Analysis by Herman Wagter, Chief Architect of CityNet Amsterdam:
The recently published architecture of the Australian FttH network shows an intelligent and interesting approach (courtesy Peter Ferris for explaining some details). The first observation is that even in a vast country like Australia people live closely huddled on a small part of the land.
About 67% of the population lives in the top 50 urban areas; if you include the major rural areas you can reach 85% of the addresses in 1.5% of the land. So it makes sense to provide 93% of the addresses with FttH and the remaining with radio (5%) and satellite (2%).
For the 90% which will get FttH they have chosen a surprising combination of options in their architecture. The next-best-thing to full point-to-point in my opinion, full with potential to support different kinds of technologies and future upgrades if and when needed.
Let me focus on the interesting choices: over-provisioning in a point-to-point topology in the deepest part of the last mile, under-provisioning in the concentrated parts of the outside plant.
The basic building block of their architecture is a group of up to 200 addresses. A fibre local loop is deployed with 3 (!) fibres per address. In an aerial deployment 12 local drop fibre connectors (pre-terminated drop line, no splice needed) are made available on the poles per 4 addresses and used when and how required. The same approach is used for underground cabling. This setup will allow for layer 1 unbundling future expansion, support of point-to-point Ethernet to businesses, multiple ISPs to same address, support for 3G/wifi mobile broadband and so on.
All fibres for these 200 addresses concentrate in a Fibre Distribution Hub (FDH), a cabinet in the street or cleverly combined with other uses like a seat in the park. In the FDH the connections are made to either a splitter (for PON) or a single fibre (point-to-point) in ducts leading toward higher layers of the network. It is even foreseen to change the splitters for filters if WDM becomes financially viable.
Up to 16 FD’s are concentrated into a Fibre Serving Area Module (FSAM, max 3,200 addresses). The capacity in the concentration cabling initially deployed is enough to support PON as a technology to each home, plus some extra for businesses and other uses. Some sort of redundancy is built in by an interesting “dual-loop” structure by geographical separate paths in the connection of FDHs to FSAM location. If needed the capacity to one or more FDHs can be increased by deploying more cables in that path.
The FSAM is a planning construct initially but it allows also for future expansion. The number of addresses is ideally suited to be served by a prefab active equipment cabinet (know as Controlled Environment Vaults, or APOPs in the Netherlands), if needed. These CEVs bear a lot of resemblance to the prefab APOPs Reggefiber deploys outside city centres. They can be truck-rolled to a given location, placed within a day.
At the start FSAMs are just a passive concentration point.
Again some redundancy is introduced by geographical different routes for the cabling to the Fibre Access Node (FAN, equivalent to an exchange/central office), maximum size 76,800 locations/addresses.
It makes a lot of sense for the geography with lots of suburbia. The key is having space in the street for these FDH cabinets. Just install a lot of point-to-point fibre in the part where a lot of labour is required (you don’t want to redo that ever) and allow for all kinds of upgrades, options for expansion, unbundling locations, active equipment deeper into the network, as you see fit in the future.
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