Experimented Goodput Measurement of Standard TCP Versions Over Large-Bandwidth Low-Latency Bottleneck

JOURNAL OF COMPUTING, VOLUME 4, ISSUE 5, MAY 2012, ISSN 2151-9617 https://sites.google.com/site/journalofcomputing WWW.JOURNALOFCOMPUTING.ORG 212 Experimented Goodput Measurement of Standard TCP Versions over Large-Bandwidth Low-Latency Bottleneck

Ghassan A. Abed, Mahamod Ismail, and Kasmiran Jumari

Abstract—Goodput of Transmission Control Protocol (TCP) is the number of useful data bits, transferred by the network elements to a certain destinations, per unit of time. In communications networks, network layer, transport layer, and occasionally data link layer protocol overhead is involved in the throughput, but is excluded from the goodput. Goodput is constantly lesser than the throughput where the throughput means the gross bits rate which is physically transmitted, that mostly is lesser than network access connections rapidity (the link bandwidth or the link capacity). In other side, TCP flow control, congestion avoidance, and slow-start may possibly cause a poorer goodput than the maximum throughput. This article provide an experimented results to the goodput measurement for six TCP source variants, Tahoe, Reno, Newreno, Sack, Fack, and Vegas. The goodput analysis based on using a specific network topology with large-bandwidth and low-latency bottleneck using Network Simulator 2 (NS-2). The obtained results showed the huge differences among the measured goodput for these TCP’s.

Index Terms— Goodput, TCP, NS-2, MSS. —————————— ——————————

1 INTRODUCTION OODPUT is defined as the sum of single packets In the last years, computer networks and mobile cellu- delivered to a finale host in a given time period, as G lar systems have qualified incredible evolution and a lot opposed to the overall number of packets trans- of computers and other user equipment’s become linked ferred in a given time period that includes the retransmit- together with most mutual protocol stack used being TCP. ted packets. The rationale behind measuring the goodput Currently, it is hard to recognize the congestion control is that the end operators of TCP flow are concerned with mechanisms that are applied by different engines in In- transferring single packets and do not care about the ternet. The header of TCP does not deliver any facts for number of retransmissions cycles executed by the TCP them. One more imperative problem is the manner that source [1]. Let's say, if a file is transmitted, the goodput these mechanisms are employed in diverse operating sys- that the operator experiences correspond to the size of file tems [4]. The greatest universal transport protocol in- in bits divided by the file transferring period of time. volved is the TCP and in the original accomplishment of Through the previous two decades, several of mecha- TCP, a very small number of variants were done to mini- nisms were proposed to enhance the standard TCP ver- malize the congestion in network path. Employment used sions, Tahoe and Reno. Afterward Jacobson [2] introduced accumulative confident acknowledgements and the expi- the his algorithm of congestion control, then TCP devel- ration of a retransmission timer to afford reliability based opment grow into actual dynamic and many algorithms on a modest go-back-n model. Some successive variants have been assumed for congestion control to enhancing of TCP grounded on the mechanisms of congestion con- the stability, and bandwidth sharing among flows over trol and avoidance have been proposed and established wired and wireless networks. Actually, currently TCP is [5]. The object beyond the differences of TCP is that every not fit appropriate for wireless networks due to losses variant takes certain singular principles. The prime TCP resulted from using radio channels and the problems are has been called by TCP Tahoe. While TCP Reno comple- misread as indication of congestion by recent TCP struc- ments new technique to improve congestion control of tures and leading to an unnecessary decreasing of the Tahoe, this mechanism called fast recovery. The newest transmission rate. Therefore, TCP needs additional con- retransmission algorithm was added to Reno to get new nection layer protocols like using split connections or reli- TCP termed as Newreno. Fack TCP is a Reno but uses able link layer approach to professionally work in wire- forward acknowledgment technique. The usage of Sacks less links [3]. allows to the receiver to indicate some extra segment that ———————————————— received with non-order during single duplicate ACK, • Ghassan A. Abed is PhD candidate in Department of Electrical, Elec- while TCP Vegas assumes its individual exclusive ap- tronic, and Systems Engineering Faculty of Engineering and Built Envi- proaches for congestion control [6]. ronment, National University of Malaysia, UKM. • Prof. Dr. Mahamod Ismail is with Faculty of Engineering and Built Envi- ronment, National University of Malaysia, UKM. • Prof. Dr. Kasmiran Jumari is with Faculty of Engineering and Built Envi- ronment, National University of Malaysia, UKM.

