This Standard addresses technical issues associated with MLTS support of Enhanced 911 Emergency Calling Service. It specifically addresses dialing, routing, local notification and network interface technical specifications associated with outgoing 911 calls from MLTS stations. It does not address technical issues associated with incoming 911 calls to MLTS equipment that may be used in a PSAP. This standard also does not address the unique considerations that apply to multiple extensions that pick-up on a single line. Nor does it address the unique considerations that apply to 911 calls made by persons with hearing or speech disabilities, who require the use of text telephones.

The formulating committee recognizes that many new techniques are being explored to provide MLTS support of Enhanced 911 calling. One of the more promising techniques involves the use of an ISDN interface. Enhanced 911 call ISDN signaling requirements in accordance with ANSI Standard T1.628a-2000 [Normative Reference 8] are included in this Standard. Any Enhanced 911 Calling Services using an ISDN Trunk Interface and operating methods other than as specified in this ANSI Standard are out of the scope of this Standard.

The committee also recognizes that MLTS support can be provided through a variety of adjunct equipment. This standard does not address these systems. In addition, it does not address Enhanced 911 support from mobile and wireless (PCS) telephones. It does, however, address wireless PBX stations Enhanced 911 support.

This standard does not address systems connected to public or private networks using Voice over Internet Protocol (VoIP). See IP Telephony Support for Emergency Calling Service TIA/EIA -TSB 146 [Informative Reference 5].

This Standard does address Enhanced 911 support regulations in effect at the time of publication. The Federal Communications Commission (FCC) in Docket No. 94-102 [Normative Reference 11] proposed regulations concerning MLTS equipment support of Enhanced 911. Docket No. 94-102 remains open and the FCC has imposed no regulations. Some States, however, have enacted legislation and imposed regulations concerning MLTS support of Enhanced 911 for varied MLTS Operators utilizing several methods. Subsequently, the National Emergency Numbering Association (NENA) convened an ad hoc group consisting of regulators, manufacturers, and other interested parties to develop model legislation that provides for uniform rules and regulations to be promoted at the State level for Enhanced 911 support. The terminology utilized in this Standard is aligned with the definitions used in the NENA Enhanced 911 Multi-line System Model Legislation developed by NENA. (See NENA Enhanced 911 Multiline System Model Legislation [Informative Reference 3]).