This document compares, in an orderly manner, the transmission requirements in ANSI/TIA-464-C-2002, "Requirements for Private Branch eXchange (PBX) Switching Equipment" and those in ES 201 168 version 1.2.1, "Speech processing, Transmission and Quality aspects (STQ); Transmission characteristics of digital Private Branch eXchanges (PBXs) for interconnection to private networks, to the public switched network or to IP gateways".

Since only the PBX transmission requirements in ANSI/TIA-464-C and ES 201 168 are compared, it is necessary to examine relevant portions of the scope of each of these standards to gain an overall idea of the scope of the comparison. ES 201 168 provides transmission requirements while ANSI/TIA-464-C provides transmission requirements as well as other PBX parameters, e.g., signaling and supervision. All appearance of ANSI/TIA-464-C in this TSB includes ANSI/TIA-464-C-1 "Telecommunications – Multiline Terminal Systems – Requirements for PBX Switching Equipment, Addendum 1.