Network level (cable television)

from Wikipedia, the free encyclopedia

The network levels ( NE for short ) are different sections of the cable television network .


When cable television was introduced in Germany, it was divided into different network levels. The decisive factors here were technical and economic criteria. The cable television networks of that time (also known as “broadband distribution networks” in the technical sense) were used to transmit radio and television programs from central distribution points to radio subscribers .

The expansion of a nationwide technical infrastructure for broadband distribution networks for cable television goes back to decisions made in the 1970s , in particular the recommendations of the Commission for the Expansion of Technical Communication Systems ( KtK ) from 1976 .

Cable television requires a tree-like network structure ; H. a network that branches out from one point. The broadband distribution networks were built using copper coaxial cable technology, as this technology enabled the most economically sensible requirement to be met at the beginning of the cabling. Depending on the design, the bandwidth of this copper coaxial cable currently ranges from 450 MHz to 1 GHz.

When the cable network was designed, the network was technically separated into four levels. When classifying the network levels, the generation of the signal in the direction of the end recipient is counted.

In simple terms, the cable network works by producing program content from the broadcasters / television studios and routing it to the central receiving points of a cable network, the so-called cable headends. At the beginning of the 1980s, this was mainly done terrestrially (i.e. by means of antennas). Today this form of transmission has become rare: Most broadcasters have rented so-called transponder spaces on radio satellites and send their radio programs directly via an uplink to the satellite and thus to the headend. This is network level 1 .

The network level 2 consists of the cable headends, originally from the national distribution level, which TV towers was covered. This is where the signals are received and processed and then distributed to the local networks. The end of this network level is actually formed by smaller distribution stations that supply a city district.

It was only here that network level 3 officially began , from where it took over the distribution of radio signals through the streets and front gardens into the houses. Today the term "network level 3" has expanded to include all regional signaling, i. H. from the headend to the house connection. In the cable business, network levels 1 and 2, as independent terms, only play a subordinate role. The following is based on the current terminology.

Levels 1, 2 and 3 were originally assigned exclusively to the broadcasters and the Deutsche Bundespost and were financed with public funds, while network level 4 ( house distribution systems ) was installed and operated by private companies. Local cable television providers or housing associations can operate systems on their own in network level 4 and also feed their own programs or additional channels into the cable network there. In Germany, for cable television, you are usually a customer of a level 3 provider.

The network structure of the cable television network can be represented as follows:

  • Network level 1
    TV and radio studios and the way to the broadcasting station.
  • Network level 2 - Central facilities
    Distribution channels via
    radio transmitters , satellites , directional radio .
  • Network level 3 - The actual broadband distribution network with active and passive components
    1. Cable headends or radio reception centers (bundling of programs) for feeding into the
    2. Cable television network, i.e. the distribution network (e.g. in municipal streets and paths) to private households, residential complexes or housing associations up to the property line or the house transfer point .
  • Network level 4 - Connected house transfer points with the private house distribution networks behind them

In the course of the establishment of the cable networks in Germany, the establishment of different network levels and their separation in terms of ownership structure and technical responsibility was decreed, which is a unique process worldwide. From a technical point of view, the separation between the upstream network level 3 (usually distribution in a local network) and network level 4 is not necessary, but was decreed by the then responsible Minister of Post, Christian Schwarz-Schilling . The argument was that the monopoly of the Deutsche Bundespost over the regional networks - unlike, for example, the telephone networks - should not extend to the direct relationship with the users. Therefore, the expansion of the cable routes in the buildings should be left to private companies in order to strengthen the middle class .

What was not openly stated here was the rapidly emerging technical development that in the foreseeable future would no longer allow the cable TV networks to function only as carriers of radio and television coverage, but would also make them attractive as a medium for communication services. From experience in the USA and Switzerland, it was clear to those in the know that traditional telecommunications services such as internet and telephony could also be offered via TV cable and that a direct and nationwide competitor to Deutsche Telekom would have arisen in one fell swoop with the sale of the BK network which of course was not in the interests of Telekom. The politically intentional retention of the fragmentation of the network levels was a possible and then committed solution. With its own telephone network, on the other hand, Telekom has retained all network levels and saved the line sovereignty resulting from the telecommunications monopoly up to the end customer even when the telecommunications market was deregulated, even if it had to open it physically and electronically under massive regulatory requirements.

