DSL and VDSL internet runs over the old telephone line and has two traits that confuse people: the upload tends to be much slower than the download, and two neighbors can have completely different speeds. Let us explain why that is and what DSL speed really depends on.

What DSL and VDSL are

DSL is internet over a metallic telephone line, that is over the copper pair that runs to the house. The older and slower variant is ADSL, the newer and faster one is VDSL. The internet runs alongside the ordinary telephone on higher frequencies, so both work at the same time. While fiber carries data with light, DSL is bound by the physical limits of copper.

Why the upload is slower than the download

This is not a fault, but a deliberate design. The letter A in ADSL stands for asymmetric. The available frequency band on the line is divided unevenly: a larger part is reserved for downloading and a smaller part for uploading. It comes from the fact that an ordinary user downloads (web, videos) far more than they upload. That is why you see plans like 50 Mbit down and only 5 Mbit up. VDSL is asymmetric too, just with higher numbers.

What DSL speed depends on

DSL speed is not given only by the plan, but mainly by the physics of the line:

  • Distance from the exchange or cabinet. This is the most important. A signal over copper weakens with length (this is called attenuation), so the further you are, the lower the speed. VDSL uses higher frequencies that weaken even faster, so it is very sensitive to distance.
  • The quality and condition of the line. Old, oxidized or badly joined wires lower the speed.
  • Interference from adjacent lines. In one cable bundle the lines interfere with each other (crosstalk).
  • The technology used. ADSL, VDSL and VDSL2 with vectoring differ significantly in maximum speed.

Why two neighbors have different speeds

Precisely because the length and quality of the specific line to the exchange decide. Even two neighbors can be connected by lines of different lengths or different ages, so one has full speed and the other significantly lower, even though they have the same plan.

What to do about a slow upload

If you need a higher upload, for example for cloud backups, video calls, working from home or sending from cameras, DSL will limit you. The real solution is a fiber connection, which tends to be symmetric (the same download and upload). Check whether fiber is available in your area, or consider LTE or Starlink. You will find more on speeds in the article internet speed.

Dealing with slow internet and not sure where the problem is? Get in touch, we will measure the line and advise the best solution for your location.