On-line routing of real-time messages

Whether it is possible to have an optimal online algorithm for unidirectional ring, out-tree, in-tree, bidirectional tree, and bidirectional ring networks is discussed. The problem is considered under various restrictions of four parameters-origin node, destination node, release time and deadline. For unidirectional ring, it is shown that no such algorithm can exist unless one of the four parameters is fixed. For out-tree, it is shown that no such algorithm can exist unless one of three parameters-origin node, destination node and release time-is fixed. For in-tree, it is shown that no such algorithm can exist unless one of three parameters-origin node, destination node and deadline-is fixed. For bidirectional tree, it is shown that no such algorithm can exist unless the origin node or the destination node is fixed. For bidirectional ring, it is shown that no such algorithm can exist unless the origin node and either the destination node or the release time are fixed