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. JOURNAL OF COMPUTING, VOLUME 4, ISSUE 5, MAY 2012, ISSN 2151-9617 https://sites.google.com/site/journalofcomputing WWW.JOURNALOFCOMPUTING.ORG 213 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].