Decision Criteria for Managers

All other technologies that provide multimedia services either bypass, replace or require additions to, the existing copper infrastructure. DSL allows service providers to maximize their existing copper infrastructure. This is a significant benefit due to the fact that copper is the world's predominant access technology. There are approximately 650 million access lines worldwide and over 600 million of them are copper. With DSL technology expanding the capacity of copper lines, new interactive multimedia services can be as ubiquitous as telephone service.

Today, there are quite a few technologies being explored to deliver interactive multimedia services. However, technology should not, and cannot, be the only criteria used to make a product decision. When considering all of the options many other criteria are used to make decisions, including:

• Cost

• Return on investment

• Flexibility

• Manageability

• Time to market

Fiber optic technology is most often associated with deployment of interactive multimedia services. Although fiber is considered a more sophisticated technology and may be the optimal long-term choice, there are currently some drawbacks that are delaying full deployment. Cost and lengthy deployment time have delayed even the most aggressive service providers. Current estimates for total fiber implementation exceed 30 years and will cost hundreds of billions of dollars to install.

The proliferation of copper lines around the world has given the DSL modem a clear advantage over the leading alternative, cable modem. While copper phone lines are ubiquitous, cable is not. Cable is also not available at most business locations around the world.

The use of a standard phone line affords DSL a number of advantages such as:

• Speed - DSL service enables full use of the phone line's bandwidth, whereas, cable modem users will enjoy only a fraction of the cable modem's potential speed. As more cable modem users go online, everyone's throughput will be lower.

• Availability - As stated before, copper phone lines are installed in almost every home and business worldwide. Coaxial cable is not.

• Interactivity - DSL offers interactive capability in all its applications. Cable modems do not. For the most part, cable modems can only be used for "broadcast" to the customer.

• Security - Since cable modems operate on a shared line, security becomes an issue not present with DSL.

The end result is that users can count on the reliability and flexibility of DSL rather than worrying about a cable network fraught with problems and periods of downtime.

Why Consider Using DSL?

• DSL gives you an immediate competitive advantage. You can deploy DSL today and generate new revenues faster, thereby competing with other offerings such as cable, direct satellite TV or other carriers.



• It serves as a complementary technology to other services such as fiber.



• DSL uses the already existing copper infrastructure thus maximizing previous investments.



• Unlike cable or fiber solutions, most DSL deliver simultaneous voice and interactive multimedia services over the same phone line.



• DSL, since it is a dedicated "per subscriber" service, provides built-in security. This is important as on-line banking and home shopping transactions become popular.



• DSL offers service providers product investment protection. In geographic areas where high-volume subscriptions to DSL provide a cost justification to fiber provisioning, telcos can deploy fiber and reuse their DSL modems in new service locations.

Potential users of ADSL will need the following:

• An ADSL modem (compatible with the one at the NSP’s point of presence)
• A POTS splitter to separate voice and data transmissions (unless using ADSL Lite)

Providers of ADSL services will need modems and POTS splitters in their digital subscriber line access multiplexer (DSLAM) to terminate and aggregate incoming ADSL lines and redirect voice traffic to the public switched telephone network (PSTN) and data to a high-speed digital line (DS3, OC-3, or OC-12). The DSLAM is the major intelligence component in the ADSL system. It consists of central site modems and a service access multiplexer (SAM) that interfaces to the NSP’s ATM or Frame Relay backbone. The ADSL service provisioning model includes two types of DSLAM: the central office DSLAM is built for high density and concentration, while the remote DSLAM sits in the remote DLC system. Service providers will also need billing systems, testing and diagnostic functionality, and network management capabilities.

Significant development work is still needed by NSPs and equipment manufacturers alike to develop more affordable, scalable, interoperable, and easily provisioned ADSL systems. But this is an exciting emerging technology that will initially provide high-bandwidth local access for enterprise networks and teleworkers.