Whilst there are several technologies that are superficially similar to the PSDN, such as Integrated Services Digital Network (ISDN) and the Digital Subscriber Line (DSL) technologies, they are not examples of it.
虽然有几种技术与PSDN表面上很相似，例如综合业务数字网（ISDN）和数字用户线路 （DSL）技术，但它们并非PSDN的一种。