Fiber at any price

Staff Writer
10 Mar 2006
00:00

 

'You can run fiber to the cabinet in most cases.'

The downside, he notes, is that you're still using DSL to connect the user, although newer, faster versions of DSL like ADSL2+ and VDSL2 can mitigate this. However, he adds, the amount of active equipment in the cabinet becomes an issue. 'When you put more equipment in the cabinet, you add on to existing issues like space, power supply, temperature range and maintenance.'

FTTH's pros include virtually unlimited bandwidth to users, no active equipment between the user and the cabinet and high security. The chief drawback is the exorbitant cost of rolling fiber to individual homes, the cost of maintaining high fiber counts in the second mile and supplying enough backhaul bandwidth to support a neighborhood where everyone has a 100-Mbps broadband connection.

Get the point (or multipoint)

Another way of evaluating this is considering the benefits of point-to-point (i.e. FTTH) vs point-to-multipoint (i.e. FTTN/C) architectures.

'Point-to-point makes sense with short loop lengths when the network resembles a hub and spoke configuration - the central office representing the hub with spokes of fiber feeding each subscriber,' says Nicolas Van Den Abeele, vice president of access network activities for Asia Pacific at Alcatel. 'It becomes less economical as loop lengths and the number of homes passed/collected along the fiber route increase.'

Point-to-multipoint, by contrast, involves a single fiber leaving the central office that is split into multiple fibers in an outside plant, with the subtending fibers connected to individual subscribers from the point of the split (which can be many kilometers away).

'This makes sense with average and long loop lengths and enables the cost of the central office termination to be shared among multiple subscribers,' says Van Den Abeele. 'It also enables subscribers to be connected along the path of the fiber route, given the linear nature of most routes.'

Which architecture is the most cost-effective is largely a matter of geographical distribution of subscribers, says In-Stat analyst Victor Liu.

'For example, in Australia, the cost of FTTx rollouts is very high because you have to cover a comparatively small population spread out across a wide geography. It's a different story in a market like Japan, which is more densely populated and you're rolling out to multiple-dwelling units.'

Choose your PON

Another decision operators have to make is what passive optical network (PON) technology to use. The two primary choices are the ITU-T's Gigabit PON (G-PON, which supports Ethernet, ATM and/or TDM flows to and from the optical network terminal [ONT] at the customer premises), and the IEEE's Ethernet PON (E-PON).

Neidlinger of Siemens says that based on the number of supported ONTs (which depends on the data rate budgeted for each subscriber), E-PON is suitable for smaller deployments with data speeds of up to 100 Mbps per subscriber, while G-PON is better for larger deployments where data speeds per sub could be as high as 1 Gbps.

However, Van Den Abeele warns that E-PON has its shortcomings, such as no standards-based operational support channel for monitoring, diagnosing and configuring ONTs.

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