Network level 1

Put simply, the network works by producing program content from the broadcasters / television studios and feeding it to the central receiving points of a cable network, the so-called cable headends or playout centers . At the beginning of the 1980s, this was mainly done terrestrially (i.e. by means of antennas). Today this form of transmission has become rare: Most broadcasters have rented so-called transponder spaces on satellites and send their programs directly via an uplink to the satellite and thus to the receiving station. This is network level 1.

Network level 2

Network level 2 consists of the cable headends or playout centers , originally also from the supra-regional distribution level, which was covered by television towers. This is where the signals are received and processed and then distributed to the local networks.

Network level 3

The level 3 ( NE 3 ) is in today's parlance, the term for regional broadband cable networks , especially from branch cable and main cable , outgoing existing networks by the main distributors on the street cabinet , within towns the signals and distribute to the private land route.

Network hierarchy

The network layer 3 is divided into various sub-layers: The conventional arrangement provides the cable headend (in technical jargon: Parent BK-repeater station / Conv) from strong wires of coaxial cable before, which are guided to the neighborhood and in so-called user-side BK amplifier points / end bBK. From there, a tree structure of previously pure copper cables in a coaxial structure - now also fiber optic cables - connects to the amplifier points ( VrP ) in the local network, which in turn is divided:

A-lines and B-lines ensure onward transport within the district

C-lines supply streets and run along the street (mostly on the side of the road)

D lines are the outgoing connections that supply individual houses.

On these long stretches it is necessary to repeatedly amplify the transported signal, especially if there is a branch to the next distribution level. The most conspicuous appearance of this necessity are the street distributors, also known as reinforcement points, which appear as gray boxes on the sidewalks. The failure of entire streets or city districts is often due to road users ramming these boxes and breaking the cable connection. The same thing happens through vandalism at these booster points. Since 230 V is supplied to the so-called feed-in points in the cable network for operation by the local energy supplier, a failure of this power supply is a failure of the signal. During road construction work it has also happened again and again that lines were cut by excavators and thousands of screens remained black as a result.

The network termination is the transfer point (ÜP) where the connection to the house network is established. The transfer point is the last element of network level 3 and is therefore the property of the respective operator. In general, it is a small, inconspicuous box that is placed in the basement of the house. The subsequent house network is referred to as network level 4 .

Network upgrade and ring structure

In the nineties, network level 3 was initially rebuilt on a project-by-project basis, and from 2000 onwards, its topology was also extensively rebuilt. Instead of the hierarchically organized tree network, rings made of fiber optic cables were placed between the feed-in stations ( playout center ) . Regional rings cover a large area with a catchment area of ​​millions of participants. These can forward the received signals over a large area in both directions from a central network node. The cable headends connected via such a ring thus become subordinate network nodes and no longer require their own receiving devices. Further fiber optic rings branch off from these stations, replacing the old coaxial lines and connecting the nodes of the individual districts with one another. In order to optimize the data transport in the direction of the subscribers, fiber optic stub lines are laid behind them up to the street distributors, in which the fiber optic link ends and the transition to the existing coaxial network is established. These junctions are called fiber optic nodes, or fiber nodes. There are usually between 1,500 and 6,000 residential units to be supplied behind a fiber optic node. This means that the gray boxes on the sidewalks have become an important part of the multimedia supply.

This structure results in two main advantages:

  • The susceptibility to failure is reduced to a minimum. If a fiber optic ring is damaged, the signal can simply take the opposite path and is no longer interrupted. This drastically reduces signal failures. This only applies to the incoming connections, not in the local network.
  • The fact that signals are transported in two directions has turned the unidirectional distribution network into a bidirectional multimedia network that new applications can use to run: This makes it possible to offer all services that require data transport in two directions, for example telephone services and Internet services .
  • The performance of the glass fiber allows a much larger range of programs and services. The number of assignable channels doubles.

When an area in North Rhine-Westphalia with one million serviceable participating households was converted to this structure between 2000 and 2002, problems also became clear:

  • The change initially led to technical problems such as picture and sound failures, which could only be completely turned off after weeks.
  • The investment in such measures was so capital-intensive that in 2002 these measures were not expanded. The network operator had meanwhile got into a financing crisis. However, it was later continued by Unitymedia .

