What is DSL?

     DSL (Digital Subscriber Line) is a technology that provides high-speed access to the Internet via existing copper wire telephone lines.  DSL provides a direct "always on" connection to the internet via your service provider.  A DSL modem is required and is normally supplied by the DSL provider you choose, since DSL standards vary widely and the modem must be compatible with the equipment your provider uses.

     If you want to have a number of systems share your DSL Internet access, via a network, it is necessary to have a hub, a router, or a router/hub combination.  Some DSL providers will offer a combined router/hub/modem all-in-one.  In almost all cases, the involvement of the DSL service provider ends when they have provided you with DSL access and the hardware.  Getting the DSL setup and running on a network is not part of their pricing/package and will be your responsibility.  This is where TCD can help. We have customers running networks and sharing their DSL connection.  We know what equipment is needed, what routers work with dynamic IP addresses and PPPoE protocol, and always try to provide the most economical solutions for our customers.  Call us BEFORE you commit to a DSL provider so we can advise you on what would be your best solution.

DSL Info

     There are many varieties of DSL, but the ones most individuals or small to medium businesses would use are:
     SDSL (Symmetric Digital Subscriber Line) - This provides the same bandwidth (speed) in both directions, upstream and downstream.   Whether you're uploading or downloading you get the same performance.
     ADSL (Asymmetric Digital Subscriber Line) - Provides an upstream speed that is a fraction of the downstream speed.  The ADSL line is divided into two channels, which allows you to have a normal phone/fax line on the smaller channel and DSL on the larger one.  This simplifies wiring but a splitter or filter is required to separate the voice part from the data part.  This is primarily used for residential applications.
     IDSL (ISDN Digital Subscriber Line) - This is similar to SDSL.  The bandwidth (speed) is symmetrical but it operates at lower speeds than SDSL and can be used for longer distances.  

PPPoE

    PPPoE stands for point to point over ethernet.  It is a method of encapsulating your data for transmission and was originally designed for dialup lines.
     With a PPPoE setup, your computer needs to run a PPPoE protocol stack (software).  The particular software will be recommended, or supplied, by your DSL provider.  One of the more common PPPoE stacks is WinPOET, which is used by Verizon (Bellatlantic).  There are some common problems with PPPoE and DHCP, NAT, and other issues.  If you have a choice it is recommended to get a bridged static IP, although it is generally more expensive.

Availability

     The twisted pair phone lines that carry DSL are not shielded from interference.  Therefore there are limits on the distance DSL signals can travel before degrading the maximum DSL speeds available in all DSL standards.  This distance limitation of DSL is only one of the technical hurdles that can hinder a DSL installation.  Other problems include old copper circuits, wire too thin, load coils, bridge taps, DLCs, bad connectors, etc.  These can all potentially ruin the chance that a local loop can provide DSL service, or rule out some of the faster speeds available.  In the U.S., approximately 50% of the people cannot currently get DSL, either because they are too far from the CO, or their CO is not DSL enabled yet, or they are behind some telephone architecture that is not DSL compatible yet.  I am providing a link to a sight that will allow you to check on your distance from a CO, the availability of DSL to you and the providers who can service your location.   There is also information on the speeds and cost for you. 
Click on DSL QUALIFICATION to check it out.  Good luck!

Sharing

     A single external DSL modem and a single computer.  The DSL modem bridges your PC to your internet provider.   Your PC has a public IP address and you must run some software firewall to increase security.
     You must use a CAT5 cable from the modem to your NIC card in the PC.  Cat5 cable has RJ-45 connectors on each end.

     A hardware firewall device is usually configured using your web browser, or via telnet.  This provides excellent security when properly configured.  If you want to allow outside connections into your system the firewall must be configured correctly to permit the access.  A firewall will usually allocate a private IP address to your PC.  A CAT5 straight-thru or crossover cable may will be required.

     ISPs may offer additional public IP addresses for, of course, an extra charge.  You can take advantage of this to share your DSL with multiple PC's by using an inexpensive hub or switch.

    Your PPPoE software talks to your ISP to allocate you an IP address for your login name and password.  Some ISPs do not yet limit the number of times this can be done, allowing you to login on more than one PC, thus getting internet access on all of them with no extra configuration or cost.   This may not work if your ISP does not support it (limits you to 1 IP address).

     This setup is very popular, works with many providers, is economical and secure.  These boxes are becoming very reasonably priced and solve a lot of problems in one unit.  However, while providing all these features in one box at a reasonable price, the firmware in many boxes is buggy and can prove frustrating for some users.  In addition they lack the full features of firewalls or more mature router products.

Most of the information presented on this page was obtained from www.dslreports.com, an excellent source for DSL information, tools and tests.  I highly recommend this site.