By Bob Niederman
December 6, 1999

Digital Subscriber Line (DSL) is a technology that promises to solve the "last mile" problem for many home and small business users - the slow speed at which a computer is connected to the Internet.

DSL features speeds many times faster than dial modems or Integrated Services Digital Network. My DSL line, for example, runs at 1 million bits per second (mbps). A typical dial modem may deliver 33 to 53 thousand bits per second (kbps). Therefore, this DSL line is at least 20 times faster than a dial modem.

Note that DSL comes in a bewildering number of varieties and speeds. Placing an additional letter in front of the ‘DSL’ differentiates some of the types of DSL, so generic references to DSL are sometimes written as 'xDSL'.

The speed achieved by your DSL connection can vary greatly depending on the type of equipment used, your distance from the telephone company central office (CO), and the quality of wire used from your home or apartment. According to one DSL vendor, distance correlates to speed as follows:

• Less than 9,000 feet (1.7 miles) = 1.024 Mbps (megabits per second)


• Less than 10,500 feet (2.0 miles) = 784 Kbps (kilobits per second)


• Less than 14,600 feet (2.8 miles) = 416 Kbps


• Less than 18,000 feet (3.4 miles) = 320 Kbps


• Over 18,000 feet = service may not be available

These distances reflect the length of wire, which may be significantly greater than the actual distance to the CO. Per the vendor, these estimates of the connection speed are conservative. You will not know the exact speed of your connection until your modem is installed.

It is interesting to note that this vendor estimated my distance from the CO at 14917 feet, which in the proceeding correlates to 416 kilobits per second. Yet at the time of installation, I ended up with a line at 1 megabits per second. It is also interesting to note that DSL service isn't available beyond a certain distance from the CO, so not everyone can get DSL.

This product may well become considerably cheaper in the near future in light of the recent Federal Communications Commission (FCC) decision requiring local telephone companies to share their phone lines with other providers of DSL.

Types of DSL service

Some types of DSL can use existing voice phone lines; others require installation of an additional line. Single-line DSL (SDSL) is configured such that the speed from your PC to the Internet ('upload' or 'upstream') and from the Internet to your PC ('download' or 'downstream') is the same. This is useful if you plan to have a web site at your end of the DSL, or if you wish to send large files to other places on the Internet.

Asymmetric DSL (ADSL) has a lower speed from your PC to the Internet than from the Internet to your PC. This is used to maximize the benefit of the more typical pattern of use, which usually involves sending small amounts of data to make requests for web pages, which in turn may require large amounts of data in the form of graphics or audio/video content to be sent to the user. ADSL can sometimes share the wires used for a voice telephone line, resulting in decreased cost. However, there are some reports of this possibly producing interference between the voice and data services.

Other Features

Private vs. Globally Unique Internet Provider (IP) Address

A private IP address means that most people on the Internet will not be able to initiate a connection with your machine. Others on the Internet can contact your PC if it has a Globally Unique IP address. A globally unique IP address would be required to start a World Wide Web site. Most home DSL contracts forbid commercial Web sites being run on a home service. (See below under 'Security Concerns' for more information on private IP addresses.)

Cost

Costs can be recurring (typically monthly) or there can be one-time initial costs for installation and/or for a DSL modem. The two services for which I compared prices were as follows:

Feature	Service "I"	Service "T"
Initial costs:
installation	$150	$99
DSL modem	$300	$0
inside wiring	$100/hour	$0*
* If you're in an apartment building and the inside wiring requires more than 100 feet of wire, some charge may be assessed.
Recurring costs:
monthly	$80	$49
Other:
Address	private	non-private
Length of Contract	1 year	1 year

Each of these services also provides e-mail and Usenet services. As illustrated, service "T" was less expensive. These prices were from August of 1999, before the FCC decision about line sharing. Prices may decrease significantly due to that decision. It pays to do some comparison-shopping.

Security Concerns

There are many people on the Internet who derive pleasure from breaking into other people's computers on the Internet. When you have a DSL connection, your machine may be more vulnerable than when you use dial-up Internet access.

If your IP address doesn't belong in the ranges noted above, your IP address is not private and therefore anyone anywhere on the Internet can attempt to initiate communications with your PC. If your ISP has implemented a firewall or other protective measure, as is the case at the Bank, not everyone on the Internet can attempt to initiate communications with your PC. While there are advantages to having an IP address that is globally unique, there is also a potential risk exposure to possible attackers.

URL references 2 through 5 are security related. I have not evaluated the software being sold through references 3 and 4 and this should not be considered a recommendation for that software, but instead as a starting point for evaluating such software. (Reference 5 appears to be very good as a first step.) Additionally, any software or configuration changes you make should be done on personal, rather than Bank PCs, since Bank PCs are reserved solely for Bank business, as noted in the pre-login message.