I'm still quite new to the Testmy.net community, but this appears to be a question asked frequently, "Why is my DSL connection not as fast as advertised?" Here's my answer...
DSL (Digital Subscriber Line) is an interesting technology which allows broadband internet via your telephone lines. This technology occupies the upper frequency bands of the phone system (32Khz~1.1Mhz) and because this is not true digital, but a system that really runs via an analogue network, it is subject to interference from all kinds of sources (AM Radio anyone?) that this can cause odd results during speed tests, as well as when playing online multiplayer games.
This type of service is dependant on your distance from the telco central office (CO) and alot of people do not understand this, and spend alot of time getting angry and frustrated because their speed is not exactly what is posted on the ISP website. A closer look shows us that any ISP uses an "Up To" phrase to communicate speeds, ie: up to 3Mbit.
In the case of a DSL provider, if you are more than 3200 meters (3.2KM) from a telco facility, your speeds will be reduced, and you may be placed on an interleaved profile (more on interleave further down) This is all done to help keep the consistency of your service constant, and if we do change your speed profile to something higher, it will degrade the quality of service delivered to you, including slower speeds, frequent losses of communication (Synch) and even total loss of use!
The closer you are to a central office, the better your DSL connection will be, but these are not the only factors involved. Obstacles to the signal are scattered around the telephone network, such as load coils, which can pretty much destroy a DSL signal. In the case of a load coil, they are required to keep voice services running reliably, and no telco will remove them just so you can get DSL, as this would cause voice disruptions to everyone else on that loop!
If you are further than 3.2KM on the wire from the CO (not line of sight) then you will most likely be placed on an interleaved profile, which allows for better error checking and correction to be done, and therefore helping to maintain your speed, but there is a downside, you will never see ping times under 60ms. For most applications this is perfectly fine, and you will never even know that you are on interleaved most of the time. However, if you are a gamer, you will see in-game latency jump all over the place and probably not get the same kind of results as you would with a cable connection.
To determine what type of profile you are on, you can always call and ask one of the technical support agents for your ISP, but this does not always answer the question, as there are agents who really don't understand the difference, and don't understand what you're asking for. If you encounter this, ask them to read you the profile name, most DSL isp's have specially formatted profile names to indicate whether it is interleaved or not. As I work for Bell Canada, on Sympatico if you are on an interleaved profile your profile name will begin with "al2" and "al1" for FAST channel.
Example: Interleaved: al2_d3008_3008_256_u800_800_256
(These examples are Bell Sympatico profile names for a 3Mbit connection)
Typical Downstream Speeds
1Mbit = 1184Kbps
1.5Mbit = 1728Kbps
3Mbit = 3008Kbps
3.5Mbit = 3488Kbps
4Mbit = 4032Kbps
5Mbit = 5056Kbps
This is by no means a complete explaination, but due to the sheer number of questions that have been asked of myself and others, this is the beginning of a complete explaination DSL technology and your speed to the internet.