What are the meanings of telephone (landline) single line, double line, analog and IP, and what are the differences? Please give a brief introduction. Thank you very much.

The first generation of traditional telephone, also called analog telephone, has only one line, so does the second generation of digital telephone. At present, IP telephone is based on IP network to transmit voice data, video and so on. IP phones can have several lines, usually two, and our company has six. The difference between them is that they use different servers. Traditional PBX uses circuit switching principle to realize the function of group telephone, while IP PBX uses TCP/IP protocol and packet switching principle to realize the same function on Ethernet. Moreover, on the basis of retaining all traditional PBXs, IP PBX adds the function of network communication. The shortcomings of traditional PBX can be listed as follows: dedicated, expensive, inconvenient to manage and maintain, and unable to simply realize CTI or VOIP. The emergence of IP PBX can solve these problems.