Limited bandwidth and high packet loss pose a serious challenge for video streaming over wireless networks. Even when packet loss in the medium is not present, the fluctuating available bandwidth due to varying number of active flows in a network causes problem for video streaming applications. In this paper, we propose to employ a novel admission control together with a ratedistortion optimized framework to maintain reasonable qualities for multiple concurrent video streams. In particular, we formulate an optimization problem to allocate the optimal transmission rates for each layered video streams jointly with the MAC protocol of a slightly modified 802.11x network. We show the hardness results of the optimization problem under various conditions. Furthermore, we show that a simple greedy layer-allocation algorithm is typically not optimal, although it can approximate the solution reasonably well under certain assumptions.