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_0: We consider an IEEE 802.11 based wireless LAN where an access point is used to connect a fixed number of users to the Web or to a shared file system. Users alternate between activity periods (corresponding to the download of a file) and idle periods (corresponding to think times). We first consider the interaction of TCP with the IEEE 802.11 MAC protocol, and get approximate expressions for the TCP throughput in the presence of n"c competing persistent connections. This result is then used to develop a queueing model, which provides the mean session delay in the presence of short-lived flows. The analysis also accounts for the TCP delayed ACK option. Comparison with simulation outcomes is provided, validating the model and providing guidelines for network designers. A particular emphasis is devoted to the impact of the TCP's advertised window size; in particular, it is proved that setting it to a small value leads to insensitivity of mean file transfer times to the file size distribution.
@cite_16: Today, IEEE 802.11 wireless LAN (WLAN) is a prevailing solution for the wireless Internet access while transport control protocol (TCP) is the dominant transport protocol in the Internet. It is known that, in the infrastructure WLAN with multiple long-lived TCP flow stations, the actual number of contending TCP stations is limited to a small number, and the aggregated TCP throughput is basically independent of the total number of TCP stations. It is due to the behavior of the TCP flow control in the infrastructure WLAN, where the downlink (i.e., access point-to-stations) is the bottleneck link. In this paper, we develop an accurate and realistic analytical model of long-lived TCP over WLAN based on a well-known p-persistent model of the 802.11. We calculate the average number of the active TCP stations as well as the aggregated TCP throughput using our model for a given number of TCP stations and the maximum TCP receive window size. We verify our model via ns-2 simulations. Moreover, we find from our work that the minimum contention window sizes of the standards (i.e., 31 and 15 for IEEE 802.11b and 802.11a, respectively) are not optimal in the sense of the TCP throughput maximization
@cite_11: In wireless LANs (WLANs), the medium access control (MAC) protocol is the main element that determines the efficiency in sharing the limited communication bandwidth of the wireless channel. In this paper we focus on the efficiency of the IEEE 802.11 standard for WLANs. Specifically, we analytically derive the average size of the contention window that maximizes the throughput, hereafter theoretical throughput limit, and we show that: 1) depending on the network configuration, the standard can operate very far from the theoretical throughput limit; and 2) an appropriate tuning of the backoff algorithm can drive the IEEE 802.11 protocol close to the theoretical throughput limit. Hence we propose a distributed algorithm that enables each station to tune its backoff algorithm at run-time. The performances of the IEEE 802.11 protocol, enhanced with our algorithm, are extensively investigated by simulation. Specifically, we investigate the sensitiveness of our algorithm to some network configuration parameters (number of active stations, presence of hidden terminals). Our results indicate that the capacity of the enhanced protocol is very close to the theoretical upper bound in all the configurations analyzed.
@cite_16 provides an analysis for a given number of STAs and maximum TCP receive window size by using the well known @math persistent model proposed in @cite_11 . However both @cite_16 and @cite_11 do not consider the effect of RTT on the performance. In @cite_0 , a queueing model is proposed to compute the mean session delay of HTTP sessions in the presence of short-lived TCP flows and the impact of TCP maximum congestion window size on this delay is studied.