FTTH solutions for MDUs
Indeed, old technologies are reaching the limits of their performance, so new solutions are needed and network infrastructures must adapt to meet these growing demands. In the outside plant network, this means that fibre optic cables are gradually replacing copper cabling deeper in the access network.
Multi Dwelling Units (MDUs) play a central role in these developments. The high density of end users in these buildings makes them potentially profitable; however strategies to connect an MDU to the network depend on many things. For example, tapping the MDU market requires detailed knowledge of local conditions, including regulatory issues. Diverse communication structures have developed over time in each EU country, and there are numerous regulations and prerequisites that must be observed.
Deploying in a particular neighbourhood or connecting to any particular building depends, too, also depends on whether an existing infrastructure is to be updated, or whether the building and its neighbourhood are newly built. To anticipate and respond to the multitude of connection scenarios, flexible and adaptable solutions are essential – solutions that can be easily adjusted to the requirements of a specific environment.
In Europe, major service providers most commonly deploy P2MP (Point-to-Multi-Point) fibre optic networks. When take rates increase, splitters are often added to connect customers, and so-called “plug-and-play” solutions based on fibre optic connectors are used to provision services.
Municipalities and smaller city carriers tend to favour P2P (Point-to-Point) networks, often with permanent splice structures. Due to the diverse requirements of different connection scenarios, there is no best option; rather, both technologies, splicing and connectorisation, must complement each other in a flexible, complete solution that fits the project in question.
MDUs are of vital interest for FTTH carriers
According to reports, more people live in MDUs than in any other type of home, with more than 35 percent worldwide being apartment homes. In Europe, this number is even higher (about 50 percent) and in larger European cities more than 70 percent of the people live in MDUs.
In dense residential areas, MDUs with three to eight stories constitute the majority of the buildings and there are often 24 living units per block, on average. Furthermore, commercial areas are often situated alongside or among blocks of flats, while detached and semi-detached houses are sometimes neighboured with small/mid-sized companies.
Broadband service providers can supply a large number of end customers within a small area. As the living density is high in MDU environments, the relative cost to deploy FTTH in MDUs is lower compared to individual residences, although the cost is strongly dependent on the building circumstances.
A density increase from 4000 people/km² to 8000 people/km² reduces the cost of civil engineering and cable installation cost by 30 percent (iDATE). However, to implement a fibre optic solution, a coherent and complete concept which can be adapted to various connection scenarios is required.
The access area
MDUs are linked from the exchange either directly using a dedicated fibre for each customer or using splitters in enclosures in the field or building. The structure of the fibre optic network generally follows that of the existing copper infrastructure. In the route to the MDU, the gas and water supply channels running beneath the pavement are often nearing full capacity.
Feeding in additional cables for the FTTH infrastructure may be difficult and often requires costly excavation work. If empty conduits or ducts are available, fibre optic cables can be blown into them over several hundred metres (using blown-fibre injection technique). Open-air cabling to the building is not usually considered, although this is commonplace in many countries.
Distributor design
The way in which the fibre optic cables are laid, terminated and stored has a direct influence on the performance, lifespan and economic efficiency of a network. Cable management is subsequently of great importance and determines the network’s flexibility to adapt to future requirements.
Depending on priorities, a network operator can decide to use a connectorised/factory pre-terminated approach, splicing or a combination of both. Connectors and optical splitter solutions guarantee faster provisioning and network upgrades (e.g. splitter PON to WDM PON). Splicing is used for example if a connection is difficult to reach or if a lack of space prevents the use of a cabinet with a cross-connect function.
The trend in Europe is to go for a hybrid solution, because most brownfield MDUs have a congested building infrastructure. This means that fibre optic cables are pre-terminated or connectorised at one end and spliced at the other: the least accessible or difficult end is pre-terminated and the other side is spliced in the field.
Different building architectures
MDUs represent a huge challenge for fibre optic cabling and necessitate an individual design to ensure that the FTTH network is able to scale the individual floors efficiently and reliably. With MDUs in particular, it may be advantageous for the operator to migrate from the FTTB concept to FTTH. In FTTB deployments, the fibre optic cables reach only as far as the building. In this case the operator must switch to the existing, mainly copper-based infrastructure while avoiding connection gaps.
FTTH requires fibre cable be run to each unit. The effort required to re-cable an MDU is technically laborious and demands that a number of legal issues be addressed. Subsequently, directly supplying each unit with fibre optics depends on cable laying options available as well as unit ownership structures.
These buildings also sometimes have vertical and horizontal cable ducts, which already contain coaxial cables for cable networks or other supply lines like UTP cabling. Fibre optic cables may be fed through the cable ducts; due to their physical properties, they can also be laid together with power supply cables.
If there are no suitable cable ducts available, network engineers are confronted with the challenge of feeding the cabling into the separate floors without exorbitant cost and without leaving any visible traces of the installation behind. In some older buildings, it may not be possible to lay fibre optic cables retroactively – this depends on the state of the respective building.
Fibre optic connection of MDUs
Project planning and logistics are two of the greatest challenges when connecting a building. Foresighted project planning helps to keep time and logistics expenditure as low as possible, thereby reducing overall costs. During the conceptualisation of an MDU connection, a number of questions need to be addressed. For example, what is the type, age and state of the building, how is the building used, what cable access is there and is the existing infrastructure a pure copper network.
The connection is usually carried out in two stages: first, the fibre optic cables that are fed into the building from outside are terminated in the basement and the vertical riser cable going up to the different floors is installed. Here, the transmission medium is then switched to the existing copper network.
The direct connection of an end customer via a fibre optic cable is usually carried out later, at which point there are further issues to consider. In contrast to the USA, in Europe, cables or piping are rarely fed freely through the building or in on-wall cable ducts.
Technicians must therefore find other ways to reach the end customers on each floor, for example through disused chimney stacks. In this case, it is particularly important that the applicable fire prevention regulations and architectural requirements are observed.
With indoor cabling, the type of optical fibre and the quality of the cable are important factors; fibre optic cables work differently to copper cables and react to mechanical strain accordingly – with increased signal attenuation values. New developments in the area such as robust cables that employ single mode fibre with a reduced bend radius would thus play a key role in this scenario.
Connector or splice?
Traditionally, a mix of the two connection methods is employed. Connectors are often used in P2P networks in the central office and at the customer’s premises. Connectors may also be found in the outside plant area of P2MP networks – for example in distributors with optical splitters – where they are used for a fast and flexible access for testing and monitoring the network and for switching, upgrading or turning-up services to subscribers.
Choosing the most suitable method also depends on whether an infrastructure already exists and how the subject of collocation – that is, network access for alternative providers – is dealt with. To guarantee the successful and economic implementation of different scenarios, flexible, easily adaptable solutions are required. Essential here is finding the optimal combination of pre-configured standard components, individual adaptation, splice connections and connectors during the planning and installation stages.
About the author:
Sam Leeman is Senior Manager of Application Engineering for EMEA, TE Connectivity – www.te.com – He can be reached at TEteam@johnsonking.co.uk
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