
  \clearpage
    \if@twoside
    \ifodd\c@page
      \hbox{}\newpage
      \if@twocolumn
        \hbox{}\newpage
      \fi
    \fi
  \fi
}
\makeatother
\makeatletter
\thispagestyle{empty}
\markright{\@title}\markboth{\@title}{\@author}
\renewcommand\small{\@setfontsize\small{9pt}{11pt}\abovedisplayskip 8.5\p@ plus3\p@ minus4\p@
\belowdisplayskip \abovedisplayskip
\abovedisplayshortskip \z@ plus2\p@
\belowdisplayshortskip 4\p@ plus2\p@ minus2\p@
\def\@listi{\leftmargin\leftmargini
               \topsep 2\p@ plus1\p@ minus1\p@
               \parsep 2\p@ plus\p@ minus\p@
               \itemsep 1pt}
}
\makeatother
\fvset{frame=single,numberblanklines=false,xleftmargin=5mm,xrightmargin=5mm}
\fancyhf{} 
\setlength{\headheight}{14pt}
\fancyhead[LE]{\bfseries\leftmark} 
\fancyhead[RO]{\bfseries\rightmark} 
\fancyfoot[RO]{}
\fancyfoot[CO]{\thepage}
\fancyfoot[LO]{\TheID}
\fancyfoot[LE]{}
\fancyfoot[CE]{\thepage}
\fancyfoot[RE]{\TheID}
\hypersetup{citebordercolor=0.75 0.75 0.75,linkbordercolor=0.75 0.75 0.75,urlbordercolor=0.75 0.75 0.75,bookmarksnumbered=true}
\fancypagestyle{plain}{\fancyhead{}\renewcommand{\headrulewidth}{0pt}}

\date{}
\usepackage{authblk}

\providecommand{\keywords}[1]
{
\footnotesize
  \textbf{\textit{Index terms---}} #1
}

\usepackage{graphicx,xcolor}
\definecolor{GJBlue}{HTML}{273B81}
\definecolor{GJLightBlue}{HTML}{0A9DD9}
\definecolor{GJMediumGrey}{HTML}{6D6E70}
\definecolor{GJLightGrey}{HTML}{929497} 

\renewenvironment{abstract}{%
   \setlength{\parindent}{0pt}\raggedright
   \textcolor{GJMediumGrey}{\rule{\textwidth}{2pt}}
   \vskip16pt
   \textcolor{GJBlue}{\large\bfseries\abstractname\space}
}{%   
   \vskip8pt
   \textcolor{GJMediumGrey}{\rule{\textwidth}{2pt}}
   \vskip16pt
}

\usepackage[absolute,overlay]{textpos}

\makeatother 
      \usepackage{lineno}
      \linenumbers
      
\begin{document}

             \author[1]{Dr. Antony Selvadoss  Thanamani}

             \affil[1]{  S.N.R.Sons College}

\renewcommand\Authands{ and }

\date{\small \em Received: 24 January 2011 Accepted: 19 February 2011 Published: 6 March 2011}

\maketitle


\begin{abstract}
        


Providing bandwidth efficient routing in ad hoc networks is a challenging task. Available bandwidth of nodes is accurately evaluated before finding route from source to destination. Accuracy of available bandwidth is mainly affected by collision and overhead due to the execution of backoff scheme. Existing bandwidth constrained routing uses binary exponential backoff which follows serial transmission and causes unfair channel access. To overcome these, implicit pipelined backoff procedure is proposed to improve the available bandwidth and reduce the overhead associated with the backoff scheme employed in medium access control layer. In this, when two nodes are sharing the channel, the remaining nodes start the channel contention procedure in parallel to transmit next packet. Thus the channel waiting time is reduced. Each node maintains separate contention window for each phase in pipelined backoff. Proper choice of contention window size has great effect on performance of the network. This proposed algorithm is combined with a reactive link disjoint multipath routing protocol called AOMDV (Adhoc Ondemand Multipath Distance Vector) to find the best path based on bandwidth. Experimental results show that this algorithm outperforms existing approach in terms of QoS metrics such as delay, throughput, packet delivery ratio and energy consumption for different contention window sizes.

