In this paper, a new delay-enabled EDCF for the transport of real-time traffic over an IEEE802.11e wireless LAN is proposed. The proposed technique will drop any packet belonging to a conversational class when a maximum queueing delay is reached. The packets belonging to an interactive or a background class are not dropped due to the queuing delay. The performance of this new technique is evaluated and compared to the the standard EDCF when serving various traffic classes. The effects of the backoff parameters and the traffic composition on the transmission probability, the dropping probability, the medium access delay, and the throughput is investigated. It is believed that such study is imperative for the design of a mapping function between an inherently QoS capable network such as UMTS, and an IEEE802.11 LAN.

The ubiquitous presence of wireless terminals with multimedia and mobile support has become a complex challenge for the provision of a desired level of QoS. Two tiers of priority have been considered in the literature: one related to the state of the call, i.e. is it a new call or an existing call being handed over to the considered cell; and the second on the type of traffic being carried, i.e. is it real-time or non real-time. It is believed, however, that a third tier based on the terminal mobility should be considered also. In this paper, the effects of the mobility on the network performance will be investigated, and a priority hierarchy between the three levels will be suggested.

The authors extend earlier work (ibid., vol.36, p.834-44, Jul. 1988) in modeling video sources using interframe coding schemes and in carrying out buffer queueing analysis for the multiplexing of several such sources. The previous models and analysis were suitable for relatively uniform activity scenes. Here, models are considered for scenes with multiple activity levels which lead to sudden changes in the coder output bit rates. Such models apply to talker-listener alternating scenes, as well as to situations where there is a mix of dissimilar services, e.g., television and videotelephony. Correlated Markov models for the corresponding sources are given. A flow-equivalent queueing analysis is used to obtain common buffer queue distributions and probabilities of packet loss. The results demonstrate the efficiency of packet video on a single link, due to the smoothing effect of multiplexing several variable-bit-rate video sources.>