Enhanced NRC-LD for Improving TCP Performance over Wireless Network

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Enhanced NRC-LD for Improving TCP Performance over

Wireless Network

Prof. J. VijiPriya

, Dr.S. Suppiah

1

Department of CSE, A M S Engineering College, Namakkal, TamilNadu, India 2

Department of Civil, E S Engineering College, Villupuram, TamilNadu, India

ABSTRACT

Internet performance is affected by Transmission Control Protocol (TCP) performance degradation in wireless network due to packet loss in transmission. The existing TCP variants misinterpret this loss to congestion and invokes congestion control .This paper presents TCP variants and Enhanced TCP variants with Loss Differentiation algorithms to differentiate congestion loss from wireless link loss. The proposed Newton Raphson Congestion Control with Loss Discrimation (NRC-LD) is a modification of the congestion control mechanism at the sender. TCP sender computes actual sending rate and flight size. If the current actual sending rate is less than flight size, congestion loss Else, wireless loss and retransmits the lost packet without reducing congestion window. The TCP NRC-LD is compared with many TCP versions to analyze its performance using NS2. The proposed scheme provides better performance based on network criteria.

Keywords:

1.

INTRODUCTION

Most of Internet traffic is carried out by Transmission Control Protocol (TCP) which was designed and tuned to perform very well in wired networks, It provides reliability connection, utilize the available bandwidth and avoid overloading the network by its congestion control mechanism. Wireless networking technologies is being growing rapidly. Internet-enabled wireless devices such as cellular phones and personal digital assistants utilize the wireless access network to connect with wired network. In this case, TCP is not well-suited for wired/wireless network to handle packet losses due to the nature of it packet loss. In the wired network, packet losses are due to the network congestion. Packet losses are due to handover operation, variable bandwidth, dynamic network topology and host mobility in wireless network.

Wireless Networks offer challenges to TCP’s congestion control mechanism which can not distinguish between congestion loss and wireless losses. Many proposals have been used to deal with this issue either end-to- end approach or Network Feedback approach. In Wired Network hosts are in fixed position and are connected by cables .There is least transmission Bit Error Rate due to interference from the environment but the hosts on wireless networks frequently move while communicating and share the media for communication. TCP provides reliable end-to-end delivery of data over wired networks but TCP performance degrades significantly in Wireless Network because TCP considers any packet loss and/or delay as a congestion signal.TCP congestion control algorithm by reducing the transmission rate is not suitable in wireless network. In wireless network, Non-congestion losses and/or delays occur. However, it results in low bandwidth utilization, unnecessary retransmission and low throughput.

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In the case of wireless loss, the TCP receiver sends 3 duplicate ACKs to TCP Sender. The TCP sender retransmits the missing packets and unnecessarily retransmitting a delayed or mis-ordered segment. There is no reliance on the Fast Retransmit algorithm to detect the wireless link loss. Modified Fast Retransmit algorithm is important because duplicate ACKs are received when operating over a highly loss link. The proposed NRC-PLD is a modification of the congestion control mechanism at the sender. When 3 duplicate ACKs are received, the TCP sender invokes Modified Fast Retransmission and computes and compares actual sending rate and flight size. If the current actual sending rate is less than flight size, it is a congestion loss and retransmits the packet with reducing congestion window Else, wireless loss and retransmits the packet without reducing congestion window. Consequently, The TCP sender enters into Modified Fast Recovery, leading to higher bandwidth utilization, better throughput and fairness.

2. RELATED WORKS

2.1 Congestion Control Algorithms

High-speed TCP protocols [1, 2] can be broadly categorized into two categories based on how they sense congestion in the network: Loss-based protocols use packet loss in the network to detect congestion where as delay-based protocols use queuing delays at the routers, in addition to loss, to detect congestion. Loss based protocols use packet drop probability as the main factor for adjusting the window size. Loss based TCP protocols variants use congestion control algorithms that were developed initially and are still used. These TCP variants are more aggressive than the delay based TCP protocols [3]. All the protocols we have considered in our experiments are loss-based protocols.Hamilton TCP (H-TCP) uses the time between packet drops to adjust the congestion window. It uses the following function to decrement its congestion window: cwnd = cwnd * β. Where β is such that 0.5 < β < 0.8.H-TCP adopts an adaptive back off strategy to decrement the congestion window when it detects congestion. It uses the ratio of the minimum-observed RTT to the maximum-observed RTT to compute the new congestion window value.

