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This standard describes an interface between a telecommunication carrier network and a customer installation in terms of their interaction and electrical characteristics. In this standard, the telecommunication carrier network is referred to as the Network and the customer premises wiring and equipment as the Customer Installation (CI). The interface between the Network and the CI will be known as the Network Interface (NI). The NI is the same as the demarcation point defined in Part 68 of the FCC Rules and Regulations.

This standard covers the interface where the CI provides loop-start supervision. At this interface, the CI provides a supervisory loop-start dc voltage source and the network provides a voicegrade transmission path with dc loop signaling. This interface is designated an off-premises station interface in TIA/EIA-IS- 968-2001. It is typically used at the CI switching system (for example, PBX) end of off-premises station (OPS) lines; however, it is not limited to PBX applications.

This interface is illustrated in Figure 1. This interface is intended to work with an interface located at the far end of the network transmission path that uses loop-start signaling. In this standard, where it is necessary to discuss the far-end CI, T1.401- 2000, Network-to-Customer Installation Interfaces − Analog Voicegrade Switched Access Lines Using Loop-Start and Ground-Start Signaling¹, is referenced as appropriate. Several telecommunication carriers may be involved in providing the transmission path between the NI and the far-end CI. Intermediate carrier-to-carrier interfaces are not covered. This standard also does not cover the voicegrade transmission performance of the network or the CI. Dual-Tone Multifrequency (DTMF) signals are considered voicegrade signals; thus, DTMF signaling is not specifically discussed in this document.

Voltages and currents may appear at the NI as the result of:

- Normal operation;

- Network maintenance activities; or

- Abnormal conditions in the network environment² (e.g., induced voltages and currents, lightning hits) and in the CI environment.

Normal operation and network maintenance activity voltages and currents are covered by this standard; abnormal network or CI environmental voltages and currents are not.

¹ This document is available from the Alliance for Telecommunications Industry Solutions, 1200 G Street N.W., Suite 500, Washington, DC 20005.< http://www.atis.org >

² Telcordia Technical Reference TR-EOP-000001 describes abnormal network environmental voltages and currents that can occur at the NI.