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INFORMATION ABOUT DSL INTERNET CONNECTIONS
by Kirk van Druten, LANsharks Consulting

What is DSL?
Kirk's TCP/IP Networking White Paper (includes info on NAT, DHCP, Port Mapping, et.c)
What do I need to connect my computer/network to a DSL line?
ADSL vs SDSL
Choosing a speed for your DSL connection
Performance Reality Check
Why NOT PacBell DSL?

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What is DSL?
Digital Subscriber Lines are an inexpensive, relatively fast way to connect computers and/or networks to the internet. DSL lines run over the same type of copper wire your telephone uses and are always connected. Because of this always-on connection, there is no dialing, delays while connecting or annoying modem screeches. Simply open your internet browser or email progam and you're accessing the internet. It really is that simple.

What do I need to connect my computer/network to a DSL line?
DSL connections typically use a DSL modem box or DSL Router. In most cases the DSL router or modem is provided by the company that is providing the DSL connection.

These devices have a connection on the back for the DSL line as well as an ethernet connection. The ethernet connection can either plug into a) your computer or b) your network's ethernet hub.

ADSL vs SDSL
Digital Subscriber Line (DSL) technology comes (mainly) in two flavors: Asymmetrical DSL and Symmetrical DSL.

The speed of an ADSL connection inbound to your computer/network is faster than it is leaving. The assumption with ADSL is that the primary use of the connection is for web surfing and downloading email from a server outside your home/business. Getting things like web pages and email into your network/computer is much faster than sending things out (such as email file enclosures).

SDSL provides a connection with the same speed to and from your computer/network, and is usually faster than ADSL. This type of connection is much preferred in situations where you want remote users to have access to a shared database, file or email server on your network. Since this type of traffic leaving the network will use the maximum speed available, SDSL connections are much more performance oriented. SDSL is also much better for remote screen sharing applications, such as Timbuktu.

Both ADSL and SDSL (xDSL) technology are distance dependent and is affected by the amount of wire between your home/office and the telephone company's central office. The further you are away, the less speed options you will have. Your location must be within 2 miles of the central office.

*IDSL is available for locations that exceed 2 miles from the phone company's central office.

Great Expectations: Choosing a speed for your DSL connection
The speed of your connection depends on four things:
1. your intended use of the line (for example simple web surfing vs. sharing a database)
2. the number of simultaneous users using the internet
3. the distance you are from the phone company's central office and
4. your budget.

If you plan to use the connection for web access and email, the 192k or 384k connection speeds should suit your needs very nicely.

If you plan to have multiple remote users to accessing your file/email/web server or sharing a networked (i.e. FileMaker Pro) database, you'll want the fastest SDSL connection you can get/afford. The fastest SDSL connection runs at 1.1 megabits per second.

Performance Reality Check
Your local ethernet is fast by telecommunications standards. When thinking about the performance of remote users connecting to a shared database, note that your local 10-Base-T ethernet network has a capacity of 10 megabits per second. 100-Base-T ethernet runs at 100 megabits per second. Compared to even the fastest xDSL connection at 1.1 megabits per second, ethernet is fast. Therefore, even the fastest xDSL connection is a fraction of the speed/capacity of your local network. Opening a large FileMaker Pro database, even over a fast SDSL connection can take a while, when compared with the performance of ethernet on your local network.

Also note that the performance of any connection is limited by the slowest connection in the link. For example if the network on which the shared database lives is connected by a 1.1 megabit/second SDSL connection, but the remote user's connection is a 28,8 kbits/second modem, the performance for that user will be fairly pokey.

Why not PacBell DSL for your Network? (see a real customer's log of a botched PacBell install)
Given the opportunity to botch something, the phone company will do so. In the past 10 years of working with modems, ISDN and Frame Relay connections I've seen some incredible things. Many of the most humerous (but unfortunatley the most costly) stories are due to the phone company just plain blowing it really badly.

In California, Pacific Bell advertises DSL for under $50.00/mo. This is ADSL technology and includes ONLY ONE TCP/IP address. This means that the connection is designed for ONLY ONE COMPUTER. You can use Network Address Translation to connect more than one computer to a PacBell ADSL line but you'll need extra hardware/software to do so. See "About Network Address Translation" in my TCP/IP Networking white paper.

Among the other problems with using the phone company as your internet service provider (ISP), expect to wait for long periods on hold if/when your DSL circuit goes down. Also expect to go through a few different people before you get someone who can understand your problem and even more time on hold until you get someone who can fix it.

Expect other problems if you own your own domain and plan to have the phone company host it for you. If you host your own web, file and/or email server, I strongly recommend using a more experienced ISP.