For many service providers, the price tag of a complete fibre network overbuild is too steep to justify. An all-fibre network build out is actually a rare undertaking. Many incumbent service providers around the world - including those in Japan, Korea, North America and Taiwan - are utilizing 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. Venkat Sundaresan takes a look
FTTH is the ideal future-proof network architecture because optical fibre is connected directly from the service provider's network to the customers' premises. Fibre is capable of delivering extremely high bandwidth and outstanding error performance, while supporting transmission over long distances without requiring expensive repeaters.
However a full-fledged FTTH deployment is costly and time-consuming. For example, both Verizon and NTT are upgrading most of their infrastructure to all fibre - pushing fibre as close to the consumer as possible in order to ensure that they can deliver the most revenue-generating services well into the future.
Verizon and NTT are deploying fibre to single family homes, where it can be installed relatively easily. In its newsletter detailing financial results for the third quarter of 2006, Verizon reports that its fibre to the home (FTTH) initiative costs $1,745 per home - $845 to pass a premise with fibre and another $900 to connect fibre to the home. In Japan, NTT's costs are slightly lower. In fiscal year 2006, the company reported that incremental FTTH investment per user was approximately 130,000 yen, or about US$1,070. As a result of the high price tag of fibre deployment, service providers must be patient to earn a return on their investment.
Fibre to the building (FTTB) is used primarily in densely populated settings in which MDUs are prevalent. Fibre is terminated in the building and VDSL2 runs over the existing copper infrastructure in the building risers.
Verizon and NTT are using a hybrid approach - in which VDSL2 technology runs over copper deployed in the risers - to deliver broadband services to MDUs. VDSL2 is being used as the last mile technology because deploying fibre in restricted riser space is much more challenging.By deploying VDSL2 on the copper in the risers in the FTTB architecture, service providers are able to maximize copper utilization. With VDSL2, service providers can use the full 30 MHz spectrum and provide full 100 Mbps symmetrical bandwidth, which is capable of supporting IPTV and other advanced broadband services.
There are other deep-fibre architectures that - when combined with VDSL2 technology over last-mile copper infrastructure - can offer many of the same performance advantages as a FTTH deployment. However, the advantage of these architectures center around time-to-market and reduced capital outlay. These fibre-based architectures include fibre to the node (FTTN) fibre to the remote (FTTR) and fibre to the curb (FTTC).
With FTTN/FTTR/FTTC, optical fibre is terminated in a remote terminal - often a cabinet that serves an entire neighbourhood. 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 employed 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 fibre to a central location in a neighbourhood, where that capacity can be shared among all homes in a neighbourhood. Benefits include:
- Less customer disruption -service providers do not have to dig up and install new wires to a home.
- Faster time-to-market and return on investment (ROI) - A complete FTTH/FTTP overbuild takes a very long time, and on average, will not yield a return on investment for at least 15 years, according to Analysys, a UK-based research firm. A cabinet-based VDSL deployment can achieve ROI in about six years, Analysys noted.
- Cost containment - compared to a complete fibre overbuild, an FTTN/FTTR/FTTC deployment is significantly less expensive. AT&T, for instance, is using this type of architecture for its U-Verse service in the United States. The company is building out FTTN, and using VDSL2 to turbo-charge the existing copper loops entering the homes. AT&T has publicly estimated that the FTTN architecture costs only about $360 per user to deploy.
The primary disadvantage to FTTN/FTTR/FTTC is that this architecture is viewed by some as an intermediate-term solution. FTTC is similar to the FTTN/FTTR, but extends fibre closer to each end user.
While the deployment costs vary widely from FTTH to FTTB and FTTN/FTTR/FTTC, the performance of each can be virtually comparable under the right conditions.
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 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 being launched worldwide and is expected to be the FTTH technology of choice in Europe and North America. 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.
VDSL2 also is being incorporated into fibre 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 multitone technique (DMT) modulation to offer high bandwidth to the consumer. It has eight profiles defined for a variety of applications, ranging from short loops to very long loops, and therefore, is a universal technology for access deployment. As carriers push fibre 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. VDSL2 is in use today in Asia, by carriers in Japan, Korea and Taiwan, as well as in European countries, such as Belgium, Germany and Switzerland.
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 daunting. By employing a hybrid architecture, service providers can cost-effectively and quickly deliver advanced broadband services and generate revenue while establishing a migration path for future fibre installation.