In a multirate WLAN with a single access point (AP) and several stations (STAs), we obtain analytical expressions for TCP-controlled long file transfer throughputs allowing nonzero propagation delays between the file server and STAs. We extend our earlier work in [3] to obtain AP and STA throughputs in a multirate WLAN, and use these in a closed BCMP queueing network model to obtain TCP throughputs. Simulation show that our approach is able to predict observed throughputs with a high degree of accuracy.
@cite_4: 
@cite_8: There is a vast literature on the performance modeling of the 802.11 MAC protocol, but the interplay between the TCP dynamics and the self-regulating behavior of the 802.11 CSMA CA access method has not been sufficiently investigated. In addition, it has been observed that TCP stations in a WLAN are sporadically active due to the TCP flow control mechanisms. This makes traditional saturated models of the network capacity of 802.11 WLANs not very accurate. We presented a rigorous analytical model to calculate the distribution of the number of active TCP stations in a WLAN with multiple long-lived TCP flows [R. Bruno, M. Conti, E. Gregori, Performance modelling and measurements of TCP transfer throughput in 802.11-based WLAN, in: Proceedings of the IEEE MsWiM 2006, Torremolinos, Malaga, Spain, 2006, pp. 4-11, [1]]. Starting from this analysis, in this paper we derive a simple but accurate closed-form expression of the per-connection TCP throughout as a function of the average duration of collisions, the average backoff period and the TCP packet size. We validate this formula through performance tests carried out on a real WLAN. Then, we use our model to mathematically study the optimal minimum contention window size to maximize the TCP throughput. Our analytical results indicate that the initial window size specified in the 802.11b standard is about two times larger than the optimal one. However, we also show that the TCP throughput performance is not very sensitive to changes of the minimum contention window size, and that the TCP flows significantly underutilize the channel bandwidth also in the optimal MAC operating state.
@cite_10: We consider several WLAN stations associated at rates r"1,r"2,...,r"k with an Access Point. Each station (STA) is downloading a long file from a local server, located on the LAN to which the Access Point (AP) is attached, using TCP. We assume that a TCP ACK will be produced after the reception of d packets at an STA. We model these simultaneous TCP-controlled transfers using a semi-Markov process. Our analytical approach leads to a procedure to compute aggregate download, as well as per-STA throughputs, numerically, and the results match simulations very well.
@cite_9: In this letter we develop an average-value analysis of the TCP performance in 802.11 WLANs. Our model characterizes the equilibrium conditions of the network, and this method yields a simple, yet precise, estimate of the throughput obtained by persistent TCP flows. Via simulations we study the accuracy of the model predictions.
@cite_1: Performance analysis of TCP-controlled long file transfers in a WLAN in infrastructure mode is available in the literature with one of the main assumptions being equal window size for all TCP connections. In this paper, we extend the analysis to TCP-controlled long file uploads and downloads with different TCP windows. Our approach is based on the semi- Markov process considered in [1] and [2], but with arbitrary window sizes. We present simulation results to show the accuracy of the analytical model.
@cite_3: We provide analytical models for capacity evaluation of an infrastructure IEEE 802.11 based network carrying TCP controlled file downloads or full-duplex packet telephone calls. In each case the analytical models utilize the attempt probabilities from a well known fixed-point based saturation analysis. For TCP controlled file downloads, following (In Networking '04, LNCS 2042, pp.?626---637), we model the number of wireless stations (STAs) with ACKs as a Markov renewal process embedded at packet success instants. In our work, analysis of the evolution between the embedded instants is done by using saturation analysis to provide state dependent attempt probabilities. We show that in spite of its simplicity, our model works well, by comparing various simulated quantities, such as collision probability, with values predicted from our model. Next we consider N constant bit rate VoIP calls terminating at N STAs. We model the number of STAs that have an up-link voice packet as a Markov renewal process embedded at so called channel slot boundaries. Analysis of the evolution over a channel slot is done using saturation analysis as before. We find that again the AP is the bottleneck, and the system can support (in the sense of a bound on the probability of delay exceeding a given value) a number of calls less than that at which the arrival rate into the AP exceeds the average service rate applied to the AP. Finally, we extend the analytical model for VoIP calls to determine the call capacity of an 802.11b WLAN in a situation where VoIP calls originate from two different types of coders. We consider N 1 calls originating from Type 1 codecs and N 2 calls originating from Type 2 codecs. For G711 and G729 voice coders, we show that the analytical model again provides accurate results in comparison with simulations.
@cite_2: The network scenario is that of an infrastructure IEEE 802.11 WLAN with a single AP with which several stations (STAs) are associated. The AP has a finite size buffer for storing packets. In this scenario, we consider TCP-controlled upload and download file transfers between the STAs and a server on the wireline LAN (e.g., 100Mbps Ethernet) to which the AP is connected. In such a situation, it is well known that because of packet losses due to finite buffers at the AP, upload file transfers obtain larger throughputs than download transfers. We provide an analytical model for estimating the upload and download throughputs as a function of the buffer size at the AP. We provide models for the undelayed and delayed ACK cases for a TCP that performs loss recovery only by timeout, and also for TCP Reno. The models are validated in comparison with NS2 simulations.
@cite_13: Throughput analysis of bulk TCP downloads in cases where all WLAN stations are associated at the same rate with the AP is available in the literature. In this paper,we extend the analysis to TCP uploads for the case of multirate associations. The approach is based on a two-dimensional semi- Markov model for the number of backlogged stations. Analytical results are in excellent agreement with simulations performed using QUALNET 4.5.
@cite_12: There is a vast literature on the throughput analysis of the IEEE 802.11 media access control (MAC) protocol. However, very little has been done on investigating the interplay between the collision avoidance mechanisms of the 802.11 MAC protocol and the dynamics of upper layer transport protocols. In this paper, we tackle this issue from an analytical, simulative, and experimental perspective. Specifically, we develop Markov chain models to compute the distribution of the number of active stations in an 802.11 wireless local area network (WLAN) when long-lived transmission control protocol (TCP) connections compete with finite-load user datagram protocol (UDP) flows. By embedding these distributions in the MAC protocol modeling, we derive approximate but accurate expressions of the TCP and UDP throughput. We validate the model accuracy through performance tests carried out in a real WLAN for a wide range of configurations. Our analytical model and the supporting experimental outcomes show that 1) the total TCP throughput is basically independent of the number of open TCP connections and the aggregate TCP traffic can be equivalently modeled as two saturated flows; and 2) in the saturated regime, n UDP flows obtain about n times the aggregate throughput achieved by the TCP flows, which is independent of the overall number of persistent TCP connections.
@cite_3 and @cite_4 provide a model for single rate AP-STA WLAN assuming zero RTT and consider file transfers from a server located in the LAN. An extension of this model in @cite_13 considers two rates of association with long file uploads from STAs to a local server. The multirate case, with @math rates, is analysed in @cite_10 . @cite_1 considers the single rate case, but allows simultaneous TCP uploads and downloads with arbitrary maximum window sizes. @cite_12 and @cite_8 analyze TCP-controlled uploads and downloads in the presence of UDP traffic. However, the effect of RTT on the network performance is ignored. The letter @cite_9 gives the average value analysis of TCP performance with upload and download traffic without considering RTT. In @cite_2 , finite buffer AP with TCP traffic in both upload and download direction is analysed with delayed and undelayed ACK cases. They consider server system located on the Ethernet to which the AP is connected and hence number of packets in flight'' outside the WLAN is ignored.