\end{abstract}


\keywords{BEB, Contention Window, Link disjoint AOMDV, Pipelined Backoff, QoS Routing. Performance Evaluation of Varying Contention Window Size for Bandwidth Co}

\begin{textblock*}{18cm}(1cm,1cm) % {block width} (coords) 
\textcolor{GJBlue}{\LARGE Global Journals \LaTeX\ JournalKaleidoscope\texttrademark}
\end{textblock*}

\begin{textblock*}{18cm}(1.4cm,1.5cm) % {block width} (coords) 
\textcolor{GJBlue}{\footnotesize \\ Artificial Intelligence formulated this projection for compatibility purposes from the original article published at Global Journals. However, this technology is currently in beta. \emph{Therefore, kindly ignore odd layouts, missed formulae, text, tables, or figures.}}
\end{textblock*}


\let\tabcellsep& 	 	 		 
\section[{INTRODUCTION}]{INTRODUCTION}\par
obile ad hoc networks (MANET) consist of a collection of wireless mobile nodes which dynamically exchange data among themselves without any base station or infrastructure. Each node acts as a router to forward traffic and is free to move over a certain area. The wireless mobile nodes may enter as well as leave the network dynamically. MANETS are suitable for emergency situations like natural disasters, military conflicts, medical situations etc. MAC layer protocols use a single channel which is shared by many contending nodes. MAC layer standard called About 1 -S.N.R.Sons College (Autonomous), Coimbatore. Email:sumi\textunderscore karivaradan@yahoo.co.in About 2 -Head, Dept of Computer Science, N.G.M. College (Autonomous), Pollachi. IEEE 802.11 DCF (Distributed Coordinate Function \hyperref[b0]{[1]} is based on CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocol in which nodes listen to the channel before transmission to avoid collision. DCF does not have a central control and known for its asynchronous data transfer. It is used for contention based service. A mobile node uses the virtual carrier sensing mechanism, which utilizes Request-To-Send (RTS) and Clear-To-Send (CTS) exchanges with a Short InterFrame Space (SIFS) for channel reservation. Channel can be viewed in discrete time slots and all nodes are synchronized in time slots. Virtual carrier sensing reduces the probability when two nodes are trying to transmitting simultaneously.\par
Once the node detects that the channel has been free for duration of DCF InterFrame Space (DIFS), it starts a Binary Exponential Backoff (BEB) procedure, i.e., decrementing its back-off counter as long as the channel is idle. If the backoff counter has reduced to zero and the channel is still free, the node begins to transmit. If the channel becomes busy in the middle of the decrement, the node freezes its backoff counter, and resumes the countdown after deferring for a period of time, which is indicated by the Network Allocation Vector (NAV) stored in the transmitted node's packet header \hyperref[b1]{[2]}. It is possible that two or more nodes begin to transmit at the same time. In such a case, collision occurs. Collisions are detected when there is no CTS or acknowledgement (ACK) from the receiver. After collision, all the involved nodes double their CWs (up to a maximum value-CWmax) and compete to gain control of the channel next time. If a node succeeds in channel access, the node resets its CW to CWmin.\par
Due to the limited transmission range of wireless nodes, multi hops are usually needed for a node to exchange information with any other node in the network. For this purpose, a routing protocol is needed that quickly adapts to dynamic topology \hyperref[b2]{[3]}. It is essential to perform routing with maximal throughput and with minimal control overhead. Network layer discovers QoS routes based on MAC layer results. In this paper QoS based routes are traced with bandwidth as a main metric. If the available bandwidth is not estimated accurately, nodes will accept the extra QoS requests and network will be overloaded. To improve the accuracy of available bandwidth, bandwidth loss due to collision probability, back off procedure, idle period synchronization and utilized bandwidth are taken into account in available bandwidth calculation \hyperref[b3]{[4]}. Existing approach uses BEB as the backoff procedure and AODV as the routing protocol. BEB follows serial transmission. Channel idle time and contention overhead is more because of this serial transmission. Nodes go through a channel contention and packet