虽然现代城域网的设计在很大程度上借鉴了长途传输网的基本思想和实践经验，但是两个应用领域之间仍然存在着显著的差别。其中最重要的是，城域网要在保持成本尽可能低的情况下，支持更多的业务类型和数据传输速率。然而，对大多数光纤制造商来说，他们进入城域网市场较晚，且 Although the design of modern metropolitan area network largely draws on the basic idea and practical experience of long distance transport network, there are still significant differences between the two application areas. The most important of these is that metro networks should support more types of services and data rates while keeping costs as low as possible. However, for most fiber optic manufacturers, they enter the metro market later, and