555 research outputs found

    Performance Improvement Of Mac Layer In Terms Of Reverse Direction Transmission Based On IEEE 802.11n

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    Medium access control (MAC) layer is one of the most prominent topics in the area of wireless networks. MAC protocols play a big role in improving the performance of wireless networks, and there are many challenges that have been addressed by the researchers to improve the performance of MAC layer in the family of IEEE 802.11. The physical data rate in IEEE 802.11n may reach 600 Mbps, this high data rate does not necessary transform into good performance efficiency, since the overhead at the MAC layer signifies that by augmenting PHY rates the effectiveness is automatically reduced. Therefore, the main objective of next generation wireless local area networks (WLANs) IEEE 802.11n is to achieve high throughput and able to support some applications such as TCP 100 Mbps and HDTV 20 Mbps and less delay. To mitigate the overhead and increase the MAC efficiency for IEEE 802.11n, one of the key enhancements at MAC layer in IEEE 802.11n is a reverse direction transmission. Reverse direction transmission mainly aims to accurately exchange the data between two devices, and does not support error recovery and correction; it drops the entire erroneous frame even though only a single bit error exists in the frame and then causes a retransmission overhead. Thus, two new schemes called (RD-SFF) Reverse Direction Single Frame Fragmentation and (RD-MFF) Reverse Direction Multi Frame Fragmentation are proposed in this study. The RD-SFF role is to aggregate the packets only into large frame, while RD-MFF aggregate both packets and frames into larger frame, then divided each data frame in both directions into subframes, Then it sends each subframe over reverse direction transmission. During the transmission, only the corrupted subframes need to be retransmited if an error occured, instead of the whole frame. Fragmentation method is also examined whereby the packets which are longer when compared to a threshold are split into fragments prior to being combined. The system is examined by simulation using NS-2. The simulation results show that the RD-SFF scheme significantly improves the performance over reverse direction transmission with single data frame up to 100%. In addition, the RD-MFF scheme improvers the performance over reverse direction transmission with multi data frames up to 44% based on network condition. These results show the benefits of fragmentation method in retransmission overhead and erroneous transmission. The results obtained by ON/OFF scheme takes into account the channel condition to show the benefits of our adaptive scheme in both ideal as well as erroneous networks. In conclusion, this research has achieved its stated objective of mitigation the overhead and increase the MAC efficiency for IEEE 802.11n. Additionally, the proposed schemes show a significant improvement over the reverse direction in changing network conditions to the current network state

    A Dynamic Multimedia User-Weight Classification Scheme for IEEE_802.11 WLANs

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    In this paper we expose a dynamic traffic-classification scheme to support multimedia applications such as voice and broadband video transmissions over IEEE 802.11 Wireless Local Area Networks (WLANs). Obviously, over a Wi-Fi link and to better serve these applications - which normally have strict bounded transmission delay or minimum link rate requirement - a service differentiation technique can be applied to the media traffic transmitted by the same mobile node using the well-known 802.11e Enhanced Distributed Channel Access (EDCA) protocol. However, the given EDCA mode does not offer user differentiation, which can be viewed as a deficiency in multi-access wireless networks. Accordingly, we propose a new inter-node priority access scheme for IEEE 802.11e networks which is compatible with the EDCA scheme. The proposed scheme joins a dynamic user-weight to each mobile station depending on its outgoing data, and therefore deploys inter-node priority for the channel access to complement the existing EDCA inter-frame priority. This provides efficient quality of service control across multiple users within the same coverage area of an access point. We provide performance evaluations to compare the proposed access model with the basic EDCA 802.11 MAC protocol mode to elucidate the quality improvement achieved for multimedia communication over 802.11 WLANs.Comment: 15 pages, 8 figures, 3 tables, International Journal of Computer Networks & Communications (IJCNC

    Reverse direction transmission using single data frame and multi data frames to improve the performance of mac layer based on IEEE 802.11N

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    Reverse direction transmission and block ACK are effective ways to improve the performance of MAC layer that reduces the overhead and increases the system throughput. As high as 600 Mbps of physical data rate is achieved in IEEE 802.11n where high data rate of the current MAC layer leads to a high performance overhead and low performance throughput. Further,designing the MAC layer is still ongoing to achieve high performance throughput. In this paper, we examine the performance enhancement of the proposed 802.11n MAC layer in terms of reverse direction transmission using a single data frame and multi data frames. We implemented these schemes in the NS2 simulator to show the results for TCP traffic and compared them with the literature

    VoIP Call Admission Control in WLANs in Presence of Elastic Traffic

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    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

    Max-min Fairness in 802.11 Mesh Networks

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    In this paper we build upon the recent observation that the 802.11 rate region is log-convex and, for the first time, characterise max-min fair rate allocations for a large class of 802.11 wireless mesh networks. By exploiting features of the 802.11e/n MAC, in particular TXOP packet bursting, we are able to use this characterisation to establish a straightforward, practically implementable approach for achieving max-min throughput fairness. We demonstrate that this approach can be readily extended to encompass time-based fairness in multi-rate 802.11 mesh networks
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