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TCP congestion control algorithms are the leading ob- If the congestion window has constant value, the ACK ject to using the networks applications successfully in timing of the sent packets will depend on the ACK of the spite of source bottlenecks and mostly impulsive the ac- first set of packets (early packets). TCP sliding window cess patterns of users. TCP Reno, Sack, Tahoe, Newreno, depend on ACK clock which calculate the sender flow Fack and Vegas, are represent the source TCP variants rate and when RTT changed with different values, the and each variants support different congestion control sliding window will determine the mean sending rate of algorithm. The base of TCP congestion control is complete window per average RTT. The transmission grounded on Additive Increase Multiple Decrease window size controlled by dependence on the ACKs re- (AIMD) algorithm, by halving the window size when ceived each RTT and these parameters indicate the gen- congestion window having a loss in packet, and growing eral differences between TCP versions. The main function the window in one segment for every Round Trip Time of TCP window control is to obtain high packets rate with (RTT). minimum losses by avoiding network overloading in the same time to provide optimum sharing to the network The second module of congestion control is the re- bandwidth among connections. The optimum bandwidth transmission timer, containing the exponential bake-offs sharing can changed because the varying amounts of of the retransmit timer if the packet that retransmitted is overcrowding between traffics over the network, also it dropped. The third essential module is the slow-start because the varying in network itself like the updates in mechanism for the primary exploratory for existing routing or the time-varying capacity over radio links [9]. bandwidth. TCP Tahoe and TCP Reno are mostly applied over The other congestion control mechanism is the clock- many wireless applications because of the effective con- ing of ACK. Everywhere the acknowledgments arrived to gestion control mechanisms. These mechanisms provide the sender is used to clock-out the transmission for the varying in size of congestion window depending on ACK new next packet. The TCP source variants discussed here, status, thus when packets acknowledged the window size where all share the many features like slow-start, except is increased and decreased when detect lost in packets. In TCP Vegas, and all follow to the fundamental basis of TCP Tahoe, Reno, and Vegas, the congestion avoidance slow-start, AIMD, retransmit timers, and clocking of phase algorithm permit to the window size to increase by ACK. one segment every RTT. This increment stop when the window size reaches the congestion point and that will stimulates the window size to decrease and slow-down to 2 TCP VARIANTS BACKGROUND the next phase.

There are many TCP variants that modified and devel- Basically, TCP seeks to provide reliability to data oped with respectively with the communications needs. transmitted between two hosts. TCP is trying to provide Most of TCP current versions are include set of algo- reliable data transmission between two entities. TCP ap- rithms which built to control the congestion in critical plies set of rules to handle lost in packets resulted from links of network with maintaining the network through- physical errors in transmission or because of the conges- put [7]. In present years, TCP has been faced the fast tion in cross traffics [4]. In recent days, the need to pro- growth in internet in parallel with the demand increasing vide reliable data transmission over Internet traffics or to transfer the media on high speed links supported TCP. cellular mobile systems becomes very important. TCP In order to improve its performance TCP cuts down the represents the prevailing protocol that provide reliability size of its congestion window resulted in further per- to data transferring in all end-to-end data stream services formance degradation. This is a more serious problem in on the Internet and many of new networks. Usually, it’s bursty and highly mobile networks which have rapid not easy to determine the available bandwidth for TCP topological changes [8]. TCP provides division for se- packets flow. In fact, it’s very complex problem due to the quenced data stream into packets, confirms the packets effects of the congestion control of TCP and the network delivery with the possibility of losing the IP layer loses, dynamics. These two factors make the proceedings of retransmit, reorders, or packets duplication, and monitor- exact allocation for the packets flow complicated. The ing the network band capacity to avoiding congestions. approved mechanism to detect the optimum bandwidth TCP protocol can provide over two end points connec- to send packets from TCP sender is congestion control tion, flow rate controlling with bidirectional link and data [10]. The understood of TCP behavior and the approaches reliability [9].In addition, each TCP sender can regulates to enhance the performance of TCP in wireless channels the size of the congestion window using the congestion have been many difficulties and challenges. In parallel control mechanism and the TCP can update and dynami- with this, considerable researches dealt with in detail cally regulate the window size depending on the packets many proposed development and mechanisms to raise ACK or by indicates the packets losses when occur. the efficiency of the performance of TCP, some of these problems already solved, but others are still open [11].

