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The interest about distributed network architectures is arising. It allows to obtain more scalable network and in this context, also the interest of research around the IEEE 802.16 distributed mesh mode is growing. The mesh distributed mode supported by IEEE 802.16 protocol, with the capability to establish direct links between SSs (Subscriber Station) and with the wide coverage area and the promised bits rate, allows to create interesting scenarios. The protocol defines guidelines to realize request/grant process, but it presents some lacks, one of these is the absence of a distributed call admission control (CAC) algorithm. This process is essential to guarantee QoS constraints to admitted connections. In this paper, we present GCAD-CAC (Greedy Choice with Bandwidth Availability aware Defragmentation): a new call admission control algorithm to guarantee the respect of data flows delay constraints defined by three different traffic classes. To reach good results, the algorithm tries to accept all the new requests, but when a higher priority request is received, a lower priority admitted request is preempted. The preemption can leave in data subframe some little gaps not sufficient to new connection admission; these gaps can be collected by GCAD algorithm by activating a bandwidth availability based defragmentation process. The algorithm quality is proved by a comparison with other two algorithms found in the literature.