What is MDU in FTTH?

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1. What is MDU in FTTH?
MDU is multi-dwelling unit. It is mainly used for the access of multiple residential users under the FTTB application, and generally has at least 4 user-side interfaces, usually 8-way, 16-way, 24-way FE, or FE+POTS (fixed telephone) interfaces.

2. The development of MDU in FTTH

In the FTTB mode, the OLT equipment is located in the central office, and the typical distance covered by the ODN network is 3 to 5km. MDU equipment is placed in office buildings and residential buildings, and terminal users are accessed through VDSL2. The distance is generally less than 300m, and the user access rate can exceed 50M.

MDU is an important network node device in the FTTB construction mode. With the evolution of broadband access networks, it has experienced the transition from the first generation of small DSLAMs to the second generation of dedicated MDUs adapted to FTTx construction development process. The first-generation MDU generally implements fiber upstream access applications by adding PON interfaces to traditional small DSLAMs or desktop box-type products. The traditional small-scale DSLAM mainly takes village-wide coverage as the application goal, and does not consider bandwidth expansion in the design. At the same time, as a small or desktop application, the device function is relatively simple, and the environmental adaptability is less considered. In actual FTTx applications, due to different network construction goals and equipment environment requirements, as FTTB is applied to urban high value-added customer access, and the construction scale expands rapidly, the first-generation MDU has been difficult to adapt to current needs. Network construction urgently needs second-generation MDUs with high bandwidth, high performance, and strong environmental adaptability, which are specially designed for FTTB application scenarios.


Considering the application scenarios and future development of FTTB+MDU, the second-generation MDU must meet two requirements in order to adapt to the network transformation of ” optical advances and copper retreats “. The shared access bandwidth is greater than 30M, and the device capacity is greater than 100 lines. The second is the requirement of high reliability, easy maintenance, and strong environmental adaptability.

From the perspective of network construction requirements, the construction goal of ” optical advances and copper retreats ” is to increase network bandwidth. In order to protect equipment investment from rapid depreciation, equipment must be able to meet the bandwidth application requirements for a long period of time in the future. In 5 to 8 years, with the promotion and popularization of high-definition TV services, to ensure that each household requires two channels of high-definition TV, online games, and other broadband services, the access bandwidth should not be less than 30M.

At present, most of the network evolution of “optical advances and copper retreats” is constructed through FTTB mode, and the PON port bandwidth is generally 1.25G or 2.5G. With the development of PON technology, 10G EPON, and 10G GPON provide the possibility of optical fiber bandwidth expansion, which also requires as an optical fiber end device, MDU equipment will have the ability to expand with larger bandwidth in the future. At the same time, MDU equipment is deployed in densely populated areas such as residential and commercial areas, and users are high-value-added customers who are sensitive to bandwidth requirements. And because the line distance is less than 300m, VDSL2 can technically provide a bandwidth of about 50M, so it is required that there should be no bandwidth bottleneck inside the MDU equipment, and each user should be able to exclusively enjoy more than 30M of bandwidth.

3. The deployment of MDU in FTTH

In terms of network structure, the number of remote nodes increases greatly due to the downward movement of MDU nodes. In order to avoid the burden of the central office and make the network easy to manage, the capacity of the MDU equipment should be relatively high and flexibly configured. In addition, the construction conditions of MDUs are generally located outdoors, and they need to be equipped with outdoor cabinets or network boxes. Due to conditions, it is difficult to obtain the locations of outdoor cabinets and network boxes, and the space is relatively small. Therefore, MDU equipment is required to have a high degree of integration to meet the coverage of more people (It is usually required to cover 2 to 3 multi-story residential buildings, or a high-rise residential building within a distance of 300m).

