Firstly, the categories and related models of Digital TV are explained, as follows:

- Classified by the resolution of the picture, there is Standard-resolution Digital TV (SDTV) or High-resolution Digital TV (HDTV).

- By the mode of channel transmission, this is categorized into satellite, cable network and ground digital TV.

- By the most of encryption and payment, this is categorized into free and pay digital TV.

- By the different services provided, this is divided into digital TV broadcasting and interactive digital TV (interactive TV, ITV for short).

By the differences in technological features, interactive TV can be classified into semi-interactive digital TV (semi-interactive TV) and duplex interactive digital TV (duplex interactive TV). The former means the interaction between the user and the Top Box, and is achieved by running the interactive TV applications downloaded into the Top Box; the latter is achieved via the information exchange between the user and the service center of the cable network provider through the duplex communication module in the Top Box.

Usually, the types of digital TV services can be found through a combination of the categories mentioned above. The digital TV trial-broadcast in Shanghai in 2002 was a hybrid digital TV service performed on the cable network, supporting standard resolution video, and with both free and pay digital TV broadcasting and semi-interactive TV.