Siting aggregation points

In a city like Amsterdam, space is a much sought after resource. We need space to erect buildings, public space for roads, bike lanes, car parking, and freely accessible parks with trees. So where could we find space to put a concentration point where all fibers meet and get patched to electronics, with cooling and power supplies and the like?

The first idea was to design small cabinets as APOPs for 1,000 customers or less, much like VDSL cabinets, and place them on the street in the public rights of way. Alas, the idea of erecting cabinets that emit heat and sound (fans for cooling) appeared to be a horrifying thought for the authorities. As one of them said, “450 new gathering and sleeping locations for vagrants and junkies? Never!”

In their experience, these kinds of cabinets tend to become a meeting place where waste is discarded and problems get concentrated. Combined with the realization that small APOPs make life very difficult for new entrants who want to take advantage of unbundling (small APOPs require much more redundant backhaul to reach the many boxes) the decision was easy: go for bigger APOPs, and stick them inside buildings.

Of course, this meant searching for available space in existing real estate, which had its own challenges, and negotiating contracts with each owner. It turns out you either can get very big APOPs in their own buildings, each concentrating 40,000 to 80,000 connections or more, or you can get “left-over space” in existing buildings, which was the preferred option.

There are more cellars, or corners of parking garages, or storage areas of 50m2 to 150m2 than one might expect in a major city. The requirement for an APOP not to have windows or recognizable doors fits nicely with space in real estate that is hard to find a tenant or owner for (and is therefore cheaper to buy).

A room of 100m2 can support an APOP for more than 10,000 connections, including patch cabinets, 19-inch racks for ISP/operator gear, cooling systems, and backup power supplies. The amount of electrical power needed is limited, so normal, business-grade grid connections can be used.

For a city like Amsterdam with 450,000 connections, finding 45-50 locations with an average 100m2 is doable. Therefore, the decision was made to go for APOPs in existing buildings with a size between 5,000 and 15,000 connections.

As we worked on Citynet, in other parts of the Netherlands, other FTTH projects were deployed. Everybody made the same trade-off on topology and decided to build a point-to-point network, so we compared our project with the remaining design choices made by others.

The difference in number of connections of APOPs was hard to explain until somebody started to compare the geographical coverage of an APOP: they all covered an area between 4km2 and 8km2. Apparently there is some natural size of a star network in an urban or semi-urban area; the density of housing determines the number of connections per APOP.

Surveying the area

Natural boundaries like waterways, highways, or railway tracks limit deployment options, but once a suitable APOP is located, the approximate geographical coverage supported by that APOP can be determined.

The next step is to survey the area: how many fibers are needed and what kind of pavement is used? Adding fiber later on is a nightmare, so you need to estimate current and future demand as well as possible.

Opening up and restoring the pavement can be very expensive, depending on the type of pavement and its age. Legislation requires you to completely redo pavement that is less than 5 years old, from curb to building. So it might be cheaper to bypass a beautiful crafted sidewalk in a shopping area which is a couple of meters wide, and instead take a small detour through old, narrow pavement. Tiled pavement is easier and cheaper to repair than concrete or tarmac.

A quick survey showed that most corporations tended to see a market for two or three FTTH-like connections for themselves.

The land register is a place to start, but it does not fill in the greasy details. Every street has to be surveyed for surprises. An official registered address does not say if it redirects to a houseboat on an Amsterdam canal, a garage box with no occupants, or a multi-story office building.

It does not tell you if the owner has decided to rearrange the apartments inside the building to optimize rental income (aka, “split the place up as much as possible”), or has decided to tear down the existing building and build something completely different in the coming years. All this has to be established by surveying, both on foot and by checking planning registries.

Big office buildings and special purpose buildings like hotels generate their own headaches. How many individual tenants will be there? Will they all need individual fibers and individual subscriptions to an operator or a service? What will they need 10 years from now?

Fortunately, these big buildings are less than 1 percent of the total number of connections, so they were considered to be less important. Most of the corporations and large institutions already have their own fiber connection delivered by a major business provider, with redundancies, specific SLAs, and you-know-what mandated by corporate IT. (No wonder these connections are much more expensive than a regular FTTH connection; they require a lot of customization and customer care.)

The physical network was optimized for the remaining 99 percent of connections to homes and small businesses. No redundancy in the access network, no special SLAs, no frills, no customization options for the corporate market, just get the price down by standardization. ISPs could later do whatever they wanted with these access lines to corporate customers as long as it was based upon the standard dark fiber spec, be it SDH, ATM, Ethernet or WDM.

A quick survey showed that most corporations tended to see a market for 2 or 3 FTTH-like connections for themselves: one for guest WiFi, one for the IT department to fool around with as a backup, and one for top management to have unabridged access to the Internet without the interference of their IT department. Add in a few spare fibers just to be sure, and you have your count.

The opposite are incubator buildings for startups where many small businesses resided, one per office. Every startup needs its own provider and its own voice and Internet solution, so every office gets its own fiber; it's almost Fiber-to-the-Desk.

As a design rule, a 10 percent spare capacity in fibers was added after the per-street tally was made. One of the potential uses for the spare capacity is backhaul for short-range wireless stations, as ubiquitous broadband will drive up demand for wireless as well as wired traffic.

Surveying buildings

Multi-dwelling units (apartments) and office buildings with multiple occupants create their own particular challenges. In dense cities like Amsterdam, approximately 90 percent of all housing is MDU, with anywhere from two up to 500 individual apartments per building. The technical challenge is to get the fibers that have been buried in the street inside the building, then distribute them up to each individual apartment.

Architects rarely consider utilities and cables as something other than a nuisance, and the building standards are based on copper wires for telephony and coax for cable TV to be put in place during construction. So nobody has given much thought to deploying new (fiber) cables inside existing MDUs... and it shows.

Most buildings have to be surveyed from the inside to get any idea of what has to be done to distribute the fiber cabling to each apartment. Sometimes the surveyors return with a pleasant surprise: when the architect has created a neat stack of utility cabinets above each other, accessible from the hallway on each level. Sometimes they return with a headache if the architect has preferred form over function and created many barriers to get to different floors.

How about the existing ducts and pipes which have been used for copper wires or coax cables—can’t they be re-used to get fiber to an apartment? Unfortunately not. There are legal and practical reasons for this (like the unacceptable gap in service delivery you create), but also technical reasons. Quite often the pipes are bent with sharp corners, or filled with dust or cement so you cannot get the original wire out of the duct, let alone put a new fiber cable in there. The lack of predictability is such a burden that it didn’t make sense to try to use these conduits.