拓扑学上的光网络由边（光传输）和节点（光交换）组成。从业务属性出发，基于连接和无连接方式，分析了光交换的时间结构，包括光分组和光突发的时间结构，以及不同动态性的光电路交换的时长及其度量标准，结合实验结果分析了最短光电路交换的时长极限。从多端口和大容量的要求出发，重点讨论了基于微电子机械系统(MEMS)开关、波长选择开关(WSS)和阵列波导光栅(AWG)的三种光交换结构。分析了光交换结构的扩展方法，并讨论了光交换的几个具有挑战性的问题，包括缓存和能耗问题。通过分析，希望从时间和空间两个维度更清晰地认识光交换的本质及其与电交换的异同。

In topology, an optical network is composed of multiple edges (optical transmission) and nodes (optical switch). The service features and the time structure of optical switch stream supporting the service are discussed based on the connection and connectionless patterns. Examples include the length of optical packet and burst, and the length of optical circuit with high dynamic degree, which is defined in the internet engineering task force (IETF) standard. The measured results imply the achievable shortest length of optical circuits. The space architecture of optical switch is discussed. Examples include three architectures in terms of large port number and capacity, i.e., the optical switching structures based on micro-electro-mechanical system (MEMS), wavelength-selective switch (WSS), and arrayed waveguide grating (AWG). The architectural scalability of three ones discussed above is addressed. Some other challenging issues are also discussed, including optical buffer and power consumption. Hopefully, the paper is helpful for understanding the essence of optical switching and the relationship with the counterpart electronic switching.