Page 5 - 20180911 Access Transformation white Paper Final

Even though we have three levers there are only two upgrade actions within a type of access network architecture that can be
performed: a technology upgrade and an architecture upgrade action. In the rest of the paper we will examine how these upgrade
actions are applied in each type of access network.

Technology Upgrade Action

As mentioned in the introduction, for all the types of access networks, there are multiple versions of the technology that were
standardized over time. Each version improving drastically the maximum throughput the technology can provide over the given
medium. To do so technology upgrades typically both enhance the amount of spectrum that can be used on the medium and introduce
higher order modulation techniques. To make it less abstract, let’s look at the technology evolution for all the access network
architecture types in detail.

DSL Technology
Evolution

The amount of innovation
enabling more and more data
over existing telephone wires
[4] has been astonishing as
shown in the figures.
Throughput went from 10-20
Mbps with ADSL2+ introduced
in 2003/2004 to 1Gbps with
G.fast introduced in 2016/2017.

The increase in performance is achieved by the increase in the spectrum width as shown in the above figures combined with more
efficient encoding introduced with every new technology upgrade. Along the way some other interesting signal manipulation
techniques such as vectoring helped increase the available bandwidth even more. One of the issues with twisted pair copper wires in a
bundle is crosstalk which reduces the effective throughput on a pair far below the theoretical maximum for that technology. Vectoring
processors consider all the signals travelling in a bundle and can through calculation effectively remove the crosstalk, bringing the
throughput per pair back-up close to the theoretical maximum.
The downside of the technology evolution as shown in the figures is that the maximum distance over the copper wire is drastically
reduced with every upgrade. This has forced operators to fundamentally change the deployment model. Telco operators used to
deploy DSL from large DSLAMs hosted in the central office and send data over long copper loops to all the subscribers. With the
introduction of VDSL2, suddenly not enough houses were within the maximum distance from the central office forcing the operators to
deploy smaller DSLAMS in cabinets in the outside plant. Typically, these VDSL2 cabinets are fed with fiber cable from the central office.
As a result, these deployment models are called Fiber-To-The-Node (FTTN). Going beyond VDSL2, smaller and smaller cabinets need
to be installed closer and closer to the subscriber reducing the length of the copper and increasing the length of the feeder fiber. This
evolution process is also known as a “Fiber Deep” strategy.

The new deployment models in a fiber deep strategy are sometimes named after the location where fiber is terminated. Examples are
Fiber-To-The-Curb (FTTC), Fiber-To-The-Home (FTTH), Fiber-To-The-Building (FTTB) etc.

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