!!! Overview
[{$pagename}] ([ISDN]) is a set of communication standards for simultaneous digital transmission of [voice], [video], [data], and other network services over the traditional circuits of the [Public Switched Telephone Network]. 

[{$pagename}] was first defined in [1988|Year 1988] in the [CCITT] red book.[1] Prior to [ISDN], the telephone system was viewed as a way to transport [voice], with some special services available for [data]. The key feature of [ISDN] is that it integrates speech and [data] on the same lines, adding features that were not available in the classic telephone system. 

!! More Information
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