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\title{Smart Acknowledgement Distributed Channel Access Scheme for TCP in Manets}
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             \author[1]{D.  Sunitha}

             \author[2]{Dr. A.  Nagaraju}

             \author[3]{Dr. G.  Narsimha}

             \affil[1]{  }

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\date{\small \em Received: 8 February 2015 Accepted: 5 March 2015 Published: 15 March 2015}

\maketitle


\begin{abstract}
        


TCP upon wireless networks is most challenging issue because of random losses and ACK interference. Also, TCP suffers from performance declination in terms of creating delay and overhead in network because of poor characteristics of wireless channel. In order to overcome these issues, we proposed a Smart Acknowledgement Distributed Channel Access (SADCA) scheme for TCP in MANETs. In the proposed scheme, first a separate Access Category (AC) for data less TCP acknowledgement packets is used and then it is assigned with highest priority. In this way, delay during transmission of packet can be reduced and also packet can be acknowledged immediately. Also, to increase the performance, delay window size can be adjusted by considering the parameters such as transmission rate, number of hops, and channel occupied ratio (COR). Hence the proposed scheme helps to avoid any kind of delay and overhead for sending TCP acknowledgement

\end{abstract}


\keywords{distributed channel access; access category; TCP smart acknowledgement; manets.}

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\let\tabcellsep& 	 	 		 
\section[{Introduction obile}]{Introduction obile}\par
Ad-hoc Network(MANET) is an autonomous infrastructure-less system with wireless links connecting mobile nodes each operating as an end system as well as a router to forward packets and are free to move and form a network without any base stations. As mobile nodes communication is faster, it has a wide application in military applications, emergent operations, personal electronic device networking, and civilian applications like an ad-hoc meeting or an ad-hoc classroom. MANET's special characteristics like dynamic topologies, bandwidth constrained, variable capacity links, energy constrained operation, limited physical security make it susceptible to various attacks. In addition, jamming occurs in unreliable wireless links and eavesdropping due to their inherent broa dcast nature. Mobile devices' bandwidth, computing power, as well as battery power constraints causes application-specific trade-offs between devices' security and resource consumption. Behavior anomalies like advertising bogus routes are difficult to detect due to mobility \hyperref[b0]{[1]}.\par
The Transmission Control Protocol (TCP), the most commonly used reliable transport protocol in the internet, provide end-to-end reliable transmission as well as fair congestion control so as to share network resources efficiently \hyperref[b1]{[2]}. Congestion control is a necessity for MANET since it operates in bandwidth constrained conditions.\par
TCP, in today's internet has poor performance and in MANETs is worsen by contention with increasing UDP-based high priority multimedia traffic and the class differentiation introduced in current QoS protocols, which results into TCP starvation and increased spurious timeouts \hyperref[b2]{[3]}. The TCP usage over wireless networks rise to problems due to the different characteristics of wireless links with respect to wired ones, in terms of less reliability and time-variant behavior, fading / shadowing problems, node mobility, hand-offs, limited available bandwidth and large RTTs \hyperref[b4]{[5]}. TCP performs reliably in traditional wired and stationary networks, but network congestion induces losses. Moreover, if the router waiting queues are full or nearly full, the packets received are dropped, thereby wired network losses are viewed as an indication of congestion. But in wireless networks the losses occur frequently for various causes such as interference, node mobility or poor link quality.\par
In MANETs, data transmission failures due to node mobility, interference, poor link quality, etc lead often to the congestion control activation by TCP protocol unnecessarily which degrades the performance of TCP in MANETs \hyperref[b1]{[2,}\hyperref[b3]{4,}\hyperref[b5]{6]} .\par
The TCP reliability guarantees, TCP sender will forward each packet issued by it to the addressee node by a system of acknowledgements \hyperref[b3]{[4]}. In TCP protocol, cumulative acknowledgements (ACKs) are sent by the TCP receiver for successfully received segments so as to let the TCP sender to find out the segments which have successfully received. The TCP sender determines the loss of packet either by several duplicate ACKs arrival, triggering a fast retransmission, or by the absence of an ACK for a timeout interval, thereby the TCP retransmits the lost packets, and simultaneously invokes congestion control by reducing its congestion window size and backing off its retransmission time for compensating packet losses. These reduce the level of congestion on the intermediate links \hyperref[b6]{[7]}.\par
The TCP Acknowledgements may return collide with their corresponding data packets in particular if the number of network nodes becomes vital. Such a large number of TCP ACK packets come into contention with TCP packets leads to intra-flow contention \hyperref[b3]{[4]}.\par
As an extension to this work, we propose to design a smart acknowledgement distributed channel access scheme for TCP in order to reduce the delay and overhead of sending TCP acknowledgements. 
