According to the delivery signaling, transmission mode and functions that can be achieved, enterprise fixed phones are mainly divided into:
A direct telephone is a type of telephone, meaning that the user uses it independently and owns a separate telephone number.
Analog trunk refers to the telephone line connecting PBX, telephone exchange (including telephone connector with switching function), wireless paging station, program-controlled telephone exchange, etc. and local exchange. Analog trunks are bundled together by multiple telephone channels and use the same number as a pilot number and access number to provide a unified number line for enterprises and institutions.
30B+D digital trunk refers to the 30B+D that users occupy an E1 (ie 2Mbit/s) port and access user switching equipment to provide users with a fully transparent transmission channel. The user switch is interconnected with the central office through the E1 line Each E1 has 30 user channels and one signaling channel. Protocol transmission is performed through signaling. One E1 can provide 30 channels of voice at the same time and provide N pilot marks (DID/DOD function).
Centrex is to use the resources of the public telephone network to form a private network to provide public network users with the special switching function of a virtual PBX (Private Branch Exchange, private branch exchange) service, so it is also called a centralized user branch exchange or virtual user exchange.
Digital trunk (NB+D) is a communication network developed based on the integrated digital telephone network (IDN). It can provide end-to-end digital connections. Unlike analog trunks, it provides analog voice signals and voices of digital trunks. The signal transmission is all-digital, the call quality is more excellent, and the DID/DOD function can also be activated.
Function introduction of DID and DOD The I in the DID means IN, and the O of the DOD is OUT. In simple terms, it means that the telephone realized on the digital trunk line directly calls in and out. Among the 8-digit telephone numbers, the first 4 digits are the trunk number of the branch office program-controlled switchboard, and the last 4 digits are the extension number of the branch office program-controlled switchboard. The last 4 digits are both the employee's extension number, and the first 4 digits are combined to form a personal straight line number for the employee, or it can be understood that after the digital trunk is used to activate the DID/DOD function, each employee has only one phone on the desktop. In the situation, there are both company extensions and dedicated personal direct telephones, which greatly improves office efficiency.