Fiber to the X - The architecture of fiber-optic lines

Fast, reliable, high-speed Internet is an important prerequisite for meeting the digital demands of tomorrow. That’s why Deutsche Telekom is investing billions of euros every year in building out its fiber-optic network – so people everywhere in Germany can benefit from fast internet connections and high bandwidths.

Fast, reliable, high-speed internet is an important prerequisite for meeting the digital demands of tomorrow.

Fast, reliable, high-speed internet is an important prerequisite for meeting the digital demands of tomorrow. © Deutsche Telekom

The broadband network in Germany is already very well developed: Deutsche Telekom alone has expanded its fiber-optic network to a total length of more than 750,000 kilometers in the interim. And the network grows larger every day. That’s why more and more households that are still using DSL to surf the World Wide Web are getting direct optical fiber to the home connections. 

FTTH – Fiber To The Home

FTTH stands for “fiber to the home”, meaning all the way to the house or apartment. An FTTH line is a direct link from the home connection to the global fiber-optic network and enables download speeds of up to 1,000 megabits per second. DSL lines based on copper wires can only achieve download speeds of around 16 megabits per second. VDSL, a combination of optical fiber and copper wires, enables speeds of up to 50 megabits per second. The additional vectoring technology makes transmission speeds of up to 250 Mbit/s possible. 

Segments of a fiber-optic network

An internet line is made up of different components. Telecommunication providers like Deutsche Telekom are building out their broadband networks in cities and communities. Nowadays, fiber-optic cables are used almost exclusively for the expansion of these networks. The lines pass through multiple nodes on the way to the user. The fiber-optic network consists of the following segments:

  • Core network
  • Exchange
  • Street cabinet
  • Outside plant termination point
  • Telephone socket
  • Device

In the interim, as digitalization and the ongoing build-out with fiber-optic cables continues to advance, nearly all Deutsche Telekom exchanges are now connected with the core network via optical fiber. An exchange like this is a node in a local network, where signals are converted if needed and forwarded to the subscriber lines. From here, the fiber optic lines run to a street cabinet, which could be located at the side of the road in a residential area, for example. You’ve probably seen these gray cabinets in your neighborhood before.

From these street cabinets, which are usually located near edifices, the optical fibers of an FTTH line lead to the surrounding buildings, which can be residential or contain offices and stores. Under the vectoring technology, the line to the building is made of copper wire. Each of these properties has an outside plant termination point, which is where the telecommunication provider’s network line ends and connects with the network inside the building. It is the starting point for distributing the lines to individual phone sockets within the homes or office units. The subscriber line terminates in the wall socket where the respective device is connected, such as a phone or WiFi router.

The architecture of a fiber-optic line

How the internet gets to customers has changed drastically over time, due to new technologies and possibilities. When the World Wide Web started to take its first baby steps, copper wires were the primary foundation for the classic landline network. Under this approach, the data is transmitted over end-to-end copper wires. Consumers surfed the web based on ISDN (Integrated Services Digital Network).

When the optical fiber build-out began, more and more fiber-optic line architectures were added to the copper wires, enabling much higher bandwidths for data transmission. At its core, the upgrade of the optical fiber network is marked by the installation of new fiber-optic cables, which are increasingly replacing copper wires for the transmission of data. This does not mean that high-speed lines already consist solely of fiber-optic cables, however. Instead, a broadband network contains segments of optical fiber that continue to be supplemented with electroconductive copper wires. As the optical fiber build-out continues, the share of copper wires in the network is declining. 

The basic principle of the network architecture on the last mile is “fiber to the X”, where “X” stands for the termination point of the fiber-optic cable. In colloquial terms, the “last mile” describes the path from the exchange to the subscriber line. The design of this last mile can vary in a broadband network. The FTTx principle describes the following termination points:

The last letter, X, indicates the exact demarcation point between an optical broadband line and the house wiring, which is often still made up of copper wires. It is this data junction where technical instruments (OLTs – optical line transmitters) convert the optical signals into electrical impulses.

Differentiation between broadband networks

Fiber to the home (FTTH) is a network architecture under which the optical fibers are laid to the home or office. In other words, under FTTH, the fiber optic cable ends at the socket on the wall in the home or business. An FTTH line is essentially the best possible kind of broadband connection. Under all other connection versions, the maximum performance and speed of the broadband lines are reduced due to the copper components in the house wiring. That’s why Deutsche Telekom prefers the benefits of FTTH networks in new optical fiber build-out areas.

Fiber to the curb (FTTC) is a broadband connection variant under which the fiber-optical cables are laid to the street cabinet on the sidewalk. From here, the section to the wall socket still consists of copper wire. Consumers can only enjoy the internet at VDSL speeds under this connection type. The conversion of optical to electrical signals is performed in the familiar gray cabinets at the side of the road.

In the fiber to the building (FTTB) approach, a fiber-optic cable is laid to the building and ends at or close to the outside plant termination point. Within the building, the final segment, from the outside plant termination point to the home or office, is bridged with copper wire.

Fiber-optic networks are the future technology for more digitalization

The installation of optical fiber has both advantages and disadvantages compared to the existing copper wires. 
Optical fibers reduce data transmission losses, even over longer distances. This means customers can take advantage of the full bandwidth that optical fiber makes possible. No other kind of cable guarantees better bandwidths. 

Thanks to the high bandwidths of a fiber-optic-powered internet connection, users benefit from the advantages of fast data transmission at all times. A key advantage is the ability to run multiple online applications in parallel without any noticeable loss in transmission speeds. In a single-family home, it lets the parents watch a streamed movie on the couch, for example, while the children can dive into the world of real-time online gaming with their friends. A fast fiber-optic line is also an excellent foundation for connected homes with smart home systems, which make our lives safer, more convenient, and more efficient in a variety of ways. 

One characteristic of fiber-optic cable is that it does not transmit electricity.  As a result, alarm systems and emergency call services require an emergency power supply, as well as possibly a secondary transmission channel via mobile communications or copper wires. 

The costs of the broadband build-out in Germany amount to tens of billions of euros in total. The optical fiber build-out is in full swing, because broadband internet is a crucial future technology. Deutsche Telekom alone is investing around 5.7 billion euros in its networks in Germany every year. The government has announced its objective of driving the digitalization of society forward, with broadband connections as a key ingredient. As such, incentives are being provided to intensify the installation of fiber-optic networks in rural regions.



DT invests several billion euros every year in building networks.