因特网的迅速发展使人们对带宽的需求急剧增加 ,由此导致了波分复用系统在骨干网上的大量使用。同时随着ｘＤＳＬ、千兆以太网和无源光网络（ＰＯＮ）等高速接入技术的出现和推广 ,局域网的容量也得到了极大的提升。原本被认为具有足够带宽资源的城域ＳＤＨ环路 ,正逐步成为全 The rapid development of the Internet has led to a sharp increase in the demand for bandwidth. As a result, the WDM system has been widely used on the backbone network. Meanwhile, with the advent and promotion of high-speed access technologies such as xDSL, Gigabit Ethernet and Passive Optical Network (PON), the capacity of the local area network has also been greatly improved. The metro SDH loop, which was originally considered to have sufficient bandwidth resources, is gradually becoming full