\section[{II.}]{II.} 
\section[{Literature Review}]{Literature Review}\par
Chien-Chia Chen et al \hyperref[b1]{[2]} presented Combo Coding, a novel coding scheme combining intra-and inter-flow coding and a novel loss adaptation algorithm was featured. Combo Coding decreases the data and ACKs' interference within a TCP session taking advantage of the benefits of both types of codes, and also robustness to high link losses is exhibited. 2 Mbps good put is achieved by Combo Coding successfully with 30\% per link packet loss rate; whereas TCP-New Reno with no coding delivers only 200 Kbps. Combo Coding over 2 paths provides a lower good put than that over a single path due to a higher overhead due to extra contentions as in the 20s-50s interval.\par
Sofiane Hamrioui et al \hyperref[b3]{[4]} suggested an improvement of the Transmission Control Protocol (TCP), called Improvement of the Acknowledgement mechanism of TCP (IA-TCP), for MANET's better performance. Based on number of nodes, mobility and the communication distance between these nodes, IA-TCP delays TCP's acknowledgements packets. However, only throughput and end-to-end delay parameters are concerned. However, there is degradation of the TCP parameters performance.\par
Mohammad Amin Kheirandish Fard et al \hyperref[b9]{[10]} proposed an end-to-end sender-side approach classifying congestion loss, wireless channel loss and link failure loss by queue usage estimation. Queue usage is calculated using relative One-way Trip Time.\par
Congestion loss is estimated using packet losses with queue usage rate greater than predefined threshold whereas non-congestion loss is when queue usage is less than threshold. Non congestion loss recognized by three duplicate ack labels loss caused by wireless channel error as it indicate the route existence between communicating end point that duplicate ACKs moved along.\par
Deguang Le et al \hyperref[b10]{[11]} proposed a new crosslayer approach introducing a mobility detection element in the network layer to communicate with the transport layer for optimizing TCP operations. This approach preserves the end to end TCP semantics since end point changes are only made. Unlike other networks utilizing either transport or network layer alone without much cross-layer cooperation, this approach enable mobility information in TCP. However, RTO is reduced significantly compared to the standard TCP/MIPv6 as soon as the handover termination.\par
Consolee Mbarushimana et al \hyperref[b11]{[12]} proposed a novel TCP-friendly scheme, IEDCA, for enhancing IEEE 802.11e EDCA mechanism by assigning the highest priority to TCP acknowledgement packets. The proposed scheme improves TCP performance significantly while having very negligible effects on voice traffic. However, the voice traffic dropped by buffer overflow or when the retry threshold is exceeded is higher in EDCA.\par
Toktam Mahmoodi et al \hyperref[b12]{[13]} presented and assessed a cross-layer solution for a node for faster adaption of lower-layer characteristics like the coding rate and local ARQ retransmissions threshold according to the detected TCP flavor, so as to optimize the end-toend performance of the download for that utilized flavor.\par
The proposed scheme has considerable potential to improve the overall download throughput, without burdening the server and requiring no changes to existing TCP implementations. However, end-to-end throughput decreases with increasing propagation distance.\par
Myungjin Lee et al \hyperref[b13]{[14]} proposed a path recovery notification (TCP-PRN) mechanism for avoiding performance degradation while handoff. Despite of being attained performance improvement while handoff, Freeze-TCP deployment in real environment is difficult due to obstacles in detecting accurate handoff time and the vulnerability of high variation in the round trip time (RTT). The proposed protocol restore congestion window avoiding it to reduce or immediately initiate slow start algorithm to recover lost packets. However, the handoff prediction is difficult and the variation of RTT is higher.\par
Ammar Mohammed AI-Jubari and Mohamed Othman \hyperref[b14]{[15]} proposed a new delay-ACK algorithm for TCP performance enhancement over multi-hop wireless networks. According to factors like TCP startup phase, transmission rate, packet loss event, and number of hops, the optimal delayed ACK window is achieved dynamically as like before. The dynamic adaptive strategy's objective is enabling TCP receiver to adjust itself in terms of the data to ACK ratio. The scheme enhances TCP performance, attaining up to 233 \% performance gain, over multi-hop wireless networks, compared to the regular TCP. However, the burst transmission occurs at the sender triggered by delayed In our previous work \hyperref[b17]{[18]}, a cross-layer based approach for improving TCP performance in Multihop Mobile Ad-hoc Networks (MANETs) is proposed. The proposed mechanism triggers congestion whenever the channel occupied ratio (COR) reaches a maximum threshold value and the received signal strength is less than a minimum threshold value. Following it, congestion control scheme controls the data sending rate of the sender by determining available bandwidth, delay of its link and COR. Further, a fair resource allocation scheme is put forwarded.Volume XV Issue VII Version I Year 2015 ( E )\par
ACK. The burstiness increases the packet loss and potentially affects TCP performance. 
\section[{III.}]{III.} 
\section[{Proposed Solution a) Overview}]{Proposed Solution a) Overview}\par
