Voice over DSL

In general, a Voice over DSL (VoDSL) system functions as an overlay solution to a DSL broadband access network,enabling a CLEC to extend multiline local telephone service off of a centralized voice switch.

For example, Jetstream's VoDSL solution allows up to 16 telephone lines and high-speed continuous data service to be provided over a single DSL connection. A VoDSL solution typically consists of three components.

• First, a carrier-class voice gateway resides in the regional switching center (RSC) and serves as a bridge between the circuit-based voice switch and the packet-based DSL access network.
  

• Second, an Integrated Access Device (IAD)resides at each subscriber premises and connects to a DSL circuit. It also serves as a circuit/packet gateway and provides the subscriber with standard telephone service via up to 16 analog POTS ports and Internet service via an Ethernet connection.
  

• The third component is the management system.

With VoDSL solutions, DSL broadband access networks now have the coverage, capacity, and cost attributes to enable CLECs to deliver local telephone services as well as data services to the small and mid-size business markets. It has already been established that DSL access networks have the right bandwidth to serve the data needs of small and mid-size businesses. With VoDSL access solutions, this is true for serving the local telephone service needs of those subscribers as well.

Some VoDSL solutions are capable of delivering 16 telephone lines over a DSL circuit along with standard data traffic. Because 95 percent of small businesses use 12 or fewer telephone lines, a single DSL circuit provides sufficient bandwidth to serve the voice needs of the vast majority of the market.

In addition, if more than 16 lines are required, most VoDSL solutions enable a provider to scale service by provisioning additional DSL connections.In addition to providing the right capacity for providing local telephone service, DSL broadband access networks are very efficient in the way they deliver service.

TDM-based transport services,such as a Tl line, require the bandwidth of the line to be channelized and portions dedicated to certain services, such as a telephone line. Even if a call is not active on that line, the bandwidth allocated to that line cannot be used for other purposes.

DSL access networks are packet-based, enabling VoDSL solutions to use the bandwidth of a DSL connection dynamically. VoDSL solutions only consume bandwidth on a DSL connection when a call is active on a line. If a call is not active, then that bandwidth is available for other services, such as Internet access.

This dynamic bandwidth usage enables providers to maximize the potential of each DSL connection, delivering to subscribers the greatest number of telephone lines and highest possible data speeds.

Because telephony traffic is more sensitive to latency than data traffic, VoDSL solutions guarantee the quality of telephone service by giving telephony packets priority over data packets onto a DSL connection.

In other words, telephony traffic always receives the bandwidth it requires and data traffic uses the remaining bandwidth. Fortunately, telephony traffic tends to be very busy over the course of a typical business day, so the average amount of bandwidth consumed is minimal.

For example, over a single 768-Kbps symmetric DSL connection, a CLEG could provide eight telephone lines (serving a PBX/KTS with 32extensions) and still deliver data service with an average speed of 550 Kbps.