TCP-Hybla scales the window increment rule to ensure fairness among the flows with different RTTs. TCP-Hybla behaves as TCP-New Reno when the RTT of a flow is less than a certain reference RTT (e.g., 20ms). Otherwise, TCP-Hybla increases the congestion window size more aggressively to compensate throughput drop due to RTT increase.

TCP-Veno determines the congestion window size very similar to TCP-New Reno, but it uses the delay information of TCP-Vegas to differentiate non-congestion losses. When packet loss happens, if the queue size inferred by the delay increase is within a certain threshold, which is the strong indication of random loss, TCP-Veno reduces the congestion window by 20%, not by 50%.TCP-Illinois [4] uses a queuing delay to determine an increase factor α and multiplicative decrease factor β instantaneously during the window increment phase. Precisely, TCP-Illinois sets a large α and small β when the average delay d is small, which is the indication that congestion is not imminent, and sets a small α and large β when d is large because of imminent congestion. Similar to standard TCP, Illinois-TCP increases the congestion window by α and β, it is based on packet loss to define the congestion window value and the values of α and β are not constant using the delays.TCP Reno uses basic AIMD mechanism to adjust its congestion window size. It is the modified version of TCP Tahoe. These protocols are not scalable because additive increase is too slow and multiple decreases is too fast. Basic TCP uses packet loss to adjust the congestion window. It uses three duplicate acknowledgements to invoke Fast Retransmit and indicate segment lost. It retransmits the

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packet immediately and enters Fast Recovery. TCP Reno cannot detect multiple packet loss within the same window.TCP New Reno can be used to detect multiple losses within same window and does not exit fast recovery mode until all the data are acknowledged . Thus it does not reduce cwnd multiple times.FAST TCP uses packet loss and queuing delay as the congestion control parameter to adjust window after every Round Trip Time [5, 6].Yet Another High Speed TCP (YeAH-TCP) [7] starts with the Slow Start if cwnd < ssthresh and once cwnd reaches the ssthresh. It uses two modes, fast mode and slow mode. In fast mode, the congestion window increases aggressively .In slow mode, the protocol behaves similarly to Reno TCP. The mode is chosen according to the queue status, the minimal RTT (RTTbase) measured by the sender and the estimated RTT (RTTmin) from the current window.Compound TCP [8] is a Scalable and TCP-Friendly Congestion Control for High-speed Networks. It solves the compilation of two approaches delay based and loss based with the congestion avoidance of TCP protocol by a new variable delay window (dwnd) is added which gives more aggressive.

2.2 Important factors cause TCP performance degradation in Wireless Networks

Wireless Environment brings more challenges to TCP. We present some of the important factors that cause degradation in the performance of TCP in Wireless Networks.

Link Error Rate or High Bit Error Rate: Wireless hosts use radio transmission or infrared wave

transmission for communication. This lead to vulnerable to interference from the environment, signal attenuation, Doppler shift and multipath fading and loss of TCP data segments or acknowledgments, Hence, the TCP sender will unnecessary invoke congestion control and need Error control Mechanism at destination due to High Bit Error Rate on wireless links.

Bandwidth: Bandwidth is a insufficient resource in case of wireless networks. Bandwidth also

varies highly on wireless networks. The higher layers may be responsible and use different methods (e.g. compression) to take care of this problem

Node Mobility and Route Failures: Wireless hosts may move frequently while communicating.

During this movement the data sent to the wireless host is lost. TCP at the destination interprets this loss as congestion and unnecessary invokes congestion control mechanisms as when the move is complete the wireless host will start receiving data again. This causes the performance of TCP to degrade due to frequent recalculation of routes to the moving wireless host. It is possible that the existing route reestablishment and discovering a new route may take significantly longer than the RTO at the sender depends on the underlying routing protocol, mobility patterns of nodes, and traffic Characteristics. As a result, the TCP sender will unnecessary invoke congestion control and need Efficient Routing Protocol.