Business models

For a long time there was a monopoly of the Deutsche Bundespost in network level 3 , which Deutsche Telekom took over. Those who wanted to use cable television turned to the monopoly operator and used the connection for a monthly fee. The only alternatives were the classic terrestrial reception via room or house antenna with a correspondingly limited range or via satellite reception, which in many cases is still not permitted by the landlord today. The cable usage charges were and are still today based on quantity scales, i. This means that the fee per participant decreases the more of them are connected to the same transfer point.

In individual cases, commercial operators had the opportunity to apply for a so-called “higher-quality ÜP”, which does not end after the D line, but in the street. Due to its higher performance, entire new development areas could be connected behind this, so that the private cable companies built large sections of network level 3 on their own and built monopolies in city quarters.

In the areas in which new applications are offered today, the market is in motion: Internet services via cable are superior to the telephone-based Internet and, due to the distribution medium "coaxial cable", are physically much more powerful than 2-wire telephone cabling. On the other hand, in Germany (in contrast to the rest of the world), fast Internet is conceptually equated with DSL and Internet via TV cable is not also considered. In addition to the massive advertising for DSL, it was also the obstruction of competition by Telekom that deliberately politically wanted to maintain the fragmentation of the network levels resulting from the development phase of the network in order to keep a newly emerging competitor small. Even if this was justified with "preventing a television monopoly", it was clear to the initiated through experience from the USA and Switzerland that the classic telecom services Internet and telephony can also be offered via TV cable and here at one stroke Sale of the BK network would have created a direct and comprehensive competitor to the classic Telekom, which of course was not in the interests of Telekom.

In order to be able to use the new services, the subscriber not only needs a cable modem , but also the corresponding technical capabilities of the house networks, which are often owned by other operators (see also the article network level 4 ). Only when the operators of network levels 3 and 4 agree on the transmission of Internet services and the technical investments are made, the user can receive Internet. This service is offered by the operator of network level 3, so that a double customer relationship arises. Permits with and without compensation payments between the network operators involved are possible.

Operator and recent development

When in 1999 , under pressure from the EU, Telekom spun off its cable business and later sold it to investors , it initially founded the subsidiary Kabel Deutschland GmbH (KDG) , which divided its business into several regions. The regions of Baden-Württemberg, later Kabel BW , North Rhine-Westphalia (initially trading as Kabel-NRW, later ish ), and Hesse, initially trading as iesy, were sold . The remaining regions kept the name Kabel Deutschland and were only sold to a private consortium in 2002. In the summer of 2005, Ish and Iesy merged and this resulted in Unitymedia . Kabel BW was added on July 1, 2012. In the meantime planned re-mergers or takeovers of large operators of network level 4 were prevented, so that today two large operators operate regional networks. The modernization status of the cable networks was quite different. The success of the new applications has largely fallen short of expectations, as the agreement with the operators of network level 3 on business models is complicated. The broadband company of Robert Bosch GmbH in particular relies on its own development of regional networks in order to use the entire added value of the cable business for itself. The acquisition of large housing companies, whose number of residential units makes economic operation more likely, plays a key role here. The larger NE4 operators Telecolumbus, ewt and Primacom joined forces in September 2006.

Network level 4

House transfer point up to 862 MHz from Astro

The level 4 (NE4, home network) refers to the part of the broadband cable network is built for signal transmission within the land and buildings. Because of this property, network level 4 is also described as the “last mile” to the customer, i.e. the user of the cable connection .

Network hierarchy

Network level 4 begins at the defined network termination of level 3, which is called the house transfer point (HÜP) or transfer point (ÜP). This is usually in the form of a cable connector housing attached to the wall in the basement or on the outer facade of the building to be supplied. It finishes with the antenna sockets in the supplied apartments. The operators differentiate network level 4 again into different parts:

Network level 4a: The feed from the HÜP to the house amplifier in the distribution box. The supply lines branch off from there. The signal is i. d. R. reinforced.

Network level 4b: The section from the distribution box to the apartments. Here the signal is distributed within the property.

Network level 4c: The cabling within the apartment that terminates in one or more junction boxes.

