Compared to copper, FTTH offers limitless bandwidth potential at reduced operational cost. With advances in Next Generation Passive Optical Networks (NGPON) technology fibre can provide speeds in excess of 40 Gbps, as well as greater network flexibility to converge more services, facilitate co-investment in a common network infrastructure and deliver operational benefits.
However, due to extensive civil work requirements, and the need for technicians to enter the customer's home and drill holes in walls to complete the installation, FTTH deployments are often slow and costly. It can take years to deploy a national fibre network and the long wait can be frustrating for business and residential customers who have an immediate need for more speed.
Fortunately operators can now leverage advances in DSL-acceleration to cost effectively deliver more bandwidth and speed over their existing copper networks.
VDSL2 (Very High Bit Rate DSL 2) technology is breathing new life into copper and has been commercially deployed for years. It has the potential to deliver more than 100 Mbps to subscribers - enough bandwidth to support High Definition TV (HDTV), online gaming and meet national broadband targets. However, VDSL2 is prone to performance degradation caused by interference ("crosstalk") between copper lines packed together in a cable bundle. To overcome this, operators can deploy VDSL2 Vectoring, which uses a technique similar to noise cancellation headphones to cancel interference, allowing each line to operate at a predictably high bit rate at any given loop length (Figure 1). Combining vectoring with bonding (using multiple copper pairs to a subscriber) technology can double bit rates.
Figure 1: VDSL2 with vectoring
G.fast turbocharges copper
Service providers find that G.fast turbocharges copper and enables use of existing copper infrastructure to deliver "de facto" FTTH services. G.fast is an emerging DSL-acceleration technology that promises to deliver bit rates in excess of 1 Gbps (upstream and downstream) over very short distances of copper (<100 metres). Since G.fast is even more susceptible to crosstalk than VDSL2, it requires vectoring to live up to its potential in situations where multiple G.fast lines operate within the same copper cable.
G.fast extends the life of copper, allowing operators to deliver faster broadband to more people while gradually pushing fibre deeper into their access networks. Used strategically to complement FTTH, VDSL2 Vectoring and G.fast can fill gaps where fibre is not currently an option physically or financially.
In FTTH rollouts, a substantial part of the cost-per-subscriber is in the last few metres between the nearest roadside cabinet and the home. In logistically challenging locations, costs can be deferred by using VDSL2 with vectoring over existing copper phone lines. Once G.fast becomes commercially available, operators will be able to offer customers fibre-like Internet access over last-run copper. The first pilot deployment is expected in 2015.
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