Multipath Routing: To minimize the frequency of route reestablishment, some routing protocols

maintain multiple routes between source and destination. Sometimes This results lead to significant number of out-of-sequence packets arriving at the receiver causing the generation of duplicate ACKs which cause the sender to invoke congestion control and need reassembling mechanism in order to data sent from sender.

Path Asymmetry: Several forms of Path Asymmetry are bandwidth asymmetry, loss rate

asymmetry, and route asymmetry, If the ACKs get bunched up, the sender may transmit data in a burst cause packet loss on the forward path and window growth and degrade performance to a fraction of the available bandwidth.

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Network Partition: If the sender and the receiver of a TCP connection lie in different partitions

due to node mobility or energy-constrained operation of nodes, all the sender's packets get dropped. The frequent disconnections cause a condition called serial timeouts at the TCP sender resulting in the sender invoking congestion control and lead to long idle periods during which the network is connected again.

TCP congestion window size: Routes are changed many times during the lifetime of a TCP

connection, the relationship between the congestion window size and the tolerable data rate becomes too loose. If the congestion window size is greater than an upper bound, the TCP performance will degrade. A specific network topology and flow patterns, TCP operates at an average window size that is much larger than optimal TCP’s window size resulting in increased packet loss due to the Contention on the wireless channel.

Power Limitation: Since each mobile node acts as router as well as an end system node that have

battery with limited power supply, invoke unnecessary retransmissions of TCP segments causing inefficient utilization of available power.

Interaction between MAC protocol and TCP: In a multi-hop environment, the interaction of the

802.11 MAC protocol with the TCP protocol mechanisms lead to unexpected serious Problems. These problems include. The main causes of these problems are instability, “link capture effect” one-hop unfairness, the hidden station and exposed station problems of the 802.11 MAC protocol.

2.3 TCP Performance improvement through detection of network states

Several approaches [9] have been proposed to improve TCP performance in Wireless Network. Many approaches depend on differentiating between the network states that cause packet losses and have the appropriate reaction in each case. They can be divided into three approaches are:

1. Network Feedback Approaches 2. Link Feedback Approaches 3. Transport Feedback Approaches

Transport end-to-end approaches are easier to implement and provide more flexibility. Network and Link feedback approaches are more accurate as the information is coming directly from the network. In this paper studies transport end-to-end approaches need no network support.

2.4 Wireless Loss Differentiating Algorithms

Loss Discrimination (LD) algorithm [10, 11, 12, 13, 14] used to estimate the cause of packet losses, to improve TCP performance over hetero

geneous wired-cum-wireless. The cause of packet loss can be found by using TCP state variable such as threshold, Round trip time, congestion window, inter arrival time, retransmission time out, Flight size and out of order. LD scheme is a Boolean function of the TCP state variable in the sender or receiver or proxy [15].

2.4.1 TCP Vegas Loss Predictor

To improve the performance TCP by differentiates congestion loss from wireless loss using Vegas Loss predictor (LP). It estimates the cause of packet loss on rate estimates and uses two parameter α and β. The actual transmission rate (AR) is cwnd/RTT and expected transmission rate is

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cwnd/RTTmin .The difference (diffv) =RTTmin*(ER-AR) .When diffv ≤ α, it is wireless loss. When diffv ≥ β, It is congestion loss. Hence, when α<diffv<β, the network state is the same as in the previous estimation [16].

2.4.2 Non congestion packet Loss Detection

Non congestion packet Loss Detection (NCPLD) uses load-throughput, delay and flight size to

estimate congestion status. If current Round Trip Time is greater than the estimated Round Trip Time, the network is congested. Else, packet loss is due to transmission error.

2.4.3 Spike scheme

The Spike scheme in sender or receiver side measures the current RTT, maximum (RTTmax) and minimum (RTTmin) Round Trip Time throughout the TCP session. Using these values, it computes two thresholds BspikeStart and BspikeEnd calculated as follows:

BspikeStart ← RTTmin + α (RTTmax − RTTmin) (1)

BspikeEnd ← RTTmin + β (RTTmax − RTTmin) (2)

If RTT > BspikeStart, loss due to congestion, Else if RTT < BspikeEnd, loss due to wireless loss, Else the network is in the previous state.

