Decentralized Control Mechanism Suppressing Delay Fluctuation in Wireless LANs

Real-time applications such as phone, videoconference, multimedia streaming, are typical applications which require relatively small delay and small delay fluctuation. To meet the QoS requirements of these applications, network infrastructures should have the ability to accommodate real-time traffic. Recently, IEEE802.11 wireless LANs, fundamentally based on CSMA/CA, have been widely used as parts of network infrastructures, so QoS support in wireless LANs becomes important. Several existing PCF-based centralized control mechanisms can support constant small delay of real-time traffic in a wireless LAN. However, these mechanisms require a centralized controlled coordinator, and cannot be utilized in any case. So, a decentralized control mechanism supporting real-time traffic is an important alternative solution to support real-time traffic. EDCF is a typical example of decentralized control mechanisms which provides relatively small delay for real-time traffic, but cannot achieve small delay fluctuation because of the burst feature of its backoff mechanism. We propose a decentralized control mechanism suppressing delay fluctuation in CSMA/CA networks, called DDFC (Decentralized Delay Fluctuation Control), and examine the performance of DDFC by simulation. The results of simulation confirm that we can achieve not only small delay but also small delay fluctuation in EDCF-based wireless LANs by controlling real-time traffic according to DDFC.