Is a Steiner Tree the optimal multicast model?

Many multicast routing algorithms have been suggested in the past as multicast communication emerges as one of the important services in communications networks. Many algorithms aim at the Steiner tree model because the Steiner tree is thought to provide the optimal multicast route by minimizing the sum of the link costs. The concept of cost in network routing can apply to various measures of network resource utilization, such as delay, bandwidth, buffers, number of links, etc. However, the Steiner tree is not always an ideal model to optimize all these cost factors because some performance factors, such as delay and bandwidth utilization, cannot be optimized by minimizing the sum of the link costs. In fact, the Steiner tree is ineffective with these two important factors delay and bandwidth which may affect the quality of the communication and the Steiner tree based heuristic algorithms may not be able to provide efficient multicast route. Therefore, the practical meaning of the cost factors to be optimized by the Steiner tree needs to be evaluated and the validity of the Steiner tree as an ideal multicast routing model should be reviewed. Two delay optimal trees are proposed as practical alternative models.