The type of the applications for which Internet is being used has changed over the years. Multimedia applications, Real-time applications and Game playing require Quality of service. IEEE has proposed IEEE 802.11e, a quality of service extension to the wireless LAN standard IEEE 802.11. In this paper service differentiation ability of 802.11e is evaluated. Identical traffic is considered for all Access categories to quantitatively differentiate different Access categories. The results indicate, 802.11e achieves service differentiation with some limitations. NS-2.26 is used for simulation.

Widespread employment of broadband networks, have been widely excited researchers and producers to develop and optimize this type of networks. This process is not possible, without study and deep preciseness in designing and type of the implementation of system. Recently introducing Worldwide Interoperability for Microwave Access (WiMAX) in communication world is invigorating researchers to devote their attempts in way of optimizing this favorite broadband networks. So in this paper, the possibility of transmission and regeneration of information and video pictures with acceptable signal to noise ratio (SNR) and bit error rate (BER) is provided by simulating physical layer of WiMAX system according to the IEEE 802.16-2004 standard. This simulation is done with MATLAB software and designed for approaching to appropriate quality and throughput in WiMAX networks. Simulation results shows that how video file in 'avi' format have been regenerated with an admissible quality after transmission in virtual designed space based on standard tested with 2-PAM and 64-QAM modulation techniques, simulation also shows how we can use peak signalto-noise ratio (PSNR) of pictures in adaptive modulation and coding (AMC).

Since there is no dierence between uplink and downlink subframes in the IEEE 802.16 mesh mode, both downlink and uplink tra cs are transmitted within a single time frame. Hence, in most scheduling methods, only one scheduling algorithm is used for both uplink and downlink tra c. However, because of the dierent characteristics of uplink and downlink tra c, dierent scheduling methods should be used for each of the tra c types. In this paper, we focus on the mesh centralized scheduling of downlink ow in the data subframe. After comprehensive analysis of the characteristics of downlink tra c, we propose a new algorithm, called Tra c-Aware Scheduling (TAS). In this algorithm, the downlink tra c distribution is tuned for maximum concurrent transmission rate. This goal is achieved by choosing dierent link selection criteria, such as maximum demandant sender, farthest receiver and least interfered path, based on the downlink tra c analysis results. The simulation results show that our algorithm outperforms existing methods in terms of scheduling length, link concurrency, and throughput (about 13.7% in average) for the downlink tra c. Moreover, the proposed algorithm is scalable. In particular, on average, 3% improvement is achieved in terms of scheduling length at higher tra c loads and in the number of nodes.