IEEE 802. 11e is standardized to enhance real-time multimedia applications’ Quality of Service. This standard introduces four access categories for different types of applications. Each access category has four adjustable parameters: Arbitrary Inter-Frame Space Number, minimum Size of Contention Window, maximum size of Contention Window, and a Transmission Opportunity limit. A Transmission Opportunity limit is the time interval, in which a wireless station can transmit a number of frames consecutively, without releasing the channel and any further contention with other wireless stations. Transmission Opportunity improves network throughput as well as service differentiation. Proper Transmission Opportunity adjustment can lead to better bandwidth utilization and Quality of Service provisioning. This paper studies the dynamic adjustment of Transmission Opportunity in IEEE 802. 11e using a game-theory based approach called Game Theory Based Dynamic Transmission Opportunity. Based on the proposed method, each wireless node chooses its appropriate Transmission Opportunity according to its queue length and media access delay. Simulation results indicate that the proposed approach improves channel utilization, while preserving efficiency in WLANs and minimizing selfishness behaviors of stations in a distributed environment.

Transmission Opportunity and contention window are two important parameters in media access in IEEE 802. 11e-based networks. and determine how to access the channel, as well as the length of time the channel is used. In these networks, each wireless station determines its media access probability by adjusting its contention window size. After winning in the contention, with respect to the duration of its Transmission Opportunity, transmits its data packets without re-contention. In multi hop networks, because of long distances between the source nodes and the destination nodes, the middle nodes are used to relay the data. Therefore, the middle nodes, in their Transmission and receiving range, see more nodes as neighboring nodes, which makes it possible to increase traffic intensity and higher collision rates than other nodes. In this paper, the length of the queue, data arrival rate and the amount media access delay are exploited in order to a dynamic setting of the Transmission Opportunity and contention window to reduce the rate of packet loss and end to end delay. Simulation results show the proposed method improves media access and reduce the amount of packet loss and delay.

Introduction: The risk of being affected by infectious diseases in dentistry directly depends upon the degree of contact with body liquids, such as blood and saliva, as well as the working tools. Different micro-organisms including the viruses causing AIDS and Hepatitis B as well as oral thrush are possible to be transferred in dentistry. According to the Dental intervention (FDI), it is suggested that all dental patients, in spite of the healthy look, are considered to be infective. Therefore, the health principles and protective and safety methods must be observed in all the sequences to prevent cross-infection. Thus, the present study seeks to investigate the degree to which the dentists in Isfahan respect and approach to such standards.Materials and Methods: This is a cross-sectional descriptive study. In order to answer the questions of the study (as found in tables 1&2), the data related to the participants’ attitudes and performance were collected by having them fill out a questionnaire and a checklist. A total of 140 dentists in Isfahan were selected through a random sampling in 1385 (HS). The data collected was then evaluated with SPSS.Results: The mean score obtained from the attitude-related questions was 5.36. Also, the mean score of performance-related questions was found to be 8.03. No significant relation was found between the dentists` attitudes and the years of service (P=0.092, r=0.17). No significant relation was found between the dentists` performance and the years of service (P=0.12, r=0.15). No significant relation was found between the dentists` attitudes and their performance (P=0.1, r=0.16).