Real-time local area networks like Fieldbus have to handle two types ofdata transfer, synchronous and asynchronous. The synchronous data is generated periodically and has to be transmitted before fixed deadlines. Asynchronous messages are generated by unforeseen events and thus cannot be predicted. The data transfer is handled in two different phases or time---windows. In this paper, we apply different algorithms that are known from the real-time schedluing discipline for real-time communication networks. Simplifications are made with respect to frame lengths and the resulting error is shown to be negligible for the type of data transfer considered. The algorithms generate the correct polling sequence for the data transfer automatically respecting the periodic deadlines. We also introduce dynamic mechanisms to extend time-windows and utilize the network bandwidth more efficiently. These algorithms are computed during the real-time operation of the network.