transmission stages sequentially \hyperref[b4]{[5]}. Channel contention stage consumes channel bandwidth. Thus time spent on channel contention is reduced when probability of collision is small. But it is difficult to achieve. Because channel contention cannot be started until the current transmission finishes. Also access to a slot is not uniform. Only the winners repeatedly get the chance to access the channel. This leads to channel capture effect. In a heavily contended network, the collision probability increases which degrades the performance. Hence the main objective is to apply pipelining technique to DCF backoff algorithm to reduce the collision overhead and improve the available bandwidth. In case of AODV, link failure causes the execution route discovery procedure to find alternate route for transmission which leads to packet loss and delay. To overcome, enhanced AOMDV is used to find the routes based on available bandwidth from source to destination.\par
This paper is organized as follows. Section II summarizes related work on backoff algorithms. Section III discusses the pipelined backoff algorithm used in available bandwidth measurement and routing protocol. Section IV shows simulation results and Section V concludes the paper. 
\section[{II.}]{II.} 
\section[{RELATED WORK}]{RELATED WORK}\par
Backoff algorithm is used to reduce collisions when more than one node tries to access the common channel at a time. In MILD (Multiple Increase and Linear Decrease) \hyperref[b5]{[6]}, CW (Contention Window) size is multiplied by 1.5 on collision and decreased by 1 on a successful transmission. It cannot adjust its contention window fast enough because of its linear decrease mechanism. It performs well when the network load is heavy. In \hyperref[b6]{[7]}, authors discussed to enhance the performance of DCF in the presence of noisy channels. Exponential Increase Exponential Decrease (EIED) algorithm discussed in \hyperref[b8]{[8]} increases or decreases CW exponentially by backoff factors r 1 , r d respectively. Performance is good when r 1 =2 and r d =2 1/8 . EIED outperforms BEB and MILD. FCR (Fast Collision Resolution) discussed in \hyperref[b9]{[9]} solves collision more quickly than BEB. When the number of active nodes changes from high to low, LMILD scheme (Linear/Multiplicative Increase Linear Decrease) [10] outperforms the BEB and MILD algorithms for a wide range of network sizes. Authors discussed that the CW resetting scheme causes a very large variation of the CW size and degrades the performance of a network when it is heavily loaded since each new packet starts with minimum CW which is too small for heavy network load. GDCF(Gentle DCF) discussed in  {\ref [11]} is flexible for supporting priority access for different traffic types and is very easy to implement it, as it does not require any changes in control message structure and access procedures . Compared to FCR, GDCF achieves better throughput and fairness. GDCF with smaller number of retransmissions achieves higher throughput for small n and unfair channel access. Throughput drops dramatically when number of nodes (n) increases. P-DCF (Predictive DCF)  {\ref [12]} enables mobile nodes to choose their next backoff times in the collision-free backoff range from the past history of successful transmissions. In DIDD \hyperref[b15]{[13]}, backoff algorithm (Double Increment Double Decrement) CW decreases smoothly after a successful packet transmission. Its throughput is better for CWmin=32 but the delay is high. It achieves better performance than BEB. In NBA \hyperref[b16]{[14]}, large bandwidth is wasted due to collisions. Optimum value of minimum CW depends on number of contending nodes and traffic. Optimum value of CWmin=8.5N-5 ie ?N+?.\par
In BEB \hyperref[b17]{[15,}\hyperref[b18]{16]}, even when number of nodes increase to a large value, nodes will use the same CW size. So lot of collisions occurs and throughput is reduced. At the beginning of each slot a node transmits, if its backoff timer has expired. Otherwise depending on the channel state (idle or busy), the node will count down the backoff counter by 1 or will be frozen at a value. Such an algorithm is embedded in IEEE 802.11 DCF. Delay performance of BEB suffers from collisions which causes more number of retransmissions. It has the problem of channel capture effect which results in channel domination by successful nodes. Adaptive BEB++ \hyperref[b18]{[16]} is designed to consider packet error rate and probability of failed transmission due to noisy channels. After a successful transmission, CW size is set to an optimal value. It adjusts minimum CW size according to active number of nodes. Log based backoff algorithm introduced in \hyperref[b19]{[17]} uses logarithm of current backoff time to calculate next backoff. The difference between two backoff timers is small. So the chance of losing the channel access is less, which improves the throughput performance.\par