As a remote node, MDU sites are distributed far away and in large numbers, and maintenance is very difficult after a fault occurs. The reliability and easy maintenance of equipment is particularly important for reducing the OPEX of telecom operations. When statistics on the failure causes of traditional corridor switches, it can be found that fan damage, lightning strikes, and power failures account for more than 80% of the total number of failures. Improving the reliability of the fan system and the protection capability of the line and power supply can greatly reduce the equipment failure rate. On the other hand, MDUs are generally placed in outdoor cabinets or residential corridors, basements, or patios, and have a high demand for environmental adaptability. MDU equipment needs to be able to adapt not only to the high-temperature environmental conditions caused by direct sunlight, but also to the low-temperature outdoor environment in winter. Moreover, since the equipment is placed in the corridor and close to the user, in a quiet environment at night, the MDU itself cannot have fan noise, so as not to affect the nearby residents. In routine maintenance, the maintenance of user access line faults and optical fiber line maintenance workload is very large. In order to reduce unnecessary manpower waste, support line MELT testing, and intelligent line positioning is very important.


These requirements are rarely involved in the application of small DSLAM or desktop equipment, but with the transformation of telecom operation services and the deployment of a large number of MDUs, the limitations of the first generation of MDUs have been exposed, and their design flaws have gradually been recognized by telecom operators. Most of the first-generation MDUs are designed from the original ADSL access central office DSLAM equipment, and do not consider the bandwidth requirements of end users. Generally, a shared ATM bus is used, and the equipment density is within 100 lines. Limitations make it difficult to expand bandwidth. In terms of environmental adaptability, it generally only meets -5℃ to 45℃ temperature range. The design of fan reliability, line protection, noise control, etc. also does not meet the requirements.

The second-generation MDU for FTTB application scenarios makes up for the above deficiencies, and is characterized by high bandwidth (20Mbit/s to 300Mbit/s per line), high performance, high reliability, and strong environmental adaptability. The second-generation MDU equipment adopts a new platform specially adapted to FTTx construction. The bus is a star design, and the VDSL2 slot has an exclusive bandwidth of 800M, which has the ability to expand to a larger bandwidth in the future. Design ambient temperature adaptation range -40℃ ~ 65℃ normal work. In terms of reliability, the n+1 backup, line and power protection of the fan system are supported to more than 4KV. The fan adopts automatic speed regulation design and uses a silent fan to ensure that the temperature at night drops to 35℃. No fan noise can be heard when below. It supports line MELT test, optical fiber line intelligent diagnosis, and can accurately locate faults.

4. The Market Distribution of MDU in FTTH

In Omdia’s Fibre Index 2020, Singapore scored the highest in fiber-to-the-home (FTTH) penetration, fiber-to-the-base station (FTTS) penetration, FTTH population coverage, and download and upload speeds. It is followed by South Korea, UAE, China and Japan. The top five countries all benefit from smaller geographic sizes and/or relatively highly urbanized populations – with a higher proportion of the population living in multi-dwelling unit (MDUs).

5. Factors to Consider When Laying Out Fiber-to-the-Home (FTTH) Networks in Multi-Dwelling Units (MDUs)

More and more people are now living in multi-dwelling units (MDUs) such as dormitories and apartments, and with the growing demand for high-bandwidth applications such as HDTV, fiber-to-the-home (FTTH) has become an irreversible trend, so how to deploy fiber-to-the-home (FTTH) networks in multi-dwelling units (MDUs)? What do you need to consider?

Before starting the installation, we should design a reasonable fiber network architecture for the multi-dwelling unit (MDU), the following factors should be considered in the design, the various possible combinations of factors will not only determine the deployment method but also which products to use.

5.1 New/Old Condition of Multi-Dwelling Units (MDUs)

There are various construction modes of FTTH network, and the situation of optical cable laying and routing is also different. If the multi-dwelling unit (MDU) is new, its construction is more suitable for access to modern networks, and it is easier to design a fiber-to-the-home (FTTH) network. If the multi-dwelling unit (MDU) is old, its network infrastructure may be outdated, and some are not even suitable for access to optical fiber networks, so there will be many restrictions when laying fiber-to-the-home (FTTH) networks, even consuming a lot of manpower and material resources. For the renovation of old residential areas, in many cases, it is necessary to add optical cable lines in the existing multi-dwelling unit (MDU). Generally, the existing cable ducts are used to realize the additional optical cable laying, and the laying method generally adopts the traction method.

5.2 Size of Multi-Dwelling Unit (MDU) Buildings

The size of multi-dwelling unit (MDU) is another factor to consider, that is, different sizes of multi-dwelling units (MDUs) are suitable for different fiber-to-the-home (FTTH) structures. In general, there are three types of multi-dwelling units (MDUs).


