用户交换机 （ＰＢＸ）是一种专用 交换机，它完成企业内部之间以及与外部的电话交换，是市通信网的主要组成部分。随着通信技术的发展，特别是程控交换技术的不断发展，出现了一种新的用户交换机形式——集中式用户交换机（ＣＥＮＴＲＥＸ）。 集中式用户交换机是将原先建立 The PBX is a private branch exchange that performs telephone exchanges both inside and outside the enterprise and is a major part of the municipal communications network. With the development of communication technology, especially the development of program-controlled switching technology, a new form of user switch, Centrex, has emerged. Centralized user exchange is the original establishment