Multi Chain Backoff (MCB) algorithm discussed in \hyperref[b20]{[18]} allows nodes to adapt to different congestion levels by using more than one backoff chain together with collision events. MCB can achieve a higher throughput by still maintaining fair channel access than the existing backoff algorithms. Each station maintains a transition diagram to determine its current CW with c chains. When a collision is encountered nodes move to a chain with a larger CWmin and if no collision is detected. It is moved to a chain with smaller CWmin. Conclusion MCB uses multiple backoff chains with minimum CW. Based on collision, it chooses a proper chain. So it offers higher throughput than others. The k-EC (k-round Elimination Contention) scheme exhibits high efficiency and robustness during the collision resolution \hyperref[b21]{[19]}. It is insensitive to the number of active nodes. All the above algorithms follow serial packet transmission which introduces more channel idle time and collision overhead. Most of the bandwidth is wasted due to collision overhead. Hence to reduce the channel idle time and overhead associated with collision, implicit pipelined backoff algorithm is proposed.III. PIPELINED BACKOFF MECHANISM a. Pipelined Available Bandwidth Measurement (Pipelined ABM)\par
Available bandwidth of a node can be improved by considering channel utilization ratio, idle period synchronization and bandwidth loss due to the collision probability. The existing procedure uses BEB to reduce collision \hyperref[b3]{[4]}. 1. Evaluate the capacity of a node and estimate the available bandwidth. 2. Estimate the link's available bandwidth. It depends on channel utilization ratio and idle period synchronization. Let it be E(b(s,r)). It is calculated based on the probability that the channel is free simultaneously at the sender and receiver side. 3. Estimate collision probability Pm for m bits. 4. Collision leads to retransmission of same frames. When collision occurs, implicit pipelined backoff algorithm (IPBA) is executed. This algorithm helps to reduce collisions when more than one node tries to access the common channel. This algorithm is explained in section C. Usually backoff algorithm leads to additional overhead which affects the available bandwidth. Bandwidth lost due to this additional overhead is evaluated. Let it be K. K=(DIFS+ backoff) / T (m) (1) where DIFS is DCF Inter Frame Spacing, T(m) is time between two consecutive frames and backoff is the average number of slots decremented for a frame. The above facts are considered and combined to estimate the available bandwidth which is given below. E final (b(s,r)) = (1-K).(1-Pm).E(b(s,r))\par
(2) where E final (b(s,r)) is the available bandwidth on link by monitoring node and link capacities, Pm is collision probability and K is bandwidth lost due to pipelined backoff scheme. This new available bandwidth is stored in nodes and exchanged with neighbors with the help of Hello messages. Then the routing protocol called AOMDV (Ad hoc Ondemand Multipath Distance Vector) finds the route based on this available bandwidth. 
\section[{b) Pipelined Backoff Mechanism}]{b) Pipelined Backoff Mechanism}\par
The concept of pipelining is to divide the total task into many sub-tasks and executing these sub-tasks in parallel \hyperref[b22]{[20]}. This concept is applied to channel contention procedure of MAC (Channel Access Control) protocol. When two nodes are sharing the channel, the remaining nodes start the channel contention procedure in parallel for the next packet transmission \hyperref[b23]{[21]}. Pipelined backoff hides channel idle time and reduces collision probability. It is also used to control number of contending nodes.\par
