This standard contains voice transmission performance and compatibility requirements for digital wireline telephones including ISDN voice terminals intended for connection to a public ISDN and digital proprietary telephones connected to the ICs interface of an ISPBX as specified in the ISPBX Loss Plan section of ANSI/TIA/EIA-464-B. These requirements should ensure satisfactory voice service to the user in a high percentage of installations, both initially and over some period of time, as ISDN service becomes more ubiquitous and as changes occur in telephone serving equipment. However, because of the wide range of central off ice switching equipment, PBX equipment, customer apparatus, and loop plant used in North America, conformity with this standard does not guarantee acceptable performance under all possible operating conditions. In general, where two levels of acceptability are specified (desirable and mandatory), compliance with the criteria in the desirable category implies a higher probability of acceptable performance or compatibility. These requirements apply to terminals that encode and decode analog signals in conformance with p-law PCM and 64kbit/s as described in ITU Recommendation G.711. These requirements are not intended to describe specific requirements for the following types of digital voice terminal equipment: ISDN terminal adapters, ISDN cellular voice, terminals, ISDN terminal speakerphones, and proprietary digital telephones designed to be connected to systems whose loss plan is different from ANSITTINEIA-464-B. A digital telephone complies with this standard if it meets these requirements when manufactured and can be expected to continue to meet these requirements when properly used and maintained. This standard is limited to digital telephones employing a close-speaking microphone and an earphone that permit a single user to carry on a two way real-time voice communication, e.g., handset type telephones. This standard is also limited to telephones with linear, e.g., noncarbon, technology transmitters. The standard is intended to be in conformity with Part 68 of the Federal Communications Commission (FCC) Rules and Regulations, but is not limited to the scope of those rules. In the event that Part 68 requirements are more stringent than those contained in this standard, the provisions of Part 68 apply. The telephone will also be subject to the applicable environmental conditions specified in EIA/TIA-571. The standard does not contain safety requirements. Compliance with the applicable UL and CSA safety standards may be required in certain locations.