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New Technique to Enhance Quality of Service Support for Real Time Applications in EDCA Protocol

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Distributed Coordination Function (DCF) and Enhance Distributed Channel Access (EDCA) are two protocols which are used in Medium Access Control (MAC) layer. DCF sends its data without any differentiation between various data types. Real time application data such as voice or video do not have any preference to service it first. However the data with EDCA protocol are divided into four categories with different priorities. The voice category takes the highest priority, and then followed by video, best effort and background respectively. Specific EDCA parameters are used in each category. When using EDCA protocol, there is probability that the backoff time of two or more categories reach zero at the same time causing internal collision. Increasing the number of collisions will affect the Quality of Service (QOS) parameters requirement and decrease the throughput of the network. In this paper, the OPNET simulation is used to present some limitations in EDCA protocol with increasing the number of Voice Over Internet Protocol (VOIP) users and using default values of EDCA parameters. In addition to that, this paper proposed new technique to enhance EDCA protocol by adjusting contention window (CW) depending on the work load. Our technique will make EDCA protocol tolerates more VOIP users with achieving the QOS requirements. It will also decrease the collisions inside the network and increase the throughput.
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