The delay in packet transmission leads to loss of packet as well as throughput degradation. Hence we use a separate access category for data less TCP acknowledgement packets and assumed higher priority to them \hyperref[b11]{[12]}. Hence delay in packet transmission can be reduced and packets are acknowledged instantaneously. Here higher congestion window value is attained than by TCP over Enhanced Distributed Channel Access (EDCA). Further improvements can be made by adjusting the delay window size by considering channel conditions like transmission rate, slow start phase, number of hops and packet lost event \hyperref[b14]{[15]}. Here the number of acknowledgement packets can be reduced by generating the acknowledgement packets after attaining optimal dynamic delay window. Therefore receiver can adapt according to various delays. 
\section[{b) Estimation of Metrics i. Probability of Successful Transmission :}]{b) Estimation of Metrics i. Probability of Successful Transmission :}\par
Most of the previous studies propose the probability of successful transmission based on analytical skills to compute delay and throughput that can be attained by different traffic categories in IEEE 802.11e for which they mainly considered Markov model. In this type of model successful transmission is given as below:?= 2 1+V+pV ? (2p) i n ?1 i=0\textbf{(1)}\par
V represents initial contention window during backoff stage, p represents the conditional collision probability, and n represents maximum backoff stage. Also the transmission probability k ? of a station of Access Category (AC) k can be given as below:? k = 2 1+V k +p k V k ? (2p k ) i n k ?1 i=0\textbf{(2)}\par
Based on above equation, similar expression can be obtained for throughput T k which is attainable by an access category k as belowT k = n k ? k (l?p k )l p(t)H (t) +p(c)H (s) +p(e) ?\textbf{(3)}\par
Where l represents average transmission time of payload for access category 'k'. p(t), p(c) and p(e) are the probabilities of a slot time contains successful transmission, collision, and channel being idle respectively. H(s), H(t) and ? represents average slot length of successful transmission, collision and channel being inactive respectively. From the above expressions, it can be observed that probability of successful transmission for any AC is inversely proportional to contention window V. Hence station with traffic in high priority AC will have low values of V which in turn will have higher chance of transmitting their data than stations with best effort and will have better throughput. But this case is not applicable for TCP traffic. For TCP traffic, a packet is considered to be successfully transmitted in case TCP ACK is received by the sender before the retransmission time is over. Based on the probability idea of successful transmission given by equation ( \hyperref[formula_2]{2}), successful transmission probability in case of TCP traffic is a combination of probability of successfully transmitted data packet as well as probability of successfully received ACK packet. Hence, for TCP traffic belonging to AC1, probability of successful transmission can be given as below:?? TCP = 4 ?1+V 1 +p 1 V 1 ? (2p i ) i n 1 ?1 i=0 ? 2\textbf{(4)}\par
Here assume that data and ACK have the same transmission probability, since they belong to the same access category and moreover delayed ACK option is not used. Hence TCP throughput is different from any other best attempt throughput which is accessible by equation ( \hyperref[formula_3]{3}), as it depends on the value ?TCP which is given in the equation ( \hyperref[formula_4]{4})\par
ii. Channel Occupied Ratio (COR) COR is defined as the ratio of total lengths of busy periods to the total transmission time. . Consider T T denotes the total transmission time and T b represents total length of busy periods. Hence COR can be given as below:?????? = ?? ?? ?? ?? (5)\par
By considering channel utilization factor, a threshold value Th COR , it can be given as below:?????? ? C U (COR ? Th COR ) (6)\par
Where, C U denotes channel utilization factor and it is the measure of ratio of channel busyness time for successful transmissions to the total time T T . 
\section[{c) Smart Acknowledgement Distributed Channel Access Scheme}]{c) Smart Acknowledgement Distributed Channel Access Scheme}\par
This section describes the proposed Smart Acknowledgement Distributed Channel Access (SADCA). The main aim of the proposed technique is to maximize the throughput without creating any delay in the network.\par
In this technique, an additional fifth access category saved for data less TCP ACK is defined. This new AC is assigned with highest priority. By placing data less TCP ACKs in top priority access category, probability of transmitting them on time is also maximized. Since the TCP ACK transmission probability tends to 1, transmission probability of TCP traffic can be expressed by equation \hyperref[b1]{(2)}. In similar way, the possible TCP throughput can be obtained by equation( \hyperref[formula_3]{3}) with the exception that H s increases by the value equal to time required to transfer both TCP ACK as well as MAC control packets that go along with it. By utilizing this method, the probability that all the TCP packets transmitted get acknowledged are increased. The underlying principle of this method make use of transport layer to control the volume of TCP ACKs on the channel. The volume of TCP ACKs permitted on the channel matches the volume of TCP data which is successfully transmitted and it is independent of the type of other traffic struggling for the same medium. To avoid any kind of congestion due to retransmission COR is validated inside the network using equation (  {\ref 5}) and (  {\ref 6}), if in case the delay due to congestion is found. 