Low-rise multi-dwelling units (MDU) have a maximum of 3 floors and a maximum of 12 households. The fiber access point is usually outside the building, and it is suitable for each household to use a separate fiber.

The construction of the first-level light splitting mode is adopted, and each unit is usually equipped with an optical fiber direct fusion box, and the optical fiber direct fusion box is set on the middle floor of the building to reduce the laying length of the butterfly optical cable. The first-level light splitting point is generally equipped with a 1:64 light splitter, which is installed in the optical distribution box of the community.

Usually, each unit is equipped with an optical fiber splitter box (installed with a chip optical splitter), and the optical fiber splitter box is set on the middle floor of the building to reduce the laying length of the butterfly fiber optic cable in the installation link. The first-level beam splitting point is configured with a 1:16 beam splitter, and the second-level beam splitter point is configured with a 1:4 beam splitter. In areas with strong broadband services, 1:8 splitting can also be used for both the primary and secondary splitting points.

The mid-rise multi-dwelling unit (MDU) has a maximum of 10 floors, and the number of households ranges from 12 to 128. The fiber access point is set inside the building, and multiple users can share a fiber interface.

The mid-level multi-dwelling unit (MDU) has a large number of floors, and the users are denser. From an economic point of view, whether it is the full coverage method of the newly built area or the thin coverage method of the renovated area, it is recommended to use the second-level light splitting method, usually in the middle floor of each unit. An optical fiber distribution box is set in the weak current well. The typical construction mode is to configure a 1: 8 ( 4 ) optical splitter for the first-level optical splitting point, and a 1: 8 ( 16 ) optical splitter for the second-level optical splitting point.

High-rise multi-dwelling units (MDU) usually have more than 10 floors and the number of households is more than 128. The network architecture of FTTx terminal services is usually vertically distributed, and network cabling is spread across multiple floors and areas of high-rise multi-dwelling units (MDUs) to ensure every household can enjoy an efficient and reliable fiber-to-the-home (FTTH) network.

High-rise residential buildings have many floors and dense users. Usually, multiple optical fiber distribution boxes are set in each unit weak current well. Each optical fiber distribution box covers 24-48 households, generally no more than 10 floors.

The typical construction mode is that the first-level light splitting point is configured with a 1:8 (4) optical splitter, the second-level optical splitting point is configured with a 1:8 (16) optical splitter, and the splitter port is appropriately added later according to the user’s development.

5.3 Types of Optical Network Terminals (ONTs)

FTTH network consists of three parts: optical line terminal (OLT), optical network terminal (ONT), and optical distribution network (ODN). In fiber-to-the-home (FTTH) networks, the type of optical network terminal (ONT) and its location plays an important role in the maintenance and operation of the network.

There are two types of optical network terminals (ONTs): single-dwelling unit optical network terminals (ONTs) and multi-dwelling unit optical network terminals (ONTs). Among them, single-dwelling unit optical network terminals (ONTs) can be used in both single-dwelling units and can be used in multi-dwelling units, and multi-dwelling units optical network terminals (ONTs) are only used in multi-dwelling units.

In general, the cost of installing a single-unit optical network terminal (ONT) will be higher because the associated equipment is exclusive to one household. The multi-dwelling unit optical network terminal (ONT) is a unit building where residents share related equipment, but if the number of end users is large, since the end users are connected through copper cables and optical network terminals (ONT), the number of copper cables also required a lot, and the cost will also increase. In addition, we should also consider network speed and security, and the broadband speed provided by the single-unit optical network terminal (ONT) will undoubtedly be higher and more secure.

6. Summary


Now, access to fiber-to-the-home (FTTH) networks in multi-dwelling units (MDUs) has been widely admired, which greatly meets people’s needs for high-bandwidth networks. When laying a fiber-to-the-premises (FTTP) network, it is necessary to use a variety of fiber-optic cables, fiber distribution hub (FDH), fiber-optic distribution terminals (FDT), and other related fiber-optic hardware equipment. If you have any needs, please contact us, and Bonelinks will provide you with one-stop FTTH solutions for MDUs.

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