When there are few contending nodes in the network, a smaller CW will reduce the channel idle time and channel bandwidth is utilized better. When number of contending nodes is more, CW size is increased to reduce the collision probability and to achieve better throughput. The collision cost is much higher in wireless networks because a node cannot detect collision immediately \hyperref[b24]{[22]}. This pipelined channel contention procedure consumes little bandwidth but improves the performance. Thus Implicit Pipelined Backoff Algorithm (IPBA) is proposed. 
\section[{c) Implicit Pipelined Backoff Mechanism}]{c) Implicit Pipelined Backoff Mechanism}\par
In implicit pipelining there is no separate control channel. It implicitly pipelines the contention resolution stages as phase1 and phase2. Phase1 functions as a filter to select few nodes to contend for channel in Phase2 \hyperref[b24]{[22]} as shown in fig.  {\ref 3}.1. The channel contention can be solved effectively because the number of nodes in phase2 is small. This reduces collision probability and improves channel utilization. 
\section[{1) Phase1}]{1) Phase1}\par
Let FCW be the contention window (First Contention Window) for phase1, bt1 be the backoff timer value. It has FCWmin and FCWmax. The initial value of FCW is FCWmin. The value of bt1 is randomly selected from the interval [0, FCW]. If bt1 is less than or equal to zero the node becomes the pipelined node and enters phase2. After a successful packet transmission bt1 value is reduced by F. The value of F depends on number of successfully transmitted packets (tp) heard by contending nodes in phase1 i.e. F=2 tp -1. If the value of F is larger, then the probability of node becoming a pipelined is more. Bandwidth is wasted when the channel is idle and no nodes are ready to transmit packets. To avoid this loss, bt1 is also linearly decreased by 1 for each idle slot. When bt1 reaches zero it enters into phase2. If any pipelined node wins the channel in phase2, it transmits its packets successfully then set FCW to max [FCW / 2, FCWmin+1], tp to 1 and recalculates bt1 from the interval [0, FCW] and return to phase1. If it looses the channel in phase2, its FCW is set as min [2*FCW+1, FCWmax+1], then recalculates bt1 from [0, FCW], resets tp to 1 and returns to phase1. 
\section[{2) Phase2}]{2) Phase2}\par
Let SCW be the contention window (Second Contention Window) of phase2, bt2 be the backoff timer, SCWmin be the minimum value of contention window and SCWmax be the maximum value of contention window. Initial value of SCW is SCWmin for all nodes entering into phase2. Backoff timer bt2 is calculated from the interval [0, SCW]. As in phase1 bt2 value is also reduced by 1 after each idle slot. Whenever bt2 reaches zero, transmission is allowed. The pipelined node has to wait for the channel to be idle for DIFS duration before backoff procedure starts. If bt2 reaches zero and channel is idle then it begins its transmission. Otherwise bt2 is decremented by 1 after each idle slot. Before bt2 reaches zero if a frame is sent by other nodes then this pipelined node looses channel access and returns to phase1. When collision occurs SCW is doubled and new bt2 is calculated from the interval [0, SCW]. Colliding nodes and pipelined nodes stay in phase2 and repeat the same procedure. If a pipelined node wins the channel, it transmits the packets successfully, then resets FCW to max[FCW / 2, FCWmin+1], SCW to max[SCW / 2, SCWmin+1], tp to 1, calculates bt1 from interval [0, FCW] and go back to phase1. When a pipelined node looses the channel, it doubles FCW and resets SCW, tp to 1, then calculates bt1 and go back to phase1. Thus a node has two ways of reducing bt1. One way is through overheard successful transmission and the other way is after each channel idle slot. The pseudo code for implicit pipelined backoff algorithm is given below. In this algorithm, Contention Window (FCW) size is halved after every successful transmission for a winning node. Due to this channel capture effect is reduced. CW sizes are doubled on collision. Phase1 reduces both channel idle time and collision overhead. Phase2 transmits packets and consumes channel bandwidth. IPBA controls the number of pipelined nodes in phase2 effectively. Now bandwidth loss due this pipelined backoff (K) is estimated and the final available bandwidth is calculated using the formula (2). This method is called as pipelined ABM. This bandwidth is stored in nodes with the help of hello messages. Then the routing protocol finds the route based on bandwidth stored in each node. . 1. For all nodes that want to transmit data packets, do a. Initialize FCW sizes(min,max) and number of packets transmitted (tp). b. Calculate bt1 (backoff timer) randomly from [0,FCW] 2. When a node overhears a successful transmission, increase tp by 1 and decrease bt1 by 2 tp -1. 3. If bt1 is less than 0, node becomes pipelined and enters into Phase2. 4. Else bt1 is reduced by 1 for each idle slot. If it is 0 go to Phase 2. Phase 2:\par
