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First, loop trunks, switch trunks, digital trunks
Loop trunk: refers to the general operator lines (such as: Telecom, China Unicom, China Netcom, Railcom, etc.), commonly known as "external lines" or landlines.
Telephone exchange trunk: refers to the number of common external lines bundled into a number, this number is called "quote number", as long as the external announcement of the lead number, you can reach several telephone numbers at the same time.
Digital trunk E1: Digital trunk is divided into NO.1 signaling, NO.7 signaling, PRI (30B+D), E1, and so on. Digital trunking is a data transmission network that uses digital channels to transmit data signals. Its main function is program-controlled switchboard and program-controlled switchboard to realize optical fiber 2M access, generally refers to 30B+D (that is, 30 voice signals + data signals), in other words a digital trunk E1 is equivalent to 30 external lines, but digital program control The extension of the switch is a direct dial outside line. All extensions can also implement an outside line number, and can also implement hundreds of outside line numbers. (For example: 1 digital trunk E1 + 100 digital program-controlled switches, users can apply for 200 number segments. You can also just one number)
Second, the advantages of switch trunks:
Trunks can only publish one number to the outside world, which is convenient for people to remember, facilitate the construction of hardware platforms, reduce traffic loss, and enhance corporate image. For example, the telephone exchange trunk: A B C D E F G H I J K is made into ten lines, and only externally announced: A number, namely: the lead number, the other 9 numbers are bundled under this number. At the same time dial: A can call nine phones at the same time.