2.4.4 TCP New Reno with Loss Predictor

The TCP sender extends TCP New Reno with Loss Predictor in its error recovery scheme called TCP New Reno-LP. When packet random error rate is low and most of the packet losses due to congestion. Packet losses due to wireless loss when random error rate is high. This scheme achieves high good put in wireless link and fairness with concurrent TCP flows in network congestion. Ideal -LDA, Constant- LDA and Random –LDA can be used to assess the accuracy of the Loss Differentiation algorithms, establishing upper and lower bounds.

2.4.5 TCP Veno

TCP Veno [17] determines the backlog packets (N) in the buffer by Vegas’s mechanism. When the TCP sender receives 3DUPACK, Veno compares N with a threshold 3. If N < 3, it is a wireless losses and triggers wireless FR/FR.

2.4.6 Jitter-Based TCP (JTCP)

JTCP calculates a threshold (Jr), the average of the inter arrival jitter during one round-trip time. When the time receiving the 3DUPACK exceeds one RTT and Jr is larger than the inverse value of the current congestion window size, it is congestion loss else wireless loss and triggeres wireless FR/FR.

2.4.7 Robust End-To-End Loss Differentiation (RELDS)

A robust end-to-end loss differentiation scheme [18] is able to discriminate between congestion losses and wireless losses. This scheme estimates a moving threshold, a function of minimum sample RTT. When TCP sender receives 3DUPACK, if the moving threshold is not satisfied, wireless loss and triggers a wireless FR/FR.

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2.4.8 Improved TCP Friendly Rate Control (TFRC)

The improved TFRC [19] scheme utilizes one- way delay to regulate the transmission rate at the sender to differentiate between congestion losses and wireless link error losses for wired/wireless hybrid network

2.4.9 Detecting and Differentiating the Loss of Retransmitted Pack (DDLRP)

In [20], when the sender receives three dupacks, it retransmits the lost packet, calculates the

Loss_Detection_Point (RL Detection) to detect retransmission loss. TCP sender checks If the ACK packets for CW bit (RL differentiation) is set, network congested and reduces cwnd and enters fast recovery else transmission loss and retransmits the lost packet without reducing cwnd and enters fast recovery.

2.4.10 Loss Differentiation Algorithm based on Estimation of Queue Usage (LDA EQ)

End-to-End LDA EQ [21] in multi-hop wireless networks to estimate the rate of queue usage. If the estimated queue usage is smaller than a certain threshold when 3DUPACK is received, wireless losses and triggers wireless FR/FR. Whenever a wireless FR/FR is triggered, LDA is restoring TCP congestion control state to the previous state instead of reducing the transmission rate in the experiments of the work. That is because LDAs basically assume that TCP performance will be improved by not reducing the transmission rate.

Researchers are working on the enhancement of high speed congestion control protocols. Every year, one or two protocols are implemented but each one of them is having own specific strengths and weaknesses. Recently, the research work is interested in evaluating the performance of high speed TCP protocols by comparing 2 to 6 protocols [22, 23, 24, 25, 26, 27].

3. PROPOSED WORKS

3.1 TCP High Speed with Loss Discrimination

High Speed TCP [28] uses the value of the previous congestion window to compute its new congestion window value. High Speed TCP behaves like standard TCP when the congestion window (cwnd) is below a threshold. Above threshold High Speed TCP acts more aggressively in attaining bandwidth by increasing its congestion window size aggressively. On each arrival of a new acknowledgement, High Speed TCP increases its congestion window by the following:

cwnd = cwnd + α/ cwnd (3)

When congestion is detected through packet loss, the congestion window is decremented as follows:

cwnd = cwnd × (1-β) (4)

For congestion window values less than threshold, the values of α and β are 1 and 0.5 respectively, as with Standard TCP. When the congestion window is above the threshold, values of α and β are determined by a lookup table.