1.For each pipelined node do the following a) Initialize SCW sizes (min ,max), calculate bt2 (backoff timer) randomly from [0,SCW]. b) For each idle slot bt2 is decremented by 1, if bt2 is 0 , transmit a packet, halve FCW, reset tp, go to phase1. c) If pipelined node looses the channel, double FCW upto its maximum, reset SCW, calculate bt1 and initialize tp, go to phase 1. d) If collision occurs SCW is doubled upto its maximum and calculate bt2. 
\section[{d) Discussion on Multipath QoS routing protocol}]{d) Discussion on Multipath QoS routing protocol}\par
Adding QoS to routing protocols help to optimize the performance of traffic on the network. This pipelined backoff algorithm is integrated into a routing protocol called enhanced link disjoint multipath AODV (AOMDV) \hyperref[b25]{[23]} to find the routes from given source to destination based on available bandwidth. Usually frequent route breaks make intermediate nodes to drop packets when there is no immediate alternate path available to the destination. This affects throughput, packet delivery ratio and increases delay. But multipath routing protocol finds multiple paths for a destination during single route discovery process. In case of link failure, source may switch to an alternate path instead of initiating another route discovery. Enhanced AOMDV modifies the base AODV protocol's route discovery mechanism, to enable discovery of multiple link-disjoint paths for a particular source node. To discover linkdisjoint paths \hyperref[b28]{[24]}, each node forwards only one route request towards the destination during the route discovery process; however, it maintains a queue of the previous hop nodes for each RREQ received from a unique neighbor of the source. When a link failure occurs, the node upstream of the link detects the failure, invalidates its routing table entry for that destination and unicasts an RERR message towards the source. Once the source node receives the RERR, it switches its primary path to the next best alternate link-disjoint path.\par
It is designed mainly for highly dynamic ad hoc networks when route breaks and link failures occur frequently. This protocol introduces extra control traffic to monitor alternate paths. 
\section[{IV. SIMULATION RESULTS}]{IV. SIMULATION RESULTS}\par
Performance analysis of pipelined ABM is carried out by varying contention window sizes in phase1. Goal of any QoS is to provide guarantees to the application in terms of throughput, bandwidth, delay, packet delivery ratio (PDR) etc. The proposed algorithm is implemented using NS2 simulator tool \hyperref[b29]{[25]}. The duration of simulation is set to 200s with a grid size of 1000×1000 m. It selects random way point mobility model with CBR (Constant Bit Rate) traffic. This algorithm is tested with 50 nodes. Simulation results present throughput, delay, energy, PDR for different values of CW parameters. Graph helps us to decide the optimal value of CW as . The parameters used to measure the performance are throughput, average end to end delay, energy consumption and packet delivery ratio. To achieve optimum result, system parameters must be selected according to traffic condition. Throughput is calculated as dividing the number of bits transmitted by the time used to transmit these bits. Transmission time includes queuing time, transmission time, interframe space times (SIFS, DIFS etc), control message overhead time and retransmission time. The packet delivery ratio is calculated as the ratio of the data packets delivered to the destination to those transmitted by the CBR traffic. The ability to deliver a high percentage of packets to a destination increases the overall utility of the system. Because the amount of traffic transmitted by the traffic sources varies based on the admission decisions during the simulation. Average end-end delay is calculated based on the average time required to transmit packet from the source to destination. This end-end delay includes delays caused by buffering during route discovery latency, queuing, retransmission delays, propagation and transfer times. Table  {\ref I}      
