Triple-play to MDUs/MTUs ­requires the right equipment

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The market for triple-play services for multiple-dwelling unit/multitenant unit (MDU/MTU) customers presents a substantial opportunity for carriers. According to the National Multi-Housing Council, 14% of all U.S. households are in MDUs, making the potential market about 16 million homes. Triple-play service penetration in FTTP installations has been estimated to be around 30%. If MDU subscribers follow that pattern, the market penetration will be a little more than 5 million subscribers, a significant revenue base for service providers.

MDUs, however, pose special challenges for triple-play deployment:

• MDU residents want the same triple-play services as customers in single-family homes, yet the MDU infrastructure issues are quite different from those of single-family homes.

• To keep construction costs down, MDU drops have to be installed all at once, even though triple-play penetration would be expected to be about 30%. Single-family-unit drops, in contrast, can be installed when the customer orders service.

• Triple-play services require 25 to 50 Mbits/sec of bandwidth per subscriber, yet pre-existing MDUs/MTUs are wired with copper, not fiber.

• Some MDU residents may want only basic telephony and 1-Mbit/sec DSL, while others may want high-definition TV (HDTV) channels, high-bandwidth Ethernet, voice over IP (VoIP), or other advanced services.

• In some residences, occupants may need higher-level data services (for small businesses or telecommuting), as well as residential triple-play offerings.

• MDUs often have higher residential turnover, so the carrier must be able to reconfigure services for each unit on demand at an affordable price.

Carriers have found cost-effective ways to deliver triple-play services over FTTP to single-family units (SFUs). They install an optical line terminal (OLT) in the central office that serves multiple homes, and then they install a fiber drop and a single family optical network terminal (SF-ONT) at each home. The fiber drop and ONT at the customer premises provide up to 100 Mbits/sec of bandwidth, easily addressing the variation in subscriber demand for different combinations of services such as HDTV, VoIP, high-speed data, and so on.

When applied to the MDU/MTU, this technique would require running a fiber drop to each apartment and installing an individual SF-ONT at the end of each drop. While this approach would allow carriers to use the same type of ONTs they have used for single-family houses, it presents multiple installation and maintenance complications (see Figure 1).

ONT installation in the living units of MDUs/MTUs requires obtaining permission from the building owner and from each apartment dweller for the installation of fiber-a tedious process. Once permission is obtained, the physical drilling, drywall removal and replacement, and other construction activities are costly, time-consuming, and disruptive. Maintenance of this equipment involves the same access problems. Appointments for repair would have to be set up, and the sheer number of ONTs to maintain would grow with the size of the MDU in question, thus increasing maintenance costs over time.Th 214960

Figure 1. Using SF-ONTs to serve MDUs creates installation and maintenance problems.

In both new and existing MDUs/MTUs, the most efficient way to deploy individual SF-ONTs would be to “wire” the whole building with fiber at once, but much of this investment could be wasted. If history is any indication, only about a third of those households would be likely to subscribe to the advanced services. Thus, up to 70% of the fibers could be stranded without revenue-generating services-but the cost of running the fiber to each apartment applies to both the customers that take service and those who do not.

Of the residents who do subscribe, each resident may want a different mix of services, as previously mentioned. Carriers cannot predict which customers will subscribe to the services, and apartments change hands relatively frequently, adding to the financial risk of this approach. In fact, MDUs often have higher residential turnover, and services have to be reconfigured for each unit on demand.

Another issue with this approach is its effect on the demarcation point. In today’s MDUs, the demarcation point between the telecommunications network and the in-building wiring is set; the telco equipment is housed in a telco closet located on the side of the building or in the basement, and this clearly marks the end of the telco network and the carrier’s responsibility. The internal wiring in the building belongs to the building’s owner and is the owner’s responsibility. If the service provider installs ONTs in individual residences within an MDU, however, the demarcation point would be effectively extended into the building, creating confusion as to who owns and maintains what.

Another area of confusion is ONT powering. While different carriers are using different strategies, the most popular strategy in SFU FTTP installations is to have the homeowner (or renter) provide the AC power, while the carrier provides the AC/DC power conversion device and the backup batteries. The resident also maintains the batteries. In an MDU, however, power may or may not be individually metered, so this complicates the responsibility for powering the ONTs. Does the building owner provide the power? And more importantly, who maintains the batteries: the building owner, the residents, or the carrier?

Clearly, the SFU approach for MDU deployments is too expensive and complicated. In addition, it introduces confusion over ownership of equipment and responsibility when problems arise. It would be far simpler and less costly to maintain the existing demarcation point at the telco closet or enclosure.Th 214961

Figure 2. A centralized MDU ONT provides triple-play services simply and cost-effectively.

A multidwelling optical network unit (ONU) would preserve the demarcation point because it could reside in the existing telco closet at the building and deliver services to individual residences from there. This approach requires using existing copper wiring within each MDU to deliver high-bandwidth triple-play services. Fortunately, copper wiring runs in MDUs are typically short (less than 500 ft), and VDSL2 technology allows carriers to deliver up to 100 Mbits/sec of bandwidth over such short distances via the existing copper (see Figure 2).

A single fiber-fed terminal serving the building enables ownership of wiring and equipment to remain the same as before; carriers can have a single point of service when maintenance is required, and the initial deployment is far simpler and less expensive.

