The business proposition is based on the upcoming, sustained VDSL2 capacity increase from 20 to 50 Mbps. This will enable service providers to expand their current triple play services into robust and future-proof offers.  The principal issues are line stability and power consumption.

An earlier article asked the question “Is IPTV (News - Alert) over copper a valid business proposition?” This was the conclusion:

The combination of FTTN (fiber to the node) and VDSL2 running at up to 50 Mbps represents a powerful, pragmatic solution that should enable operators to expand their current 20Mbps service offers and go on to build a robust market for triple play services. FTTH (fiber to the home) will be the end game, but the ability to generate near-term revenues is clearly a business-like way to finance that investment, particularly in the current economic climate.

Interrelated Issues

There are technology issues; life would be terribly dull without issues. A network based on FTTN will obviously consume more power than one based on FTTH. One reason is the fact that additional equipment is installed between the operator’s central office and the end-users. And the network will consume the maximum amount in peak viewing times, far less in the night.

There are power saving technologies that switch to a lower bit rate and power when user traffic is low, but they are not widely deployed for stability reasons. Power fluctuations on so-called “green” DSL lines generate cross talk (resulting in poor quality reception) and this can even result in modem resyncs (resulting in the end-users having no reception at all).

So there’s a dilemma: continuing to run the network at full power is not acceptable to service providers, while consumers are not going to accept poor quality transmission. This is an issue that has to be addressed in order to deliver the highest possible bitrates, at the lowest possible power.

Smart DSL Stabilizes Lines

The term “Smart DSL” comes from Alcatel-Lucent (News - Alert), as does the technology. Adding Smart DSL to the two power saving technologies — L2 Power Mode and MaxSNRM — circumnavigates the issue of line stability. It’s based on the addition of “virtual noise”, i.e. virtual crosstalk, which at first sight would seem to be something that compounds the problem. 

Figure 1 visualizes the way that crosstalk increases and DSL lines go unstable when power surges occur. They will typically take place just before a popular early evening TV show. When usage changes rapidly from low to full power on one line then crosstalk on a neighborhood line will increase and it may cause the modem to resync.
Figure 1. Power management leads to crosstalk fluctuations, which can make lines unstable. (Source: Alcatel-Lucent)

There will always be a certain amount of noise on copper access lines. In order to prevent received noise interfering with the signal the service provider will set a “noise margin”, as illustrated in figure 2. However, this will reduce the amount of bandwidth that can be employed by the signal.

Figure 2. These are plots of bandwidth (vertical axis) against frequency (Source: Alcatel-Lucent).

Setting a relatively low noise margin doesn’t have a significant impact on service quality in a VDSL environment, i.e. there is enough bandwidth. The problem comes from the fact that the noise margin would have to be high enough to mask the introduction of more noise as a result of the crosstalk. And on regular “green” lines this figure is a guesstimate so the margin has to be set on the high side and then the loss of bandwidth does become significant.

Now it gets Interesting

As mentioned earlier, Alcatel-Lucent circumnavigates the problem by introducing “virtual noise” onto the line. The magnitude and frequency range of the virtual noise signal are determined in advance, i.e. before service deployment starts.

Alcatel-Lucent has developed a Network Analyzer that measures the noise conditions on lines and the results are used to determine the precise amount of virtual noise to be introduced on a per line basis.
 

This means that Smart DSL technology ensures that the optimum amount of bandwidth is available. The loss is kept to a minimum because the “real noise” margin can be very slow and, as illustrated, it only takes place over a limited frequency range.

The line is stable at all times and no modem resyncs take place. And — this is where we came in — the power saving technology can be safely employed. This results in saving of around 25 percent. In addition, the new-generation line cards, DSL as well as VDSL, are based on energy-efficient designs that take around 20 percent less power than the previous generation.

Distributed DSLAMs

Deployment architectures can also be used to provide IPTV services over copper in a more eco-efficient way.

In a regular, centralized deployment one DSLAM will house the line cards, each of which will connect to the local loop. Alcatel-Lucent’s product, known as an ISAM, has 18 line cards, each of which has 48 ports, which means that it can serve up to 864 locations. 

Alternatively, the company allows service providers to employ a distributed architecture. In effect, the node is split up into smaller ISAMs and this allows the line cards to be deployed nearer to the various locations. This architecture uses a central network controller instead of one per node.

Alcatel-Lucent states that power consumption is reduced up to 20 percent compared to a traditional deployment where there is one dedicated controller per node. In addition, configuration and maintenance costs are reduced up to 40 percent and CAPEX for the aggregation link can result in savings of up to 60 percent.

Conclusions

FTTH will be the end game, but the ability to generate near-term revenues using services based on FTTN and “issue free” VDSL2 is clearly a business-like way to finance that investment, particularly in the current economic climate. For example:

In the UK BT (News - Alert) recently announced that their rollout will be FTTN, with the final connection to the home being a VDSL2 service over copper. And in the US many service providers see DSL as a service foundation. Qwest (News - Alert) is expanding its FTTN network with VDSL2 selected markets and the CEO Ed Mueller thinks that the network will be an anchor that could deliver high definition video services.