The cost of a dedicated fiber access to the broad-band integrated services digital network (B-ISDN) is too high for small business and residential customers necessitating some from of resource sharing. Combining the asynchronous transfer mode (ATM) over a passive optical network (APON) with a suitable medium access control (MAC) protocol can provide significant cost savings and a reasonable bandwidth. In this way the customer line section can support broad-band services at an early stage. The MAC protocol presented in this paper places emphasis on service transparency aspects with an aim to incur minimal changes to the Local Exchange for APON connections. Sharing is effected through a reservation based time division multiple access method. The proposed MAC protocol is characterized by dynamic bandwidth allocation and multiple cell transmissions from each network termination in the upstream direction. This reduces waste due to the unavoidable synchronization preambles and other overhead.