MEOW with CATS: multimedia extensions over wireless with CTS-assisted transmission scheme

With the advent of the IEEE 802.11e QoS standard, an interesting issue that arises is the provision of QoS support for legacy 802.11 terminals. In this paper, we present an access point-based overlay to the 802.11 DCF protocol that provides priority access to standard endpoints without requiring any client modifications. This technique can be used to provide preferential channel access to legacy endpoints in 802.11 networks, thus allowing the use of legacy 802.11 equipment even with such legal requirements. The use of clear-to-send (CTS) frames underlies this technique and hence we call it CATS, the CTS-assisted transmission scheme. Our technique works by positioning a quiet window straddling the expected time when a protected endpoint becomes ready to transmit. We present two variants of our method depending on whether or not the access point (AP) is able to directly observe the signaling. Using time-stamped traces of VoIP frames, we evaluate the performance of CATS. We also provide a simplified efficiency analysis of CATS.