This paper considers access control for local area computer communication networks. We propose two distributed access control schemes for a bus network. The schemes are simple and asynchronous, and provide for collision-free communication among ports. In addition, one of the schemes provides a bounded, guaranteed time to transmisidon for each port. We also show that this scheme is efficient in the use of the bus bandwidth, in the sense that there is only a small fraction of time during which the bus is idle when there is at least one packet available for transmission.