通信网络时延受限且满足带宽要求的最小代价组播树问题是NP完全问题，传统方法难以求解，一般采用启发式方法求解。

The problem of minimum cost multicast tree satisfying bandwidth request and delay-constraint in communication network is a NP-complete problem. It is difficult to be solved by traditional methods.

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在组播树建立之初，计算好组播节点之间的最小代价路径，以便于出现故障之后寻找最优备用链路；

Using STP algorithm, the least cost paths between nodes are computed when computing the working tree, so the best backup path can be found as soon as the failure occurs.

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