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The object behind the differences of TCP is that each TABLE 1 type has some distinct criteria such as the base TCP has SIMULATION PARAMETERS become known as TCP Tahoe. TCP Reno adds one new mechanism called fast recovery to TCP Tahoe. Newreno Parameter Value uses the newest retransmission mechanism of TCP Reno. Number of Source nodes 4 The use of Sacks permits the receiver to specify several Number of Source nodes 4 additional data packets that have been received out of Number of Routers 2 order within one dupack. TCP Vegas proposes its own Bandwidth of Bottleneck (R1- 100 Mbps unique retransmission and congestion control strategies. R2) TCP Fack is Reno TCP with forward acknowledgment Propagation delay of all links 3 msec [12]. Bandwidth of Source Nodes 10 Mbps (S - R1) Bandwidth of Destination 10 Mbps 3 NETWORK TOPOLOGY AND SIMULATION Nodes (D - R1) PARAMETERS Packet size 536,1460 Bytes As mentioned before, the experiments performed using Max. window size 128 packets NS-2 simulator [13] and grounded on using Tcl script. The Queue scheme Drop-Tail proposed topology included four source nodes linked to tcpTick 0.5sec corresponding four nodes as destination nodes through Queue size 64 packets two routers with single bottleneck. The propagation delay Simulation time 11sec of all topology links set to 3 msec while the bandwidth of TCP protocol Tahoe, Reno, Ne- the source and destination nodes set to 10 Mbps except wreno, Vegas, Sack, the bottleneck which is set to 100 Mbps as shown in Fig.1 and Fack where that achieved the large-bandwidth concept.

In fact, the large-bandwidth low-latency bottleneck repre- The nodes groups S and D are represented the TCP send- sents the main link in next generation network such as er and receiver respectively, and the queue size between Long Term Evolution (LTE) networks, where the goodput them is set to 64 packets while the queuing type is chose of standard TCP’s can give a premium evaluation to the to be DropTail. In other hand, the maximum bound of performance of these variants over next generation net- TCP window size is set to 128 packets and tcpTick to 0.5 works. The simulation and links parameters are briefed in second where tcpTick is the timer clock granularity for Table 1. measuring RTT intervals (the default value 0.1 sec).

Fig. 1. Proposed Network Topology for Goodput Measurements

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The general concept of TCP Goodput, that it’s measure the total of TCP payload bytes per second that the system under test can transmit and receive between its ports and the Maximum Segment Size (MSS). Therefore, the maximum segment size effect on the goodput behaviour, that's why, the experiment separately, used two segment sizes, 536 Bytes and 1460 Bytes to achieve high accuracy to the estimated goodput. At last, the simulation duration is fixed to 11sec for each experiment (when MSS= 536 Bytes and when MSS=1460 Bytes).

4 RESULTS AND DISCUSSION As explained previously, the goodput measurement based on two trials, the first when MSS equal to 536 Bytes and the Fig. 2. Demonstration of Different TCP’s Goodput Measurements second when it 1460 Bytes and each experiment test the (MSS=536 Bytes). goodput for Tahoe, Reno, Newreno, Sack, Fack, and Vegas. That because the tests script measures the goodput for each MSS value separately and the MSS changed for each experiment.

The full results of the goodput measuring over the proposed topology for TCP source variants are shown in Table 2 and Table 3 while the results are demonstrated in the column chart in Fig. 2 and Fig. 3.

TABLE 2 RESULTS OF DIFFERENT TCP’S GOODPUT MMS=536 BYTES

TCP Goodput (Mbps) Tahoe 18.220 Reno 21.936 Fig. 3. Demonstration of Different TCP’s Goodput Measurements Newreno 25.044 (MSS=1460 Bytes). Vegas 8.640 Sack 22.110 Fack 1.369 From these results, Fack TCP provides poorer goodput in both trials, in spite of the goodput for Fack TCP improved when MSS=1460 Bytes, this due to the slow congestion control mechanism used with Fack where it cannot covering the packet losing and after each loss, the congestion window TABLE 3 initiated from the initial value and increase the window RESULTS OF DIFFERENT TCP’S GOODPUT again. In other side, Newreno perform better than other TCP MMS=1460 BYTES variants where that because the intelligent congestion control mechanism used in Newreno, where the combination of four phases, slow-start, congestion avoidance, fast recovery, TCP Goodput (Mbps) and fast retransmit assist Newreno to covering the packet Tahoe 18.220 dropping. In addition, after packet loss, the congestion con- Reno 21.936 trol start form the half window size and no need to start Newreno 25.044 from the initial window level where all this features assisted Vegas 8.640 Newreno to give high goodput. Reno showed a reasonable Sack 22.110 goodput compared with other variants but the degradation Fack 1.369 in Reno goodput is because Reno cannot perform well with high packet loss rate, where this situation expected in our simulation.

