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ADSL: What It Is, How It Works And What Are The Other Transmission Technologies

ADSL is one of the data transmission technologies through which the Internet can be accessed. In this guide, we examine the characteristics of the leading technologies available to domestic users, starting with the most widespread, ADSL, and then analyzing other more recent ones such as optical fiber and satellite connection.

Data Transmission Technologies


ADSL( Asymmetric Digital Subscriber Line) is a technology that allows the transmission of data for connection to the Internet using the traditional telephone twisted pair. Using the twisted pair, already installed in most homes, represents an advantage for this type of technology and partly explains its diffusion: those who intend to use ADSL are not required to install any additional equipment if they already have a standard telephone line. He will have to equip himself with an ADSL modem, but this is a modest expense.

ADSL is defined as asymmetrical because different speeds characterize it in upload(i.e. in the data transmission phase) and download(i.e. in the data reception phase). For residential connections, higher transmission bandwidth is dedicated to the download flow than the upload. This is because the typical activities of user navigation require more network resources to download, for example, when browsing a website with several images or downloading huge videos and movies. The upload speed is lower, but it is still essential to determine the internet connection quality. If the upload bandwidth is “saturated”, i.e. it is wholly occupied, and even the download of a file could be affected, as, during the download process, the computer must send data packets to the remote server to which it is connected.

The upload speed is critical when using peer-to-peer systems, in which the connected computers continuously send and receive data streams between them. The speed of ADSL technology can vary considerably from one operator to another and according to the rate chosen. The standard speed at this time is equal to 7 Mbps in download and 384 Kbps in upload but can reach up to 20 Mbps in download and 1 Mbps in upload. In particular, we talk about:

  • ADSL2, which reaches a speed of 12 Mbit / s in download and 3.5 Mbit / s in upload;
  • ADSL2 + gets a rate of 24 Mbit / s in download and 1.5 Mbit / s in upload.

However, it must be borne in mind that the actual speed of the ADSL connection and network browsing is impacted by several factors, some of which may be dependent on the user’s access point, such as:

  • The type of modem and computer
  • The number of applications opens simultaneously on the computer
  • The navigation browser

Others, on the other hand, are linked to the infrastructure that connects the user to the network:

  • The clogging of network traffic
  • The quality of the data cables
  • The distance from the telephone exchange

This determines the difference that is almost always present between the real speed(the actual internet access speed) and the nominal speed (the one declared contractually by the operator providing internet access).

Optic Fiber

Optical fiber is a data transmission technology that uses small glass fiber cables instead of the traditional telephone twisted pair or plastic polymers that allow the propagation of optical signals. The main advantages of optical fiber compared to the standard copper pair are the following:

  • Large bandwidth capacity, which allows effective data transport and coverage of long distances.
  • good resistance to electromagnetic disturbances, radio frequencies or climatic conditions (such as temperature variations).
  • Good flexibility and resistance of the cables facilitate installation and guarantee less possible failure.

Thanks to these features, a fiber optic internet connection allows download transmission speeds from 10 Mbps up to 100 Mbps and an upload speed from 1 Mbps up to 3 Mbps. These are the current speeds provided in the contracts dedicated to domestic customers. The optical fiber could potentially reach higher speeds (1024 Mbps, or 1 Gbps). There are two ways of connecting to a fiber network: FTTS and FTTH.

  • FTTS (or Fiber to the Street): defines those connections in which the optical fiber from the control unit reaches the cabinet (the proximity control unit near the user’s home), and the twisted pair is used from the cabinet to the user’s home in copper ( for a length of fewer than 250 meters).
  • FTTH (or Fiber to the Home): indicates those connections in which both sections (from the control unit to the user’s home) are made via optical fiber.

The main disadvantage is represented by the significant installation and cabling costs and by the network coverage, which is currently limited to larger cities such as, for example, Milan, Genoa, Turin, Bari, Naples, Rome and Bologna. However, the evolution of fiber is a topic of interest for all the leading telecommunications operators, which offer increasingly advantageous offers and are investing to extend the geographical coverage of their internet access services.


The spread of telecommunication services dedicated to domestic users, particularly internet access, has developed over the last ten years. These services allow you to access the Internet via artificial satellites in earth orbit through the following two types of connection:

  • One-way connection: download traffic takes place via satellite connection. Upload traffic takes place over the telephone network with a traditional 56k modem. This is a solution that is no longer practiced, which requires at the same time a double connection (and therefore double costs) to the satellite and the 56kb line.
  • Bidirectional connection: download and upload traffic take place via satellite. The user only needs to have a satellite dish and a satellite modem. No telephone or cable connections are required, nor any additional software installed on the PC. The modem is usually made available by the service provider.

One of the main advantages of these services is the fact that they are accessible almost everywhere, even in the most isolated areas, becoming a possible solution to bridge the digital divide: the satellite connection is a valid alternative to access the Internet in those areas where standard telephone lines are not available. Furthermore, thanks to the evolution of digital transmission systems, satellite network use is no longer associated with high costs. In terms of price and speed, it is comparable to traditional broadband technologies such as ADSL and Optical Fiber, as it can guarantee a bidirectional connection with a download speed of up to 20 MB and an upload speed of up to 6 MB. One of the significant constraints of this technology is the latency time of the satellite network, which is greater than traditional cable technologies.

Which Modem Is Best For You

What Is The Modem?

The modem is an electronic device that allows you to “modulate”, that is, to regulate a signal so that it can be transmitted along the traditional telephone line; then the modem “demodulates”, that is, it transforms again the signal coming from the telephone line. From a standard speed of 56 Kbps, in a few years, the technological evolution of the ADSL modem has made it possible to reach a download speed of up to 20 Mbps and an upload speed of up to 3 Mbps. The ADSL modem connects to the computer through a USB network cable. However, the modem characterized by a wireless connection is increasingly common.

The Wi-Fi modem allows you to extend the Internet connection throughout the area covered by the network without using cables. Therefore, it is very functional, for example, in the case of laptops, tablets or smartphones. Generally, the ADSL modem with both network cables and Wi-Fi can either be included in the rate or provide for an optional cost per month that is different depending on whether you decide to buy it or use it on loan for use, or you can also decide to use a proprietary modem. However, in the latter case, it is necessary to comply with the technical characteristics required by the operator. Sometimes, to make the offers more attractive and to ensure good value for money, the modem is given as a gift as a temporary promotion.

Is A USB Modem Or A Router Better?

What are the limits of the modem? The modem may not be compatible with PCs or electronic devices in which a program from the same operator is not installed. This setting means that different users cannot use the same ADSL connection. Furthermore, suppose several devices are connected to a traditional modem through a USB port. In that case, both the modem’s operation and the devices’ performance could be lower and considerably slowed down.

The router, an electronic device that routes the signal between different networks, is ideal if you plan to connect more than one device to the network (for example, one or more computers, smartphones, or tablets). It can be set with the configuration for a single user, characterized by having all the ports open and in multi-user mode that allows you to connect multiple devices to the same network. In addition, the router ensures superior security for the web, as it will enable you to configure and filter the input ports.