The ideal MDU approach for triple-play services would be an ONU capable of supporting multiple residents. The ONU would provide interfaces for the fiber connection to the central office along with multiple copper connections to the residents’ apartments. The ONU should be sized appropriately for installation in the telco closet or enclosure, thus retaining the demarcation point between the telecom network and the in-building wiring.

Centrally located ONUs are available in both fixed and modular configurations. Like an SF-ONT (which is a fixed-configuration unit that typically supports POTS lines and provides one data/IP video port and one RF analog video port), a fixed-configuration ONU for MDUs offers a set number of service connections of each type. The ONU might support 24 POTS lines and 12 data/video lines, for example, but many other line sizes could also be specified.

One drawback of a fixed-configuration ONU is that if a particular MDU uses fewer than the maximum number of lines, the unused ONU lines are stranded. By contrast, a modular unit gives the carrier the flexibility to plug in only the number of lines required at any site, greatly reducing stranding. Fixed-configuration ONU “bricks” tend to be less expensive on a per-line basis than modular units if all lines are used, but the cost of stranded lines and the need for flexibility for providing the right number and type of services makes modular ONUs more cost-effective.Th 214962

Figure 3. Many MDUs have businesses located on the first floors with residential units on the upper floors. Therefore, the ONU should be able to cost-effectively support many different service types.

The ONU must be able to use the MDU’s existing wiring to provide the drops to individual apartments or offices. Not only does this maintain the existing demarcation point, but it greatly reduces the service providers’ costs and complications of providing triple-play services.

The ability to provide triple-play services over copper up to 500 ft is a key requirement. An ONU that supports VDSL2 delivers the bandwidth of fiber (up to 100 Mbits/sec), but does not require fiber to be installed to each apartment or ONTs to be installed in each apartment.

MDUs come in a wide variety of sizes, from small buildings with four to eight units, to medium-sized buildings with 12 to 24 units, and all the way up to large MDUs with hundreds of units. The ideal ONU should be able to offer a few lines to a small building and many lines to a large building.

As demand within an MDU grows, service providers should be able to add more services to the ONU, or install additional ONUs as the situation warrants. In any case, the MDU approach must be flexible enough to serve a few or many subscribers. Here again, using a modular, chassis-based system with pluggable cards makes more sense than using a variety of fixed-configuration multiline/multiservice ONTs.

The ONU should be able to flexibly offer many different types of services in addition to POTS and DSL. Many MDUs (especially in urban settings) have businesses located on the first floors, with residential units on the upper floors. It is also not unusual for the building owner to have a business service, such as a DS1, in the building office. MDUs with businesses located in the building can require special services such as ISDN, coin, or DS1 (see Figure 3). With the current move toward Ethernet, native Ethernet service should also be available. PON supports these services, but fixed-configuration ONTs (either single- or multi-ONTs) can’t provide these special services cost-effectively, since the services are only needed occasionally. Plug-in cards, in contrast, provide that flexibility for the types of service and the number of services delivered.

The ONU should be designed to use the AC power source that is already located in the telco closet of a typical MDU, simplifying installation and minimizing expense. A centrally located MDU ONU eliminates the need to provide each apartment with its own power and batteries, which simultaneously improves reliability and reduces maintenance worries. The MDU ONU can either be locally powered or line powered. In the case of local power, either the carrier or the building owner provides the power and maintains the batteries. It is a business negotiation, not a technical issue.

It is also possible to line-power the ONU over the existing copper wires coming into the building. In this case, the carrier powers and maintains a power node in the network. The node then powers multiple ONUs in multiple buildings. There are both business and operational reasons to choose either of the power architectures. In either case, powering is simpler for the MDU ONUs than it would be if SF-ONTs were distributed to the apartments.

Finally, MDUs vary widely in their configurations and available space. If the demarcation point is in a telco closet, then the enclosure must have a lock to keep out unauthorized people, but it does not need any environmental protections. If the demarcation point is on the outside of the building (either wall- or ground-mounted), however, the enclosure must provide both security and some environmental protection.

The best solution would enable the service provider to use the same ONU either in an indoor deployment or an outdoor enclosure. Therefore, the electronics must be hardened and placed in different enclosures. These enclosures must provide a great deal of mechanical flexibility in terms of numbers of lines supported, in powering, and in the configuration of crossconnects.

The ideal MDU ONT fits the MDU. Where flexibility is important, it is a modular, chassis-based system with plug-in service and uplink packs. The system should be relatively small (24 to 48 lines) but stackable to service larger buildings. The system must support the entire triple play:

• Voice-both POTS and “specials.”

• Data-high-speed Internet service via VDSL2, DS1 service, and native Ethernet.

• Video-both IPTV and standard analog service.

And because each MDU deployment is different, the MDU should come in a variety of mechanical packages.

For the telco service provider, MDUs represent a rich source of new customers for high-revenue triple-play services. These customers will be the next wave for fiber deployments. But it isn’t possible to simply extend the successful single-family home fiber architecture to MDUs. The physical and business circumstances of these MDU customers require an approach unique to their location: a flexible ONU that can simplify delivery of these services and keep costs down for them and for the service provider.

Don McCullough is director of product marketing at Entrisphere (

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