  This paper presents an analytical model for the average frame transmission
delay and the jitter for the different Access Categories (ACs) of the IEEE
802.11e Enhanced Distributed Channel Access (EDCA) mechanism. Following are the
salient features of our model. As defined by the standard we consider (1) the
virtual collisions among different ACs inside each EDCA station in addition to
external collisions. (2) the effect of priority parameters, such as minimum and
maximum values of Contention Window (CW) sizes, Arbitration Inter Frame Space
(AIFS). (3) the role of Transmission Opportunity (TXOP) of different ACs. (4)
the finite number of retrials a packet experiences before being dropped. Our
model and analytical results provide an in-depth understanding of the EDCA
mechanism and the effect of Quality of Service (QoS) parameters in the
performance of IEEE 802.11e protocol.
