Congestion Avoidance mechanism in WLANs

Wireless LANs are continuously expanding not only in terms of coverage but also in terms of traffic and services. This tremendous growth is ought to the flexibility that IEEE 802.11 networks offer and also to the extremely low cost of those network´s components. Primary, the WLANs were used for office or home applications, in order to provide a wireless extension of the already existent wired LANs, the well-known Ethernet IEEE 802.3. The main services that were carrying, were legacy IP services, like HTTP browsing, FTP and email. These services have specific quality of service (QoS) requirements. WLANs have well-tested MACs mechanisms in order to satisfy these requirements. The carrier sense multiple access/collision avoidance, the RTS/CTS and the Fragmentation mechanisms, were satisfactory features for the above services and requirements. Nowadays, we have WiFi devices with much wide capabilities, like as VoIP phones, wireless cameras for home surveillance and multimedia adapters/bridges that bring such broadband services to the end-user. Those new applications, introduce new traffic, schemes profiles and of course much more restricted QoS requirements. On the other hand, there are new challenges for the multimedia services, which are being served over real-time transport protocol (RTP). The new key performance indicators that arising, are the jitter and the delay of packet delivery. Without sophisticated QoS mechanisms, the existing version of the 802.11 standard doesn´t optimize the transmission of voice and video. Thus, new requirements to provide guaranteed QoS in modern WLAN, bring to the foreground the need, for new WLAN MACs protocols, which are going to face up these challenges.