\section[{The implementation of the SADCA can be explained in steps as below:}]{The implementation of the SADCA can be explained in steps as below:}\par
Step 1 : In the first step, type of service (ToS) is usually applied at the application layer, however TCP ACKs originate from the transport layer, hence transport layer is responsible for assigning a proper ToS to them.\par
Step 2 : Since transport layer automatically assign the best effort ToS to TCP ACKs, a different ToS need to be assigned to them to distinguish them from best effort traffic.\par
Step 3 : To make the process simple, ToS value (  {\ref 224}) is assigned to the data less TCP ACK at the transport layer when they are about to sent to the lower layer.\par
Step 4 : The MAC layer describes 8 user priority levels which are used to arrange the different data packets into different ACs.\par
Step 5 : By considering 224 as their transport layer ToS, TCP ACK will be allocated to the user 7.\par
Step 6 : Also a fifth AC is defined corresponding to MAC user priority value of 7 and hence collect the TCP ACKs.\par
The mapping of client priority (CP) to AC in SADCA is shown in Table \hyperref[tab_0]{1}. Hence an additional traffic queue is obtained in SADCA as shown in Fig.  {\ref 1}. The proposed aim is to allow TCP ACKs priority to the medium. After that priority is assigned to the new AC having smaller values of AIFS, CWmin and CWmax compared to the existing higher priority voice traffic as shown in Table \hyperref[tab_1]{2}.  The improvement in the proposed technique can be shown with the following example:\par
In case, TCP ACK is produced at the same time as the voice traffic, then station T S gains the medium contention because these TCP ACKs are in an AC with higher priority than voice. Hence it can be said that T S have more chance to transmit the TCP ACK before timeout and hence avoid the retransmission at the source. If the TCP ACK is generated before timeout, and then it avoids any kind of retransmission at the source.\par
Also if TCP ACK is generated after the VoIP conversation started, then it will have a good opportunity to compete for the medium at the end of the next TXOP of the VoIP stations. Hence it can be said that, there is a high chance that ACK will be received within the RTO limit. Also retransmission can be avoided.     Fig.  {\ref 4} shows the delivery ratio of SADCA-TCP and TCP techniques for different number of flows scenario. We can conclude that the delivery ratio of SADCA -TCP has 3\% of higher than TCP. Fig. \hyperref[fig_2]{5} shows the throughput of SADCA-TCP and TCP techniques for different number of flows scenario. We can conclude that the throughput of SADCA-TCP has 45\% of higher than TCP. The simulation settings and parameters are summarized in Table \hyperref[tab_4]{4}.  Fig.  {\ref 8} shows the delivery ratio of SADCA-TCP and TCP techniques for different number of flows scenario. We can conclude that the delivery ratio of SADCA -TCP has 2\% of higher than TCP. Fig.  {\ref 9} shows the throughput of SADCA-TCP and TCP techniques for different number of flows scenario. 
\section[{IV.}]{IV.} 
\section[{Simulation Results}]{Simulation Results}\par
We can conclude that the throughput of SADCA-TCP has 37\% of higher than TCP.\par
V. 
\section[{Conclusion}]{Conclusion}\par
In this paper we have proposed a Smart Acknowledgement Distributed Channel Access (SADCA) scheme for TCP in MANETs. In the proposed scheme, first a separate access category for data less TCP acknowledgement packets is used and also it is assigned with highest priority. As the TCP ACK is assigned with new AC with highest priority, it has maximum probability of successful transmission by making efficient utilization of contention window during backoff stage. In this way, delay during transmission of packet can be reduced and also packet can be acknowledged immediately. Also, to increase the performance, delay window size can be adjusted for optimization purpose by considering the parameters such as transmission rate, number of hops, and congestion occupied ratio (COR). Hence the proposed scheme helps to avoid any kind of delay and overhead for sending TCP acknowledgement\begin{figure}[htbp]
\noindent\textbf{12}\includegraphics[]{image-2.png}
\caption{\label{fig_0}Fig. 1 :Fig . 2 :}\end{figure}
 \begin{figure}[htbp]
\noindent\textbf{34}\includegraphics[]{image-3.png}
\caption{\label{fig_1}Fig. 3 :Fig. 4 :}\end{figure}
 \begin{figure}[htbp]
\noindent\textbf{5}\includegraphics[]{image-4.png}
\caption{\label{fig_2}Fig. 5 :}\end{figure}
 \begin{figure}[htbp]
\noindent\textbf{6}\includegraphics[]{image-5.png}
\caption{\label{fig_3}Fig. 6 :}\end{figure}
 \begin{figure}[htbp]
\noindent\textbf{789}\includegraphics[]{image-6.png}
\caption{\label{fig_4}Fig. 7 :Fig. 8 :Fig. 9 :}\end{figure}
 \begin{figure}[htbp]
\noindent\textbf{1} \par 
\begin{longtable}{P{0.17761194029850746\textwidth}P{0.17761194029850746\textwidth}P{0.49477611940298505\textwidth}}
Client Priority(CP)\tabcellsep Access Category(AC)\tabcellsep Designation\\
1\tabcellsep 0\tabcellsep Background\\
2\tabcellsep 0\tabcellsep Background\\
0\tabcellsep 1\tabcellsep Best Effort\\
3\tabcellsep 1\tabcellsep Best Effort\\
4\tabcellsep 2\tabcellsep Video\\
5\tabcellsep 2\tabcellsep Video\\
6\tabcellsep 3\tabcellsep Voice\\
7\tabcellsep 4\tabcellsep TCP ACK\\
8\tabcellsep 1\tabcellsep COR\end{longtable} \par
 
