We study the capacity of multiple-access networks both on uplink and downlink. In our model each user requires a given signal-to-interference-plus-noise ratio (SINR) and the capacity region is obtained as a solution of a power allocation problem. In this paper, we emphasize the differences between uplink and downlink. The mathematical analysis of the capacity region is given in the framework of ergodic point processes and we show the links between the geometry of the network and its capacity region. On the downlink, we pay attention to various network architectures and levels of cooperation between base stations: macrodiversity, load balancing, and traditional cellular networks