Network architecture

Since the cable network was originally only intended for radio reception (unidirectional network), the cabling was accordingly simple. The first cable networks were simply pulled through the apartments and each received an antenna output, with which the signal was practically "looped through". In essence, the so-called tree structure is similar, which was installed through an access path and only had branches in front of the apartments. The main problem with these architectures is their susceptibility to interference: in the event of a signal interference, all of the following apartments are disturbed in their reception and the cause of the interference is difficult to localize. In the 1980s, the existing terrestrial antenna systems were often converted and switched to cables. The old coaxial cables, distributors and antenna sockets were preserved. Only the supply line from the house transfer point and the amplifier were renewed.

Over time, the star network has increasingly prevailed. This is characterized by the fact that an individual cable is already installed in the distribution box for each residential unit and is routed into the apartment without interference with other supply lines. This largely prevents disruptions. In addition, an effective remedy against black users is created with individual cabling: Those who do not pay their cable fees can now be excluded from the service, which is only possible with a tree structure at the price that all units behind them no longer receive a signal.


Since network level 4 is at the back of the network hierarchy, its technical performance was always determined by the upstream networks. With the expansion of the bandwidth, which was initially limited to three television channels and radio frequencies, the house networks first had to be upgraded to 300, then to 450 MHz in order to be able to transmit the newly created broadcasting slots. In modern networks today a transmission capacity of up to 862 MHz is secured.

Another expansion is digitization . Digital programs have been transmitted in cable networks in Germany since 1996. Originally, only a few channels, for example Premiere (now Sky Deutschland ), broadcast a digital program. In the meantime, however, there are significantly more digital TV channels than analog TV channels. Since August 2017, some transmission has only been in the DVB-C standard.

Since 2001 , larger areas have also been equipped with return channels, which for the first time allow bidirectional use with new applications (high-speed Internet). These can only be used if network level 4 is adapted to the extended options of network level 3: The return channel must also be set up in the house distributor. The return channel occupies frequencies in the range of the former television channels 2 to 4 (47 to 68 MHz), which have not been used for television since around 2005.

Ownership and network operation - business models

According to the German Civil Code , the cable network of a house is basically a part that is permanently connected to the building and is therefore the property of the house owner. If this cable connection wants to be used, he can connect to the in-house network at the transfer point and usually pays the operator of network level 3 (formerly Deutsche Bundespost , then Deutsche Telekom , now a private operator) a one-time connection fee and monthly usage fees. In most cases this affects owners of single-family houses, whose house installation often only consists of a connection cable to the junction box. In principle, every resident is entitled to use the cable in apartment buildings; if there is no house network, it can be individually connected to the house transfer point.

Owners of apartment buildings often anticipate this by pre-installing network level 4 for their house. As a result, he himself becomes a direct consumer of the signal and pays a tiered usage fee depending on the number of residential units served, which he can pass on to his tenants via the ancillary costs.

In many cases, however, the house networks are owned by specialized service providers (so-called NE4 operators). They conclude a supply agreement with the home owner, which transfers ownership of the home network to them and in return obliges them to maintain and bill the users. In this way, the owners are relieved of responsibility for broadcasting coverage.

Large housing associations have often taken the opposite path , which consciously want to be active in this field and therefore operate network level 4 themselves or through specially founded subsidiaries.

Since the professional operators of house networks, as well as individual customers or home owners, bill the operator of network level 3 according to price scales, it is often possible for them to obtain favorable conditions in the form of volume discounts, which lower the price per connection below the level that a small community would could achieve. The network operators also try to keep the number of supplied residential units behind a HÜP as large as possible (optimization) so that the quantity scales are more effective. Therefore, individual house networks are often merged within the property boundaries (clustering) and connected to a single HÜP. The resulting large systems are associated with high investments, as the signals often have to be amplified several times within the house system. Therefore, the pension agreements generally have terms of 10 years or more. However, since the costs for the signal transfer are considerable despite the quantity scales and have also increased significantly in recent years because the NE3 operators would like to have direct customer relationships, these NE4 operators are installing their own cable head-end stations more and more frequently and thus become the NE3 themselves by they connect their own NE4 networks across property boundaries.

After the market for NE4 operators was very fragmented for a long time and was dominated by specialist electrical companies, there has been a consolidation as a result, in which some companies have achieved a dominant position. Particularly noteworthy are Tele Columbus , ewt (merged with Bosch ) and Primacom (in which Orion Cable is now significantly involved), as well as some operators in larger cities who have also set up their own networks in the region. Telekom had also tried to secure this lucrative market for itself through its own subsidiary and therefore founded DeTeKabelService . This has now largely merged with the network level 3 operators.