Pseudo-code for TCP High Speed-LD (Fast Retransmission) as follows: If (Received 3 DUPACK) or (Retransmission Time is expired)

IF (Actual Sending Rate > Flight Size) THEN

98 Wireless Loss cwnd ←ssthresh ELSE Congestion Loss ssthresh ← cwnd × (1-β) cwnd ← ssthresh

3.2 TCP Scalable with Loss Discrimation

Scalable TCP is an Additive Increase Multiplicative Decrease (AIMD) protocol, i.e. it increases its congestion window linearly and decreases it congestion window multiplicatively. Scalable TCP is similar to High Speed TCP, but it has fixed values for α and β. When a new acknowledgement is received, Scalable TCP increments the cwnd as follows:

cwnd = cwnd + 0.01 (5)

When congestion is detected, the congestion window is decremented as follows: cwnd = cwnd × 0.875 (6) Pseudo-code for TCP Scalable-LD (Fast Retransmission) as follows:

If (Received 3 DUPACK) or (Retransmission Time is expired) IF (Actual Sending Rate> Flight Size)

THEN Wireless Loss cwnd←ssthresh ELSE ssthresh ← cwnd × 0.875 cwnd ← ssthresh

3.3 TCP BIC with Loss Discrimination

BIC-TCP [29] makes an estimate of the available network bandwidth and sets a target window size, called maximum window. It maintains the current congestion window size in a variable called minimum window. BIC-TCP employs a binary search function to increment the minimum window to the midpoint of minimum window and maximum window when a new acknowledgement is received. But initially when the difference between the minimum window and the maximum window is large, BIC-TCP employs additive increase. When the difference is below a threshold value, BIC-TCP increments the congestion window size using binary search. Fast convergence, i.e. binary search increase combined with a multiplicative decrease, is used to converge quickly and achieve a fair share with other protocols.

Pseudo-code for TCP BIC-LD as follows:

If (Received 3 DUPACK) or (Retransmission Time is expired) IF (Actual Sending Rate > Flight Size)

THEN Wireless Loss cwnd←ssthresh ELSE Congestion Loss ssthresh ← cwnd =cwnd/ β cwnd ← ssthresh

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3.4 TCP CUBIC with Loss Discrimation

The main design goal of CUBIC [30] was to improve upon BIC-TCP by making it less aggressive. CUBIC uses the time delay between packet drops to adjust its congestion window value. As the name of this protocol represents, the window growth function of CUBIC is a cubic function, whose shape is very similar to the growth function of BIC. CUBIC is designed to simplify and enhance the window control of BIC. More specifically, the congestion window of CUBIC is determined by the following function

Wcubic=C (t-K) 3

+Wmax (7)

where C is a scaling factor, t is the elapsed time from the last window reduction, Wmax is the window size just before the last window reduction, and K = 3√Wmaxβ/ C, where β is a constant multiplication decrease factor applied for window reduction at the time of loss event .

Pseudo-code for TCP CUBIC-LD as follows:

If (Received 3 DUPACK) or (Retransmission Time is expired) IF (Actual Sending Rate >Flight Size)

THEN Wireless Loss cwnd←ssthresh ELSE Congestion Loss ssthresh ← β×Wmax cwnd ← ssthresh

3.5 TCP Newton Raphson Congestion Control with Loss Discrimination

TCP NRC-LD suggests two mechanisms to handle wireless losses modifying the congestion control mechanism of TCP NRC. To avoid the congestion control in bottle neck link, TCP NRC algorithm is used. To differentiate between the congestion and wireless loss, Loss Discrimination algorithm is used. To describe the algorithms that have been used in TCP the following terms are defined.

Segment: It is a TCP data or acknowledgement packet or both. Maximum Segment Size (Ms): It is

the size of the largest segment size that can be transmitted in TCP connection. The default of the Ms is 536 bytes. The TCP sender and receiver will send the desired Ms at the starting of connection.Receiver window (Rw): It is the advertised receiver window. It is a receiver side limit

on the amount of data. Congestion Window (Cw): It is the sender side limit on the amount of data

that the sender can transmit into the network and it may be reduced in response to congestion.Slow

Start Threshold (Sth): It is used to determine whether the slow start or congestion avoidance

algorithm is used to control data transmission. The Initial value of threshold may be the size of advertised window and it may be reduced in response to congestion.Flight Size (Fs): It is the

amount of data that can be sent but not yet acknowledgement.TCP NRC-LD algorithm has two mechanisms:

