Evaluating Options for The Last Mile
Over recent years, the industry has seen a significant rise in trials and deployment plans for new technologies to get more from the existing copper network. Whether carriers are looking to use copper technologies to extend the reach of their fiber investments, or use them in places where even a partial fiber network is not economically viable, they will be evaluating the options and likely considering the best fit based on:
• Maximum Bandwidth Needed
• Reach Required
• Economics
• Power Availability
• Housing Density
• Deployment Model Fit
In summary, if you need 100 Mb/s at more than 500 metres then DSL Rings is really the only option.
Figure 1 shows the maximum performance of each technology at a given distance.
Figure 1. Performance — bandwidth vs reach comparisons for DSL Rings, G.fast, and VDSL2 vectoring.
Reach Required
The reach required (i.e., the distance from the distribution point or cabinet) is a key determining factor in technology to select. The greater the reach, the fewer the options available.
Figure 2 illustrates the maximum reach capability of each technology at up to 100 Mb/s. It shows that if a performance of more than 100 Mb/s is required at a distance of more than 500 metres, then DSL Rings is the only viable solution.
Figure 2. Maximum reach over which 100 Mb/s (upstream and downstream combined) can be achieved.
Affordability and Economics
The economics vary greatly depending on the deployment scenario. It’s still not clear what the cost saving is to deploy fiber-to-the-DP and then G.fast vs. fiber-to-the-home. Ultimately however, the economic argument is valid only when the reach/rate requirement provides carriers with an option of technologies to choose from (i.e., in the less than 1,000-metre reach range).
Power Availability
Another challenge with G.fast that does not need to be considered when evaluating VDSL2 vectoring and DSL Rings solutions is the availability of power. There needs to be power at the distribution point, which is
not readily available, and back powering, using power provided by the customer, is a contentious issue.
Housing Density
The greater the housing density in a particular area, the more likely homes are to be 100 metres or less from the pedestal, the optimum distance for G.fast, and hence the easier it is to justify the cost of an extensive fiber deployment, provision of power to the pedestal as well as G.fast itself.
In less dense areas, where there may be 50 or fewer house per square mile, the distances from the pedestal to the home will likely exceed the viable distance for G.fast. Taking that into consideration, along with the fact that the average revenue per square mile is much lower, really makes utilising legacy equipment, the copper network, and DSLAMs a very attractive option.
Deployment Model Fit
With both G.fast and VDSL2 being vectored solutions, all houses serviced by the DP or Cabinet need to install the solution simultaneously to avoid the benefit of the vectoring being negated by cross talk. With DSL Rings it is possible to add houses to the ring "as and when" the customer wishes to subscribe to the service. The greater the number of houses on the ring the greater the performance to all houses due to the nature of the solution.
In summary, the right solution depends first on the bandwidth/reach requirement and then, if more than 1 technology meets those requirements, economic, powering, housing density, and deployment considerations.
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