A queueing model with batch arrivals for studying the impact of fragmentation in wireless protocols

Many wireless protocols (including 802.11 definitions) consider fragmentation a valuable approach to minimise the number of transmissions which are lost due to errors. Deciding the optimum size of the fragments is a problem that has been deeply studied in literature. In this paper we consider a different perspective: we propose a Markovian queueing model capable of predicting important performance measures - e.g., the expected response time, the expected number of enqueued packets - of protocols that adopt fragmentation as a mechanism for improving the maximum system throughput. Modelling the fragmentation is a non-trivial problem because batches of fragments have to be handled and the coefficient of variation of the time required to send a fragment is usually very low since almost all the frames tend to have the same size. We use the model to derive some performance indices under two scenarios: a multimedia transmission and a secure, encrypted, communication.