1. Newton Raphson Congestion Control 2. Packet Loss Detection and Discrimination

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3.5.1 Newton Raphson Congestion Control

NRC is used to control the congestion in bottleneck link by using following algorithms 1. Modified Slow Start

2. Modified Congestion Avoidance 3. Modified Fast Retransmission 4. Modified Fast Recovery

3.5.1.1 Modified Slow Start (MSS)

MSS is used to control the amount of sending data to the network. It is used at the beginning of transfer or after repairing loss detected by the retransmission timer. MSS is used if Cw<Sth. During MSS, a TCP sender increments Cw by 1*Ms for each acknowledgement which generated by receiver. Modified Slow Start ends when Cw≥Sth or when congestion is observed.

3.5.1.2 Modified Congestion Avoidance (MCA)

During Congestion Avoidance, the current Cw is incremented by eα in given eqn. (8) where α is window scaling factor determined by real root of algebraic equation which is found by Newton Raphson method for receiving every acknowledgement and it continues until congestion is detected.

Cw=Cw+eα; if no loss (8)

3.5.1.3 Modified Fast Retransmission (MFRT)

When an out of order segment arrives at the TCP receiver generates duplicate acknowledgement that is sent back to the sender to inform that a segment was lost and retransmit it. The duplicate acknowledgement can be caused by dropped segments or out of order. The TCP receiver will generate more timely information for a sender recovering from a loss through a retransmission timeout or Modified Fast Retransmit. TCP sender uses the MFRT to detect and repair loss based on incoming duplicate acknowledgement. After receiving 3 duplicate acknowledgements, reduce congestion window based on Packet Loss Discrimination algorithm.

3.5.1.4 Modified Fast Recovery (MFRC)

After MFRT sent missing segment, the MFRC algorithm transmit new data until a non-duplicate acknowledgement arise. The sender is in MFRC until a retransmission timeout occurs or an ACK arrives that acknowledges all of the data up to and including the data that was outstanding after it began

3.5.2 Modified Packet Loss Discrimation (MPLD)

MPLD algorithm is used to differentiate packet loss due to congestion from packet loss due to link noise. TCP sender uses the MFRT to detect and repair loss based on incoming duplicate acknowledgement. After receiving 3 duplicate acknowledgements, TCP sender computes and compares Actual sending rate and flight size. If the current actual sending rate is less than flight size, TCP sender assumes it as congestion loss and retransmits the packet using MRT with reducing congestion window by eβ based on given eqn.(9) where β is window scaling factor determined by real root of algebraic equation which is found by Newton Raphson method or double Ms and set up

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congestion window as slow start threshold plus 3 MTU and enters MFRC. Else, wireless loss and retransmits the packet using MFRT without reducing congestion window and enters MFRC.

Cw = Cw - eβ ; if loss (9)

Table 1. Pseudo-code for the proposed Newton Raphson Congestion Control with Loss

Discrimination Algorithm

4

.

SIMULATION

AND

PERFORMANCE

EVALUATION

4.1 Simulation Setup

A lot of experiments have been performed with any congestion in the network to study the performance of TCP by changing bandwidth and RTT of bottleneck link. It consists of six wired nodes, one router, one base station and six mobile nodes. First six wired nodes are connected with a router through 100MB (Mega Bytes) bandwidth and 10ms delay duplex wired connection. The router is connected with a base station through 10Mb and 100ms (milli seconds) delay duplex wired connection. Then seven mobile nodes and the base station are connected with a wireless duplex link .The sources (N0…N5) emits a number of flows towards corresponding destination (N8…N13) which traverses the bottleneck Router R and Base-station BS in between. Here the base-station which uses its adhoc routing protocol (DSDV) to route the packets to its correct destination. The traffic used File Transfer Protocol (FTP).

A lot of experiments on the above topology are carried to test the performance of High Speed TCP variants with the Enhanced NRC congestion control mechanism with Loss Discrimination and the results are compared with the previous high speed TCP variants such as BIC-TCP, CUBIC, High Speed TCP, Scalable TCP, NRC TCP and Enhanced High Speed TCP variants with Loss Discrimination such as TCP BIC-LD, TCP CUBIC-LD, TCP High Speed-LD, TCP Scalable-LD using NS-2.

