A CSMA Media Access Control (MAC) scheme for supporting both centralized and
distributed
shared medium access control in a CSMA network. A master device exchanges connection
control messages with a slave during using contention-oriented access to establish
a connection and a session of periodic contention-free intervals. Once the session
is established, the contention-free intervals alternate with contention-oriented
intervals according to the timing parameters specified by the connection control
messages. Each of the contention-free intervals is divided into slots, the master
transmitting in a downstream frame and the slave device transmitting an upstream
frame in a following slot if the downstream frame indicates a source address matching
that of the master device, a contention-free access at a highest priority and a
connection number corresponding to the connection established between the master
device and the slave device, thus downstream frame thus serving to poll the slave
device and trigger the slave device's upstream frame. Master control is passed
from one device to another device during the contention-free interval using additional
control information, more specifically, a master flag for indicating which device
has master control and a control flag for indicating the direction in which master
control is being passed. Arrangements to change session parameters or change session
control are made using connection control messages using contention-oriented access.
Session control is passed from one device to another during a contention-free interval
following the exchange of appropriate connection control messages between the devices.
