Due to its timed-token MAC protocol, FDDI is suitable for transmitting real-time and non-real-time data. Several protocol parameters should be properly selected to satisfy the time constraints of the synchronous messages and to provide the maximum usage of the asynchronous transmission bandwidth.

In this study the effect of asynchronous threshold values on the behaviour of the ring is considered, and two methods are developed to calculate suitable threshold values for different purposes. In the first method the proper asynchronous threshold values are calculated to share out the asynchronous bandwidth between nodes in given proportions. In the second method, asynchronous data transmissions of nodes are limited by using appropriate asynchronous threshold values. By this way the actual TTRT can be reduced to facilitate meeting the real-time requirements od synchronous messages.