The separation between network levels 3 and 4 has led to a market constellation that has mixed customer and competitive relationships: the operators of both levels are fighting for business relationships with users on the one hand, and they are also supplying each other with signals. On the one hand they fight together against competing types of supply (satellite reception and terrestrial), on the other hand they persistently try to compete for market shares and take over the other network level. It is currently estimated that two thirds of the cable market is held by NE4 suppliers and one third receives the signal directly from network level 3.

The separation of the network levels has a disadvantageous effect, particularly with new services such as Internet and telephony via cable: the economies of scale necessary for an attractively priced Internet or even telephony offer are often not achievable by smaller NE-4 operators. However, where the NE 4 then also operate the NE-3 itself, it works with its own offers, such as B. Tele Columbus , ewt or Cablesurf (the latter, especially with smaller network operators, partly as a franchise ). Strictly speaking, the NE-4 operator is then no longer one, i.e. H. the separation of the network levels is then removed there.

Operator and recent development

With the deregulation of the cable market, two thrusts have arisen, both of which are aimed at the unions of network levels 3 and 4: The network operators of level 3 are trying to conquer the last mile for themselves in order to gain customer access (example: takeover of Tele Columbus Süd-West by Kabel BW and the takeover of Kabel BW by Unitymedia). Occasionally, cooperations are also agreed between the operators, which regulate the transmission of internet services, for example. On the other hand, the NE4 operators are increasingly installing their own receiving stations (some with their own Internet services and telephony products) and thus expanding their network up to network level 3. This leads to the deregistration in particular of the large, economically operated house networks. Attempts have therefore been made again and again to unite operators of the two network levels through mergers - but this usually failed due to resistance from the Federal Cartel Office . Experts suspect that the complicated interests of market participants can lead to a blockade of the necessary innovations and therefore repeatedly call for agreement on standards and business models. The question here is whether the dispute over end customer access is detrimental to the end customer. This is to be answered in the negative in the case of the large NE4 operators, as they themselves offer the lucrative additional services that are attractive to end customers. Here, when a contract for cable internet and / or IP telephony is concluded, the NE4 will be revised free of charge by a service partner. The smaller NE4 operators (housing associations, property management companies, etc.), on the other hand, often shy away from the necessary investments and mostly do not have the necessary know-how to set up a return channel network and to equip and operate this with additional services such as the Internet. However, more and more smaller operators manage to set up independent, return-channel-capable networks or have them done by specialized service providers. Some of them implemented the network expansion long before the network expansion at Kabel Deutschland and Unitymedia. Small, independent cable networks have been created there from former NE4 systems, regionally limited (from the street to the district).

Since August 1, 2019, Vodafone has had a monopoly in the German cable television network with the takeover of Unitymedia and a 76.57% stake in Kabel Deutschland .

Network level 5

Network level 5 describes the area from the junction box to the customer device z. B. TV, radio, receiver or cable modem . In practice, self-cabling behind the junction box creates most of the technical problems for NE4 operators, as insufficient shielding and unprofessional implementation lead to radiation emissions that are sent back into the cable as ingress and disrupt the reception of other participants. In the worst case, radio traffic can even be disrupted.

Telephone network

Just like in the cable television network, there are network levels in the telephone network. In contrast to the cable television network, the branch cables that form network level 3 do not consist of coaxial cables in the telephone network, but predominantly of copper wire pairs , and increasingly also glass fiber cables .

See also

Individual evidence

  1. ^ History of cable television from Kabel Deutschland. (No longer available online.) Archived from the original on August 29, 2011 ; Retrieved March 3, 2011 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot /
  2. The LMK on network levels. Retrieved March 2, 2011 .
  3. Richard Sietmann: Cable future - Internet via TV cable on the rise - without any fiber optic expansion . c't , July 8, 2010, accessed November 6, 2019 .
  4. Matthias Kempf: Structural change and the dynamics of dependencies. Deutscher Universitäts-Verlag , 2017, accessed on November 6, 2019 .
  5. Unitymedia purchase., accessed on May 9, 2018 .
  6. ^ Liberty Global to Sell Operations in Germany, Hungary, Romania and the Czech Republic to Vodafone. Liberty Global, May 9, 2018, accessed May 9, 2018 .