通信介质（传输介质）即网络通信的线路，有双绞线、 非屏蔽双绞线、 同轴电缆和光纤四种缆线，还有短波、卫星通信等无线传输。
链路层(link layer)提供了通信介质的物理接口(例如以太网设备)。
The link layer provides the physical interface to the communication medium (such as an Ethernet device).
塑料光纤是一种新型的光通信介质，在短距离通信领域得到了广泛的应用。
Plastic optical fiber is a new optical-communication medium, which is widely used for short distance communication.
家庭网络的实现要求经济和实用性，选择合适的通信介质将起到决定性的作用。
It is decisive that choose the appropriate communication medium, because the realization of home network request economy and usability.
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