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.