\caption{\label{tab_0}Table 1 :}\end{figure}
 \begin{figure}[htbp]
\noindent\textbf{2} \par 
\begin{longtable}{P{0.29041666666666666\textwidth}P{0.18416666666666667\textwidth}P{0.14875\textwidth}P{0.035416666666666666\textwidth}P{0.19125\textwidth}}
\tabcellsep \tabcellsep in SADCA\tabcellsep \tabcellsep \\
AC\tabcellsep \multicolumn{3}{l}{CW mi CW max AIFSN}\tabcellsep TXOP limit\\
Voice\tabcellsep 7\tabcellsep 15\tabcellsep 2\tabcellsep 3264\\
Video\tabcellsep 15\tabcellsep 31\tabcellsep 2\tabcellsep 6016\\
Best Effort\tabcellsep 31\tabcellsep 1023\tabcellsep 3\tabcellsep 0\\
Backgroun\tabcellsep 31\tabcellsep 1023\tabcellsep 7\tabcellsep 3264\\
d TCP ACK\tabcellsep 3\tabcellsep 7\tabcellsep 1\tabcellsep 3264\end{longtable} \par
 
\caption{\label{tab_1}Table 2 :}\end{figure}
 \begin{figure}[htbp]
\noindent\textbf{} \par 
\begin{longtable}{P{0.85\textwidth}}
Smart Acknowledgement Distributed Channel Access Scheme for TCP in Manets\\
a) Simulation Setup NS-2 simulator is used to simulate the Smart Acknowledgement Distributed Channel Access scheme for TCP (SADCA-TCP) protocol. In our simulation, the channel capacity of all mobile hosts is Queue 0 Backoff AIFS AC0 Scheduler (Resolve virtual Collision) Transmission Queue 1 Queue 2 Queue 3 Backoff AIFS AC2 Backoff AIFS AC3 Backoff AIFS AC4 Backoff AIFS AC1 set to 2 Queue 4 Background Best Effort Video Voice TCP ACK\end{longtable} \par
 
