Average-Value Analysis of 802.11 WLANs with Persistent TCP flows

The widespread use of the IEEE 802.11 MAC as a layer-2 protocol for wireless local area networks has generated an extensive literature on its performance modeling. However, most of the available studies evaluate the capacity of WLANs in saturated conditions, while very little has been done on investigating the interactions between the 802.11 MAC protocol and the various transport protocols that are used to deliver users\u27 traffic. Recently there have been renewed efforts to understand and model the TCP dynamics in 802.11 WLANs. In general, these models employ multi-dimensional discrete-time Markov chains to analyze the distributions of the number of TCP packets enqueued in the stations\u27 buffers. Then, they exploit those distributions to derive both the average number of active TCP stations and the aggregate TCP throughput. However, this approach may rapidly lead to the explosion of the model state-space when the number of TCP flows is large. In this technical report we propose a novel modeling approach by developing an average-value analysis of TCP performance in 802.11 WLANs. Our model intuitively characterizes the equilibrium conditions for the network, and this method yields a precise estimate of the throughput of persistent TCP flows. Extensive simulations validate the accuracy of our analysis

Stochastic Models of TCP Flows over 802 11 WLANs

This technical report develops an analytical framework to model the interaction between TCP and 802:11 MAC protocol over a WLAN, when concurrent TCP downlink and uplink connections are active. Assuming a TCP advertised window equal to one, we formulate a Markov model to characterize the dynamic network contention level, de ned as the expected number of wireless stations having at least a frame to transmit. Exploiting the stochastic characterization of the dynamic contention level induced by the TCP ow control, we develop an accurate model of the MAC protocol behavior to evaluate the TCP throughput performance. Comparison with simulation results validates the model, which provides the analytical basis for the optimization of the system performance. In particular, we prove that using a TCP advertised window equal to one ensures a fair access to the TCP ows of the channel bandwidth, irrespective of the number of TCP downlink or uplink connections. Moreover, we show that the aggregate TCP throughput is almost independent of the number of wireless stations in the network

Cross-layer Loss Differentiation Algorithm to Improve TCP Performances in WLANs

International audienceLoss Differentiation Algorithms (LDA) are currently used to determine the cause of packet losses with an aim of improving TCP performance over wireless networks. In this work, we propose a cross-layer solution based on two LDA in order to classify the loss origin on an 802.11 link and then to react consequently. The first LDA scheme, acting at the MAC layer, allows differentiating losses due to signal failure caused by displacement or by noise from other loss types. Moreover, in case of signal failure, it adapts the behavior of the MAC layer to avoid a costly end-to-end TCP resolution. The objective of the second LDA scheme, which acts at the TCP layer, is to distinguish a loss due to interferences from those due to congestions and to adapt consequently the TCP behavior. The efficiency of each LDA scheme and of the whole cross-layer solution are then demonstrated through simulations

Performance Modelling and Measurements of TCP Transfer Throughput in 802.11based WLANs

The growing popularity of the 802.11 standard for building local wireless networks has generated an extensive literature on the performance modelling of its MAC protocol. However, most of the available studies focus on the throughput analysis in saturation conditions, while very little has been done on investigating the interactions between the 802.11 MAC protocol and closed-loop transport protocols such as TCP. This paper addresses this issue by developing an analytical model to compute the stationary probability distribution of the number of backlogged nodes in a WLAN in the presence of persistent TCP-controlled download and upload data transfers. By embedding the network backlog distribution in the MAC protocol modelling, we can precisely estimate the throughput performance of TCP connections. A large set of experiments conducted in a real network validates the model correctness for a wide range of configurations. A particular emphasis is devoted to investigate and explain the TCP fairness characteristics. Our analytical model and the supporting experimental outcomes demonstrate that using default settings for the capacity of devices\u27 output queues provides a fair allocation of channel bandwidth to the TCP connections, independently of the number of downstream and upstream flows. Furthermore, we show that the TCP total throughput does not degrade by increasing the number of wireless stations

VoIP Call Admission Control in WLANs in Presence of Elastic Traffic

VoIP service over WLAN networks is a promising alternative to provide mobile voice communications. However, several performance problems appear due to i) heavy protocol overheads, ii) unfairness and asymmetry between the uplink and downlink flows, and iii) the coexistence with other traffic flows. This paper addresses the performance of VoIP communications with simultaneous presence of bidirectional TCP traffic, and shows how the presence of elastic flows drastically reduces the capacity of the system. To solve this limitation a simple solution is proposed using an adaptive Admission and Rate Control algorithm which tunes the BEB (Binary Exponential Backoff) parameters. Analytical results are obtained by using an IEEE 802.11e user centric queuing model based on a bulk service M=G[1;B]=1=K queue, which is able to capture the main dynamics of the EDCA-based traffic differentiation parameters (AIFS, BEB and TXOP). The results show that the improvement achieved by our scheme on the overall VoIP performance is significant

THE ANALYSIS OF VARIOUS TCP SUB-VERSIONS AND MECHANISM FOR CONGESTION AVOIDENCE

TCP, the most widely used protocol on Internet, has a major problem in that its congestion control does not allow flows to obtain full bandwidth on fast-long distance links. A Performance analysis of TCP-controlled long file transfers in a WLAN in infrastructure mode also with Comparison and Analysis of Congestion Window for HS-TCP, Full-TCP and TCP-Linux in Long Term Evolution System Model 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 semiMarkov process considered in [1] and [2], but with arbitrary window sizes. We present simulation results to show the accuracy of the analytical model. KEYWORDS:-WLAN, ACCESS POINTS

A novel multipath-transmission supported software defined wireless network architecture

The inflexible management and operation of today\u27s wireless access networks cannot meet the increasingly growing specific requirements, such as high mobility and throughput, service differentiation, and high-level programmability. In this paper, we put forward a novel multipath-transmission supported software-defined wireless network architecture (MP-SDWN), with the aim of achieving seamless handover, throughput enhancement, and flow-level wireless transmission control as well as programmable interfaces. In particular, this research addresses the following issues: 1) for high mobility and throughput, multi-connection virtual access point is proposed to enable multiple transmission paths simultaneously over a set of access points for users and 2) wireless flow transmission rules and programmable interfaces are implemented into mac80211 subsystem to enable service differentiation and flow-level wireless transmission control. Moreover, the efficiency and flexibility of MP-SDWN are demonstrated in the performance evaluations conducted on a 802.11 based-testbed, and the experimental results show that compared to regular WiFi, our proposed MP-SDWN architecture achieves seamless handover and multifold throughput improvement, and supports flow-level wireless transmission control for different applications