ADSL2 and VDSL

Between all the abbreviations and a wide variety of technologies for high-speed internet connections, it is easy for an ordinary user to lose their way. Let's look at how the technologies for connecting to the internet over telephone lines differ, and what advantages the two most common standards offer?

Internet providers offer various types of internet connection. The most common on the Czech market are VDSL and ADSL technologies, which use telephone networks and therefore cover the vast majority of places in the Czech Republic. The abbreviation DSL stands for Digital Subscriber Line (in Czech, “digitální uživatelská linka”).

ADSL, together with VDSL, is most often used in places where other ways of connecting are problematic or where there is no affordable alternative. Thanks to the use of the existing telephone network, it is not necessary to bring a new line to the customer

A modem is essential for receiving an ADSL and VDSL signal, as it processes the signals between your computer and the telephone connection. Modems are usually rented or sold outright to end customers by internet providers. These devices often also combine the functions of a WiFi router and a network hub. This makes it easy to set up a home wireless network without needing to invest in additional equipment.

ADSL - internet connection via telephone lines

ADSL, or Asymmetric Digital Subscriber Line, is a so-called asymmetric digital line. The name of the technology itself refers to the characteristic of this connection to offer a higher speed for downloading data towards the user (download) and a lower one for sending data from the user (upload). In contrast to so-called symmetric lines, where the speed can be the same in both directions, the difference between download and upload speeds is often striking with ADSL.

Today's ADSL2 and ADSL2+ technologies offer connection speeds of up to 28 Mbps for downstream and around 3.5 Mbps for downstream. In practice, this full speed is rarely achieved. The quality of an ADSL connection is indeed significantly affected by the distance from the exchange and the quality of the wiring.

The further the customer is from the exchange, the lower the quality of the connection and the speed will drop. A customer more than 3 km from the exchange may achieve speeds of only around 5 Mbps or less on a package labelled “up to 20 Mbps”, for example. By contrast, a household 500 metres from the exchange may achieve download speeds of around 18 Mbps on the same package.

The key word here is “up to”. For the reasons mentioned above, operators prefer not to guarantee a fixed speed for ADSL and VDSL connections, and only mention in their offers that this speed may be achieved under certain conditions. In general, up to a distance of 3.5 km, ADSL2/2+ offers better connection speeds than ADSL. Beyond 4 km from the exchange, the difference between the individual versions of the technology is minimal.

VDSL - faster connection with potential for further speed increases

While ADSL has already reached its speed limits, VDSL has speed literally in its name. It is in fact an abbreviation for Very High Bit Rate Digital Subscriber Line (alternatively Very High Speed DSL – very fast DSL). Currently, VDSL version 2 is often used, although operators' offers often show it without a number for simplicity.

A symmetric VDSL connection offers theoretical speeds of up to 100 Mbps for both download and upload. In practice, the most common packages are those offering “up to 20 Mbps” upstream and “40 Mbps” downstream.

Most operators have no problem providing existing customers with an upgrade from ADSL to VDSL while keeping the same pricing terms. However, the service must be available in the given area. As with ADSL, VDSL is also sensitive to distance from the distribution point, and at longer distances, specifically beyond 1.3 km, the speed advantages of VDSL are lost. In such cases, operators do not even offer VDSL and offer only ADSL.

Comparison of VDSL and ADSL

Distance from the exchange affects connection speed

Operators often promise speeds in their offers that are not actually achievable at the connection location. Why is that? With VDSL and ADSL technologies, the distance from the exchange negatively affects connection parameters. In general, losses are minimal up to 300 metres, after which signal quality drops rapidly.

How to find out the connection speed at your place of residence?

Operators provide forms on their websites which, after you enter your address and telephone number, pass your details on to a sales representative, who will contact you with a more specific offer. It is important here not to settle for the theoretical “up to 20 Mbps” figure, but to ask the operator to specify the speed at your location, or to ask how far you are from the nearest exchange. Then you can simply look at the chart above.

You do not need to take out a landline for ADSL and VDSL

Initially, ADSL was closely tied to packages that included calls over a landline, but over time this changed and so-called “bare ADSL” emerged. Thanks to it, prices fell significantly and the connection became available to an ordinary customer.

Are modems compatible with ADSL/VDSL?

Older modems designed for ADSL usually cannot cope with VDSL. When switching to a VDSL connection, you need to buy a new modem. The connection provider itself often offers it for purchase or rent. By contrast, modern VDSL modems often also support ADSL, ADSL2 and ADSL2+.

What is connection aggregation?

Operators often state connection speeds in their offers together with a mention of so-called aggregation (grouping). This refers to sharing the line with other users in your area. So if you see a 1:4 aggregation for a 20 Mbps connection and you are connected at the same time as other users, your speed may drop to 5 Mbps or lower.