\caption{\label{tab_2}}\end{figure}
 \begin{figure}[htbp]
\noindent\textbf{3} \par 
\begin{longtable}{P{0.5648387096774193\textwidth}P{0.28516129032258064\textwidth}}
No. of Nodes\tabcellsep 9\\
Area Size\tabcellsep 1700 X 300\\
Mac\tabcellsep 8021.11\\
Radio Range\tabcellsep 250m\\
Simulation Time\tabcellsep 300 sec\\
Traffic Source\tabcellsep FTP\\
Packet Size\tabcellsep 1000 bytes\\
No. of Flows\tabcellsep 1 to 8\\
Routing Protocol\tabcellsep AODV\end{longtable} \par
  {\small\itshape [Note: The simulation results are given below:]} 
\caption{\label{tab_3}Table 3 :}\end{figure}
 \begin{figure}[htbp]
\noindent\textbf{4} \par 
\begin{longtable}{P{0.5931111111111111\textwidth}P{0.2568888888888889\textwidth}}
No. of Nodes\tabcellsep 50\\
Area Size\tabcellsep 1500 X 300\\
Mac\tabcellsep 8021.11\\
Radio Range\tabcellsep 250m\\
Simulation Time\tabcellsep 300 sec\\
Pause time\tabcellsep 5 seconds\\
Speed\tabcellsep 10 m/s\\
Traffic Source\tabcellsep FTP\\
Packet Size\tabcellsep 512 bytes\\
No. of Flows\tabcellsep 1 to 10\\
Routing Protocol\tabcellsep AODV\\
\multicolumn{2}{l}{The simulation results are given below:}\end{longtable} \par
 
\caption{\label{tab_4}Table 4 :}\end{figure}
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