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What’s the difference between DSL, ADSL and VDSL?

We will explain the key features of ADSL and VDSL connections in comparison to the more general term of DSL.

DSL means “Digital Subscriber Line” and is a term for several similarly structured data transmission types. Over the years, DSL has further developed into multiple variants with the main differences being achievable transmission speeds and ranges. The two main variants in Germany are ADSL and its successor VDSL with the latter being the faster of the two.
Despite this, both ADSL and VDSL have made separate developments in range and speed which can be identified by the suffix “Annex”. For example, the first DSL connections in Germany were mostly ADSL Annex B, followed by ADSL Annex J and most recently VDSL Annex Q known as “supervectoring”.

Simply put, the higher the letter after “Annex” the higher the internet speeds.  
The following table shows the maximum transmission speeds of each DSL technology.

All figures in Mbps.

DSL Technology Download Upload
ADSL Annex B 16 1
ADSL Annex J 16 2.8
VDSL 50 10
VDSL Vectoring 100 40
VDSL Supervectoring (Annex Q) 250 40


ADSL stands for “Asymmetric Digital Subscriber Line” with “asymmetric” signifying the fact that transmission speed will differ depending on direction. In the direction of reception, to you ("downstream"), transmission rates of up to 16,000 kbit/s (approx. 16 Mbit/s) are possible. In the direction of transmission ("upstream"), i.e. from you to the Internet, up to 1152 kbit/s (approx. 1 Mbit/s) are achieved.
ADSL utilises the classic copper lines of the existing telephone network for data transmission. In the past, this had great advantages as no new lines had to be laid and technological improvements could be made simply within the switch box. Compared with telephone modems (up to 56 kbit/s) and ISDN connections (with two bundled channels of 64 kbit/s each), the data rate could thus be increased enormously with comparatively little effort.
An important further development of ADSL is ADSL2+ (Extended bandwidth Asymmetric Digital Subscriber Line 2), which theoretically allows up to 24 Mbit/s downstream.

With the first ADSL connections with the addition of Annex B, it was still possible to operate traditional analog telephony in parallel with digital data transmission. To do this, the signal simply had to be split between the modem and the telephone using a splitter. With the introduction of Annex J as standard, this was no longer possible. Although connections with Annex J are faster, the areas of the signal previously reserved for analog telephony were now also utilised for data transmission. Due to this, calls are nowadays are mostly made over the internet seeing the rise of Voice over IP (VoIP).


VDSL stands for “Very High Speed Digital Subscriber Line,” which increases data transmission speed yet again by harnessing technologies such as vectoring and supervectoring.  
The background to this development was that copper cables experience relatively high signal lose which negative impacts on signal quality. As a result, the maximum Internet speed drops rapidly over long distances.  
To get around this problem, VDSL uses modern fiber optic cables to cover long distances. This allows data to reach a distributor near the customer at high speed. Only the last few meters to the household are still covered by the old copper cables.
With basic VDSL, user can expect speeds up to 50 Mbit/s in the direction of reception, ie downstream. However, by using vectoring and supervectoring, this can be increased to up to 100 Mbit/s and 250 Mbit/s respectively.

What do I need?

If you are interested in such a VDSL upgrade, please make sure that your router is compatible with VDSL, vectoring or supervectoring. You can use our router-check for this or simply by contacting the manufacturer. From years of experience, we recommend the routers of the "FRITZ!Box" series from AVM, which you can rent or buy from us at a reasonable price.

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