Types of MLTS

The Federal Communications Commission (FCC) uses the term MLTS to describe Centrex, analog Private Branch Exchanges (PBXs), Integrated Services Digital Network (ISDN) PBXs, non-ISDN digital PBXs, Internet Protocol (IP)-PBXs, key systems and systems that use combinations of these technologies.¹

There are two basic technologies employed: 1) Legacy² and 2) packet-switched or IP-based, as shown in Table 1. The MLTS service is offered either 1) through equipment owned or leased and located at the customer premises, or 2) as a service hosted by the equipment manufacturer or on the carrier's network. Although the Commission has found that some MLTS types are close substitutes³, there are crucial differences between the basic types as to whether the business owner, carrier or equipment manufacturer operates the system, and in the regulatory regime under which they are offered.

Table 1: Types of MLTS

Technology/Site	Premise-based	Hosted or Network-based
Circuit-Switched, or Traditional, or Legacy	Analog PBX Digital or ISDN PBX Key System Hybrid Key System	Centrex (PacBell) CentraNet (Verizon California) Other LECs
Packet-Switched, or Next Generation, or IP-based	IP-PBX IPBX Voice over Internet Protocol (VoIP)-PBX	IP-Centrex IP-CentraNet Hosted/Virtual IP
Location of equipment	Customer premises	Local Exchange Carrier (LEC) Central Office or local switch, or Equipment Manufacturer's site

1 FCC DA 04-3874, Public Notice seeking comment, FN 2, December 10, 2004.

2 The term "legacy telephony environments" is used here to mean telecommunications generally in use before the recent wide adoption of packet-switched telecommunications. Examples of legacy telephony include the use of protocols such as analog, digital such as ISDN and other Time Division Multiplexing (TDM) based concepts. NENA 06-502 at 11.

³ Alternative Regulatory Frameworks for Local Exchange Carriers, D.94-09-065, September 15, 1994, at 190.