32传输介质 光缆 Item LED Semiconductor laser Data rate LoW High Fiber type Multimode Multimode or single mode Distance Short Long Lifetime Long life Short life Temperature sensitivityMinor Substantial Cost Low cost Expensⅳe 网络和现代通信技术基础—一物理层网络和现代通信技术基础——物理层 光缆 3.2 传输介质