a medium access control apparatus and method for use in a channel overlay network of a wireless access system . the wireless access system , which is based on a multi - carrier , includes a plurality of physical modules for receiving signals from a plurality of terminals , a plurality of mac modules for processing the signals received via the physical modules while being classified according to predetermined traffic classes , and a controller connected to the mac modules for integratedly managing the mac modules . the mac apparatus includes an additional mac module used for a control channel and a plurality of mac modules for supporting various qos traffic data according to individual classes , thereby improving scheduling complexity in a mac layer .