For many service providers, the price tag of a complete fiber
network overbuild is too steep to justify. But, even if they can’t
afford an overhaul of their network, they also can’t risk falling
behind their competitors in the quest to deliver advanced Triple Play
services.

A true, all-fiber network build-out is actually a rare undertaking.
It is fair to say that even the most prominent fiber-to-the-home (FTTH)
deployments underway today do not rely on fiber going all the way into
each and every end-users’ premises.

Instead, most providers today are taking the hybrid approach. Many
incumbent service providers around the world, including those in Japan,
Korea, North America and Taiwan, are utilizing or planning to utilize
existing copper infrastructure in some portion of the last mile, or in
the multiple dwelling unit (MDU) risers, in order to eliminate
construction disruptions and hasten rollouts and return on investments
(ROI) for new, advanced broadband services.

These hybrid architectures rely heavily on VDSL2 technology. With
VDSL2 running over the copper portions of the access network, service
providers are capable of delivering symmetrical speeds of up to 100
Mbps and support Internet protocol television (IPTV), networked gaming,
peer-to-peer, and a variety of other broadband-intensive applications.

FTTH Includes FTTB
A full-fledged FTTH deployment is costly and time-consuming because all
new infrastructure must be deployed. Carriers such as Verizon and NTT
have previously reported (in 2006) that their per home installation
costs range from $1,000 to $1,750, depending on the carrier and region.

Other carriers, such as KT and CHT, have also announced investments
in FTTH. While their per home installation costs are not easily
available, they are generally expected to be similar. Such per home
infrastructure deployment costs require the service provider to be
patient to earn a return on their investment.

Figure 1. Schematic of VDSL2 in FTTB. 

A subset of FTTH is fiber-to-the-building (FTTB). FTTB is used
primarily in densely populated settings in which MDUs such as apartment
buildings, condominiums and hotels are prevalent. Fiber is terminated
in the building and VDSL2 runs over the existing copper infrastructure
in the building risers. In many cases, this architecture is one of the
only options in existing high-rises because riser space is limited and
typically filled to capacity with copper. (See Figure 1-in print
issue.) Many carriers around the world, including those in Asia, Europe
and North America are already deploying or planning to deploy the FTTB
architecture in their high-density urban regions.

By deploying VDSL2 on the copper in the risers in the FTTB
architecture, service providers are able to maximize copper
utilization. They can also offer higher value services on a higher
bandwidth platform, because the loop lengths are short and the
infrastructure is more protected, compared to the outside plant.

For example, with VDSL2, providers can use the full 30 MHz spectrum
and provide up to 100 Mbps symmetrical bandwidth. This can give the
carrier bragging rights for the highest bandwidth Last Mile access
services and, more importantly, enables High-Definition (HD) IPTV and
other advanced broadband services.

There are other deep-fiber architectures that, when combined with
VDSL2 technology over Last Mile copper infrastructure, can offer many
of the same performance advantages as a FTTH deployment. These
fiber-based architectures include fiber-to-the-node (FTTN),
fiber-to-the-remote (FTTR), and fiber-to-the-curb (FTTC).

With FTTN/FTTR/FTTC, optical fiber is terminated in a remote
terminal – often a cabinet that serves an entire neighborhood. At the
remote terminal, the signal is then converted from optical to
electrical so it can ride over existing copper infrastructure using
VDSL2.

The vast majority of service providers worldwide have em-ployed this
type of FTTN/FTTR architecture. Those carriers include Belgacom,
Deutsche Telekom and Swisscom in Europe; and AT&T Corp. in North
America.

Using a FTTN/FTTR/FTTC architecture enables service providers to
deploy high-capacity fiber to a central location in a neighborhood,
where that capacity can be shared among all homes in a neighborhood.
There are a number of benefits to this architecture:

Benefit 1. Less customer disruption. Because existing copper
infrastructure to the home is being used, service providers do not have
to dig up and install new wires to a home.

Benefit 2. Faster time-to-market and return on investment (ROI). Using existing copper speeds deployment and results in faster ROI.

Benefit 3. Cost containment. Compared to a complete fiber overbuild, an FTTN/FTTR/FTTC deployment is expected to be significantly less expensive.

The primary disadvantage to FTTN/FTTR/FTTC is that this architecture
is viewed by some as an intermediate-term solution. As bandwidth
demands increase and new broadband applications are introduced, service
providers will need to push fiber closer to the homes to ensure quality
of service and user experience.

FTTC is similar to FTTN/FTTR, but extends fiber closer to each end
user. The fiber terminates at the curb of the home, and uses copper
infrastructure to reach the house. By not extending fiber all the way
to the home, service providers eliminate many consumer inconveniences,
such as digging up yards to bury fiber or installing new equipment and
running new lines into the home. However, this method is more costly
than FTTN/FTTR since more fiber and construction is required.

Performance and Standards
Service providers undertaking FTTH deployments are relying on one of
two common standards: Ethernet passive optical networking (EPON), and
gigabit PON (GPON).

EPON is popular in the Japanese market and is making inroads in
other Asian countries, including China and Korea. EPON is based on
Ethernet technology and the IEEE standard P802.3ah. EPON can deliver
data streams of up to 1 Gbps, and operates at a distance of up to 20 km
between the optical line terminal (OLT) and optical network terminal
(ONT). EPON OLTs support up to 32 individual users on each PON port.

GPON is based on ITU-T standards G.984.1, G.984.2, G.984.3, G.983.4
and G.983.5. It is being launched worldwide and is expected to be the
FTTH technology of choice in Europe and North America. GPON is based on
generic frame protocol (GFP), which offers an open interface for more
efficient transport of a variety of protocols. GPON delivers
symmetrical and asymmetrical combinations of speeds up to 2.5 Gbps and
operates at distances of up to 37 km between OLT and ONT. GPON can
support up to 64 individual users per PON port. Newly approved
standards G.983.4 and G.983.5 offer, respectively, a specified dynamic
bandwidth assignment (DBA) mechanism and protection options that
enhance survivability.

VDSL2 also is being incorporated into fiber architectures to deliver
high-speed access over existing copper loops in the last mile. VDSL2 is
a physical layer technology for access networks that uses discrete
multi-tone technique (DMT) modulation to offer high bandwidth to the
consumer. It has 8 profiles defined for a variety of applications,
ranging from short loops to very long loops, and therefore, is a
universal technology for access deployment.

New VDSL2 products support a variety of new features, such as
integrated Quality of Service (QoS), enhanced impulse noise protection
(INP), seamless rate adaptation (SRA), Rapid Rate Adaptation (RRA™)
technology and channel bonding, all of which can potentially improve
the quality of enhanced services.

Another key benefit of VDSL2 is that it supports end-to-end IP
transmission, which is the technology of choice for all new access
deployments. As carriers push fiber closer to the consumer, VDSL2
enables them to deliver revenue-enhancing, value-added services quickly
and cost-effectively over existing copper infrastructure from the node,
remote, curb, or even in the risers of a multi-tenant building.

While FTTH offers service providers the best path for establishing a
network that is capable of meeting bandwidth demands long into the
future, the upfront costs and lengthy deployment process are higher.
The future of Last Mile access infrastructure is expected to include a
combination of FTTH, FTTB, and FTTR/FTTN/FTTC.