Two approaches are available to local-exchange carriers wishing to establish VoDSL service. One approach, broadband loop emulation service (BLES), extends Class-5 servicing office capabilities (custom calling and Centrex services, as well as trunking for customer premises equipment [CPE]), along with high-speed data services to customers over DSL (see Figure 5). Using the BLES approach, VoDSL vendors have designed equipment that interfaces with existing customer equipment, the DSL network, and the Class-5 switch (also called a local exchange in some countries).

Figure 5. BLES Architecture

Typically, a single piece of hardware is installed at the subscriber location and connected to the existing telephone system. This hardware is generally installed in the telephone wiring room of the building. Depending upon the vendor, the CPE and the DSL modem are separate pieces of equipment or can be integrated in a single unit. In most VoDSL implementations, the subscriber-side CPE is referred to as an integrated access device (IAD). Generally, the IAD provides an Ethernet or asynchronous transfer mode (ATM) port for data, and a number of voice ports for analog telephone lines, each representing a unique VoDSL circuit.

In the network, a voice or local-exchange gateway at the service provider’s CO sends the VoDSL voice traffic to the existing Class-5 voice switch via a standard network interface such as GR–303 or TR–08 in the United States or V5.2 for countries that use European standards-based equipment. This approach is generally most cost-effective where the service provider already offers traditional voice services over an existing switching network and wishes to offer additional revenue-producing voice services over existing infrastructure.