\section[{V. CONCLUSION}]{V. CONCLUSION}\par
Performance of QoS routing is evaluated based on the bandwidth information obtained from the MAC layer. This paper discusses Implicit Pipelined Backoff Algorithm to reduce the overhead associated with collision and to improve the accuracy of available bandwidth. After estimating the available bandwidth, this algorithm uses AOMDV to find the best path between source and destination with bandwidth as an additional constraint. Pipelined backoff stages consume less bandwidth which is negligible. Pipelined ABM makes the utilization of resources more efficient by minimizing the unnecessary control messages and stopping the transmissions that cannot meet the given QoS\begin{figure}[htbp]
\noindent\textbf{31}\includegraphics[]{image-2.png}
\caption{\label{fig_0}Fig 3 . 1 .}\end{figure}
 \begin{figure}[htbp]
\noindent\textbf{201141}\includegraphics[]{image-3.png}
\caption{\label{fig_2}2011 Fig. 4 . 1}\end{figure}
 \begin{figure}[htbp]
\noindent\textbf{43}\includegraphics[]{image-4.png}
\caption{\label{fig_3}Fig. 4 . 3}\end{figure}
 \begin{figure}[htbp]
\noindent\textbf{45}\includegraphics[]{image-5.png}
\caption{\label{fig_4}Fig. 4 . 5}\end{figure}
 			\footnote{March 2011©2011 Global Journals Inc. (US)} 			\footnote{March 2011} 			\footnote{March 2011©2011 Global Journals Inc. (US)} 			\footnote{March 2011©2011 Global Journals Inc. (US)} 		 		\backmatter  			 			 			  				\begin{bibitemlist}{1}
\bibitem[Wu and Cheng]{b6}\label{b6} 	 		\textit{},  		 			H Wu 		,  		 			S Cheng 		.  		 IEEE 802.11.  		 	 
\bibitem[Wang]{b11}\label{b11} 	 		\textit{},  		 			Chonggang Wang 		.  		 	 
\bibitem[Li]{b12}\label{b12} 	 		\textit{},  		 			Bo Li 		.  		 	 
\bibitem[ ©2011 Global Journals Inc. (US)]{b26}\label{b26} 	 		\textit{},  	 	 		\textit{©2011 Global Journals Inc. (US)}  		 	 
\bibitem[Zhou et al. ()]{b21}\label{b21} 	 		‘A k-round Elimination Contention Scheme for WLANs’.  		 			A Zhou 		,  		 			T Marshall 		,  		 			Lee 		.  	 	 		\textit{IEEE Transactions On Mobile Computing}  		2007.  	 
\bibitem[Ye and Tseng (2006)]{b20}\label{b20} 	 		‘A Multichain Backoff Mechanism for IEEE 802.11 WLANs’.  		 			R Ye 		,  		 			Y.-C Tseng 		.  	 	 		\textit{IEEE Transactions on Vehicular Technology}  		Sept. 2006. 55  (5) .  	 
\bibitem[Manaseer and Ould-Kauoa ()]{b19}\label{b19} 	 		\textit{A New Backoff Algorithm for MAC Protocol in MANETs},  		 			S Manaseer 		,  		 			M Ould-Kauoa 		.  		2005. p. .  	 	 (21st Annual UK Performance Engineering Workshop) 
\bibitem[Deng et al. (2004)]{b10}\label{b10} 	 		‘A new backoff algorithm for the IEEE 802.11 distributed coordination function’.  		 			J Deng 		,  		 			P K Varshney 		,  		 			Z J Haas 		.  	 	 		\textit{Proc. CNDS},  				 (CNDSSandiego, CA)  		2004. Jan. 2004.  	 
\bibitem[Li (2004)]{b13}\label{b13} 	 		\textit{A new collision resolution mechanism to enhance the performance of IEEE 802.11 DCF},  		 			Lemin Li 		.  		July 2004 Page(s. 53 p. .  	 
\bibitem[Kwon et al. ()]{b9}\label{b9} 	 		‘A Novel Channel Access Control Protocol with Fast collision Resolution for wireless LANs’.  		 			Y Kwon 		,  		 			Y Fang 		,  		 			H Latchman 		.  	 	 		\textit{Proc. Infocom Conf},  				 (Infocom Conf)  		2003.  	 
\bibitem[Lohier et al. (2003)]{b2}\label{b2} 	 		\textit{A Reactive QoS Routing Protocol for Ad Hoc Networks},  		 			Stéphane Lohier 		,  		 			Mohammed Sidi 		,  		 			Yacine Senouci 		,  		 			Guy Ghamri-Doudane 		,  		 			Pujolle 		.  		October, 2003.  	 
\bibitem[Chatzimisios et al. (2005)]{b15}\label{b15} 	 		‘A simple and effective backoff scheme for the IEEE 802.11 MAC protocol’.  		 			P Chatzimisios 		,  		 			A C Boucouvalas 		,  		 			V Vitsas 		,  		 			A Vafiadis 		,  		 			A Oikonomidis 		,  		 			P Huang 		.  	 	 		\textit{CITSA},  				 (Orlando, Florida, USA)  		July 2005.  	 
\bibitem[Yang et al. ()]{b24}\label{b24} 	 		‘A Wireless MAC Protocol Using Implicit Pipelining’.  		 			Xue Yang 		,  		 			Member 		,  		 			N H Ieee 		,  		 			Vaidya 		.  	 	 		\textit{Senior Member},  				MAR 2006. 5.  	 
\bibitem[Marek Natkaniec Andrzej and Pach ()]{b17}\label{b17} 	 		‘An analysis of the Back-Off Mechanism Used in IEEE 802.11 Networks’.  		 			R Marek Natkaniec Andrzej 		,  		 			Pach 		.  	 	 		\textit{Proc the Fifth IEEE Symposium on ISCC},  				 (the Fifth IEEE Symposium on ISCC)  		2000.  	 