INIT:

Cw←2*Ms Sth←Rw

IF (ACK is received and no loss) If (Cw<Sth):

Modified Slow Start Else

Modified Congestion Avoidance Cw=Cw+eα

IF (3 Duplicate ACKs are received) or (Retransmission Time is expired): Modified Fast Retransmission

Actual_Sending_Rate (Asr) ←Cw/RTT

Fs=Sending_Rate-(Receiving_ Rate+ Dropping_Rate ) If (Asr<Fs): Congestion loss Sth=Cw-eβ Cw=Sth Else: Wireless loss Cw=Sth Fast recovery

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4.2 TCP-Full Bandwidth Utilization

The flow of TCP NRC-LD is started with Existing High Speed TCP variants and Enhanced TCP high speed variants with Loss Discrimination. The experiments are run for 600ms and the congestion window for each flow is measured. Fig. 1 and Fig. 2 show the congestion window of TCP NRC-LD, TCP NRC and High Speed TCP-Variants flow, run separately and represented by the different color lines. The graph shows that the TCP NRC-LD is able to increment its congestion window very quickly so that it can attain the whole of available bandwidth by increasing the congestion window accordingly. The Enhanced TCP high speed variants with Loss Discrimination increment their congestion window than concerned existing High Speed TCP variants.

Figure 1. Tcp-Full Bandwidth Utilization (Compare Nrc, High Speed And Scalable)

Figure 2. TCP-Full Bandwidth Utilization (Comparison NRC, CUBIC and BIC) 4.3 TCP-Throughput

The average throughput for each flow is measured. Fig. 3 and Fig. 4 show the comparison of the accumulated throughput. It can be seen that the mean throughput of the existing algorithms is quantity low where as a better performance with TCP NRC-LD and the enhanced TCP high speed variants with Loss Discrimination. TCP NRC-LD gives an improvement in the value of mean throughout.

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Figure 3. Accumulated Throughputs (Compare NRC, High Speed and Scalable)

Figure 4. Accumulated Throughputs (Comparison NRC, CUBIC and BIC) 4.4 TCP-Packet Loss Rate

The Packet Loss Rate and Number of packets are sent for each flow is measured. Fig. 5 and Fig. 6 show the performance of six algorithms with congestion inserted and wireless loss link in the network. From this graph it is found that the performance with TCP NRC-LD algorithm is better and the enhanced high speed TCP variants with LD are better their PLR is zero, even if the number of packets sent is very high compared with BIC-TCP, CUBIC, High Speed TCP and Scalable TCP.

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Figure 6. TCP-Packet Loss Rate (Comparison NRC, CUBIC and BIC) 4.5 TCP- Fairness

This fairness [31] issue has been discussed and evaluated that packet size can affect the packet drop rate experienced by a flow. The average throughput for each flow is measured between the interval [200, 600] ms. The results obtained are compared to the earlier results. In Fig. 7 and Fig. 8 show that the experiment in which the Enhanced TCP NRC-LD is much fair in sharing the bandwidth than TCP NRC and Enhanced High Speed TCP variants with LD are fair in sharing compared to previous High Speed TCP Variants.

Figure 7. TCP- Fairness (Compare NRC, High Speed and Scalable)

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5.

CONCLUSIONS

We enhanced TCP NRC with Loss Discrimination and previous High Speed TCP with Loss Discrimination mechanism by modification congestion control mechanism in TCP Sender. A detailed evaluation of TCP NRC-LD and TCP NRC with previous high speed TCP variants has been developed using NS2 simulator. The outcome of the study shows that TCP NRC-LD is able to increment its congestion window rapidly when compared to previous high speed TCP variants. The mean throughput of TCP NRC-LD has improved. When compared to PLR, the present algorithm TCP NRC-LD performs better. The fairness has been improved when TCP NRC-LD algorithm is being improved. The above comparison shows that the present study based on TCP NRC-LD performs better than TCP NRC and the previous high speed congestion control mechanism such as BIC-TCP, CUBIC, HS-TCP, and Scalable-TCP. The Enhanced High Speed TCP variants with LD provide better performance than their previous High Speed TCP variants.

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