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Tahoe and Sack (Sack is improved Reno version) per- [7] G. A. Abed, M. Ismail, and K. Jumari., "ARCHITECTURE AND formed a critical goodput, where Sack used the features of FUNCTIONAL STRUCTURE OF TRANSMISSION CONTROL PRO- Reno to cover the expected packet loss while Tahoe limitedly TOCOL OVER VARIOUS NETWORKS APPLICATIONS," Journal of covered the packet loss due to Tahoe used fast recovery but Theoretical and Applied Information Technology, vol. 34, 2011. the fast retransmit not included in the congestion control [8] S. Henna, "A Throughput Analysis of TCP Variants in Mobile Wireless mechanism. In Vegas, and because it used a special conges- Networks," 2009, pp. 279-284. tion control approach, Vegas can give high throughput but [9] N. Möller, Automatic control in TCP over wireless: School of Electrical cannot give a reasonable goodput. This due to the conges- Engineering, Royal Institute of Technology, 2005. tion control of Vegas estimate the congestion point according [10] H. Abrahamsson, O. Hagsand and I. Marsh, "TCP over high speed to the current and expected window size, so the packet loss variable capacity links: A simulation study for bandwidth allocation," become lesser than other TCP variants but the goodput ro- 2002, pp. 117-129. mans poor as shown in graphical demonstration of the ex- [11] X. Chen, H. Zhai, J. Wang and Y. Fang, "A survey on improving TCP perimented results with two trials, one when MSS=536 Bytes performance over wireless networks," Resource management in wire- and the other when MSS=1460 Bytes. less networking, pp. 657-695, 2005. [12] G. A. Abed, M. Ismail, and K. Jumari, "Behavior of cwnd for TCP source variants over parameters of LTE networks," Information Technology 5 CONCLUSION Journal, vol. 10. This paper provided and experimented results to the [13] N. Simulator, "ns-2," 1989. goodput for six TCP source variants over large- bandwidth and low-latency bottleneck of 100 Mbps and 3 msec as a bandwidth and propagation delay. The TCP Ghassan A. Abed received his B.Sc. and M.Sc. degree in Computer Engineering from variants showed a large goodput difference in number of University of Technology, Baghdad, Iraq, in Mbps transferred over the bottleneck in spite that all of 1996 and 2003 respectively. He was Head of them used the same parameters and conditions. Two tri- Transmitters and Receivers Dept. in als used in the test, one when MSS=536 Bytes and the Microwave Research Centre in Ministry of Sciences and Technology, Iraq. Currently, he other when MSS=1460 Bytes, where the two segment size is PhD candidate in National University of achieve more reality and credibility to the goodput per- Malaysia (UKM), Selangor, Malaysia. He is formance. Newreno gave the best goodput compared working in Mobile and Computer Wireless with other versions while Fack gave the lesser goodput. Networks and his research interests include developing new TCP mechanisms to improve performance of TCP over 4G systems and In fact, the all TCP versions used in the experiments can- beyond. not achieve the high level requirements of the next generation networks, especially when an wireless channels and nodes includes in the networks such as the cellular Prof. Dr.Mahamod Ismail joined the Depart- ment of Electrical, Electronics and System En- system. For this reasons, and from the obtained results, gineering, Faculty of Engineering and Built the congestion control of all standard TCP variants are Environment, Universiti Kebangsaan Malaysia require to improve to be able to provide an end-to-end (UKM) in 1985 and currently he is a Professor reliable connection with lesser packet loss and high in Communication Engineering. He received the B.Sc. degree in Electrical and Electronics from goodput level. University of Strathclyde, U.K. in 1985, the M.Sc. degree in Communication Engineering ACKNOWLEDGMENT and Digital Electronics from University of Manchester Institute of Science and Technology (UMIST), Manchester U.K. in 1987, and the This study is sponsored by Universiti Kebangsaan Malay- Ph.D. from University of Bradford, U.K. in 1996. He was with the first sia (UKM) through the university research grant OUP- Malaysia Microsatellite TiungSat Team Engineers in Surrey Satellite Technology Ltd. U.K. for 9 months started in June 1997. His re- 2012-182. search interests include mobile and satellite communication, and wireless networking particularly on the radio resource management REFERENCES for the next generation wireless communication network. He is currently the Chair of IEEE Malaysia Section. [1] S. Sharma, D. Gillies, and W. Feng, "On the Goodput of TCP NewReno in Mobile Networks," 2010, pp. 1-8. [2] V. Jacobson, "Congestion avoidance and control," 1988, pp. 314-329. Prof. Dr.Kasmiran Jumari received his B.Sc. from National University Malaysia, 1976 and

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