Upgrading and Repairing Networks

Chapter 16. Digital Subscriber Lines (DSL) Technology

SOME OF THE MAIN TOPICS IN THIS CHAPTER ARE

DSL and Cable Modems 258

The Future of DSL 267

DSL and cable modems are the fastest technology available today for accessing the Internet for home or small-office users. Although both of these technologies offer a very fast download speed, and a variable upload speed (depending on the service agreement), they are not a substitute for the T-carrier dedication connections, ATM, or even Frame Relay. Those technologies are for high-speed networks that require service-level agreements for bandwidth commitments or dedicated connections, whereas DSL and cable modems are for home workers, small offices, and home users who just want to have fun. Just because DSL and cable modems aren't a substitute for a T-carrier line doesn't mean that they are not a good solution for a small business, or a small business unit that is separated geographically from the main office.

For example, DSL and cable modems are perfect for branch offices, where the cost of a dedicated service (or the slowness of a dial-up service) aren't appropriate. DSL can enable a small office to upload and download significant amounts of information from a central network, or to other branch offices. Employing Virtual Private Networks (VPNs) can provide for security on an Internet connection.

Although DSL technologies (usually called xDSL because you can get different bandwidths and so on depending on the prices charged) are a good solution for a small business, there can be problems. First, DSL is not available in as many locations geographically as cable technology. Cable modems are easier to installmost of the time you only need to put a T-connector on your cable connection and run one cable to your television set (or set-top box) and use the other side of the T-connector to run a cable to your cable modem. For DSL, where it is available, you can experience disruptions when other lines are added or removed from the local loop. Some DSL flavors require you to use special devices to connect other phones at your location to the phone lines, or otherwise the voice channel can become degraded. In general, cable modems are simple to install, whereas DSL technologies can be more complicated. If you don't understand the technology, it can be difficult to do a self-install.

	See Chapter 46, "Virtual Private Networks (VPNs) and Tunneling," for detailed information on VPNs.

DSL comes in many flavors (described later in this chapter). If your telephone company can reach you within the limits imposed by DSL technology, you can be sure there will be more than one offer you can choose from. Some companies offer DSL service in a faster direction (upload/download) than other service categories. Others offer a standard home user package that gives a faster download time, with a slower upload time. The difference should reflect your own needs.

There are other things to think about when using DSL. For example, do you have a small network, and do you want to enable each node to access the Internet through this single connection? Do you have any policies set up for creating a firewall between your company network and the Internet? We'll explore these topics, along with others, in this chapter.