\bibitem[Hu et al. (2005)]{b18}\label{b18} 	 		\textit{An Analysis of the Binary Exponential Backoff Algorithm in Distributed MAC Protocols},  		 			Chunyu Hu 		,  		 			H Kim 		,  		 			J C Hou 		.  		July 2005.  	 
\bibitem[Sarr et al. ()]{b3}\label{b3} 	 		‘Bandwidth Estimation for IEEE 802.11-Based Ad Hoc Networks’.  		 			Cheikh Sarr 		,  		 			Claude Chaudet 		,  		 			Guillaume Chelius 		,  		 			Isabelle Gue´ Rin Lassous 		.  	 	 		\textit{IEEE TRANS ON MOBILE COMPUTING}  		OCT 2008. 7  (10) .  	 
\bibitem[Distributed Coordination Function (DCF): Analysis and Enhancement Proc. IEEE ICC (2002)]{b7}\label{b7} 	 		‘Distributed Coordination Function (DCF): Analysis and Enhancement’.  	 	 		\textit{Proc. IEEE ICC},  				 (IEEE ICC)  		Apr. 2002. 1 p. .  	 
\bibitem[Yang and Vaidya (2002)]{b23}\label{b23} 	 		\textit{DSCR -A Wireless MAC Protocol Using Implicit Pipelining},  		 			Xue Yang 		,  		 			N H Vaidya 		.  		December 2002.  		 			Coordinated Science Laboratory, University of Illinois 		 	 	 (Technical report) 
\bibitem[Sambasivam et al. ()]{b28}\label{b28} 	 		‘Dynamically Adaptive Multipath Routing based on AODV’.  		 			Perumal Sambasivam 		,  		 			Ashwin Murthy 		,  		 			E M Belding-Royer 		.  	 	 		\textit{Proc. 3rd Annual MAHN},  				 (3rd Annual MAHN)  		2004.  	 
\bibitem[Song et al. ()]{b8}\label{b8} 	 		‘Enhancement of IEEE 802.11 distributed coordination function with exponential increase exponential decrease backoff algorithm’.  		 			N Song 		,  		 			B Kwak 		,  		 			J Song 		,  		 			L E Miller 		.  	 	 		\textit{Proc. IEEE VTC 2003-Spring},  				 (IEEE VTC 2003-Spring)  		2003.  	 
\bibitem[Yang and Vaidya ()]{b22}\label{b22} 	 		‘Explicit and Implicit Pipelining for Wireless Channel Access Control’.  		 			X Yang 		,  		 			N H Vaidya 		.  	 	 		\textit{Proc IEEE Seminar Vehicular Technology Conf., Fall},  				 (IEEE Seminar Vehicular Technology Conf., Fall)  		2003.  	 
\bibitem[Global Journal of Computer Science and Technology Volume XI Issue III Version I (2011)]{b27}\label{b27} 	 		\textit{Global Journal of Computer Science and Technology Volume XI Issue III Version I},  		77 March 2011.  	 
\bibitem[Bharghavan et al. ()]{b5}\label{b5} 	 		‘MACAW: A Media Access Control Protocol for Wireless LANs’.  		 			A Bharghavan 		,  		 			S Demers 		,  		 			L Shenker 		,  		 			Zhang 		.  	 	 		\textit{Proc. SIGCOMM '94 Conf},  				 (SIGCOMM '94 Conf)  		1994. ACM. p. .  	 
\bibitem[Taifour et al. ()]{b16}\label{b16} 	 		\textit{Neighbourhood Backoff Algorithm for Optimizing Bandwidth in Single Hop Wireless Ad-Hoc Networks},  		 			Mahmoud Taifour 		,  		 			Farid Na®\textunderscore T-Abdesselam 		,  		 			David Simplot-Ryl 		.  		2005.  		 			LIFL/IRCiCA Laboratory -INRIA POPS Project 		 	 
\bibitem[NS manual]{b29}\label{b29} 	 		 \url{http://www.isi.edu/nsnam/ns/ns-documentation.html}  		\textit{NS manual},  				 	 
\bibitem[Samir and Das (2001)]{b25}\label{b25} 	 		‘Ondemand Multipath Distance Vector Routing in Ad Hoc Networks’.  		 			Mahesh K Marina Samir 		,  		 			R Das 		.  	 	 		\textit{Proceedings of the 9 th International IEEE Conference on Network Protocols (ICNP)},  				 (the 9 th International IEEE Conference on Network Protocols (ICNP))  		November 2001.  	 
\bibitem[Choi et al. (2005)]{b14}\label{b14} 	 		\textit{P-DCF: Enhanced Backoff Scheme for the IEEE 802.11 DCF'', IEEE VTC 2005-Spring},  		 			Nakjung Choi 		,  		 			Yongho Seok 		,  		 			Yanghee Choi 		,  		 			Gowoon Lee 		,  		 			Sungmann Kim 		,  		 			Hanwook Jung 		.  		May, 2005. Stockholm, Sweden.  	 
\bibitem[Bianchi (2000)]{b0}\label{b0} 	 		‘Performance analysis of the IEEE 802.11 distributed coordination function’.  		 			G Bianchi 		.  	 	 		\textit{IEEE Journal on Selected areas in Communications}  		March 2000. 18  (3) .  	 
\bibitem[Yang and Vaidya (2002)]{b4}\label{b4} 	 		\textit{Pipelined Packet Scheduling in Wireless LANs},  		 			X Yang 		,  		 			N H Vaidya 		.  		Aug. 2002.  		 			Coordinated Science Laboratory, Univ. of Illinois at Urbana-Champaign 		 	 	 (technical report) 
\bibitem[Gong (2006)]{b1}\label{b1} 	 		‘Quality of Service Aware Routing Protocols for Mobile Ad Hoc Networks’.  		 			Shan Gong 		.  	 	 		\textit{MS theses},  				August 2006.  	 
\end{bibitemlist}
 			 		 	 
\end{document}
