Got copper access? You could already be ready for IPTV

 

IPTV and other emerging next generation video services such as VoD and Network-based Personal Video Recorders (N-PVR) are generating a lot of excitement (writes Ido Shargil
, Head of System Engineering at ECI Telecom & Chairman of iSMART Consortium). But that excitement is not shared equally by all. Bandwidth-hungry next generation video applications require the high-speed broadband access that currently only Fibre-to-the-Home (FTTH) can deliver. So, existing broadband subscribers who want to enjoy these services, but are not in the planned coverage area of their provider’s fibre access network, will be left out in the cold.

Unfortunately, there are some residential areas where FTTH deployment is not currently considered cost-effective. Some of these areas are in established urban areas where street cabinets are more than 200m from residences where copper access infrastructure would need to be replaced by fibre, requiring costly digging, construction, licensing and regulatory approvals. Without alternatives to FTTH, network operators are simply not offering some customers upgrades to high-speed broadband services.

As demand for next generation services increases, these geographical holes in the FTTH roll-out can lead to loss of revenue from potentially lucrative new services and erosion of the subscriber base as residential customers seek those services elsewhere.

For now, fibre access is the only widespread option available to telecom operators who want to offer high-speed residential broadband. However, there are alternatives to fibre being developed for commercial use within the next year or so. Most of the world’s existing wire-line access infrastructure is still copper-based. By exploiting that copper infrastructure, network operators might soon turn to these developing technologies to provide residential customers with the bandwidth they need for services like IPTV.

While high-speed VDSL2 technology can theoretically reach transfer rates exceeding 100Mb/s, VDSL2 has not been broadly implemented in the access network because of the limitations of copper as a medium. Copper suffers from electromagnetic interference both from ambient environmental factors and from the signals transmitted over the other wires bundled in a shared cable. This interference dramatically reduces the signal quality and the practical distance that a VDSL2 signal can travel.

There are currently two technologies that can overcome the interference obstacle, each in their own way, and each with unique advantages and drawbacks.

DSL Bonding

Originally developed in the 1970s as a way to multiply LAN speeds in an access or backhaul network, DSL Bonding technology can combine multiple copper pairs to provide a faster broadband connection. Alcatel-Lucent, Ericsson, ECI Telecom and other major telecom vendors are working on bonding solutions for high-speed broadband. Although it has been implemented in a variety of applications, bonding is still not a mature solution for delivering high-speed broadband on a large scale.

Development is progressing. But there are a number of factors that could likely hold back broad adoption of DSL bonding technology for residential high-speed broadband services.

• The high cost of customer premises equipment (CPE) to support DSL bonding can be attributed to the general lack of interest on the part of CPE vendors who have yet to see a commercial solution.
• Also, the potentially high cost of implementation would likely offer little or no cost savings over fiber access for residential customers.

With these cost factors in mind, the most likely applications for DSL bonding technology are for backhaul and for business customers who are not in any provider’s planned FTTH coverage area.

Vectoring

The root cause of the shortcomings of VDSL2 over copper for high-speed broadband is in the noise that is generated by the transmission signals themselves. Today, Dynamic Spectrum Management (DSM) technology, also known as vectoring, is applied to data transmission lines to address line noise. In fact, vectoring can also be combined with bonding applications to optimize bonding’s bandwidth multiplying effect. Level 1 and 2 DSM technology have been deployed to an extent and have been successful in improving network performance by around 20% – not really enough, though, to make copper a usable medium for high-speed broadband.

Level 3 DSM (DSM L3), on the other hand, is a solution that employs both software and hardware-based signal processing to practically eliminate the most significant type of interference in copper cables – Far End Cross Talk (FEXT).  This crosstalk among the many copper wires bundled in a standard cable is the leading cause of signal interference which reduces transmission performance. This is generally what makes copper unsuitable for high bandwidth VDSL2 transmission beyond 200 meters, or so.

For each line in the bundle, the DSM L3 processor dynamically estimates the channel FEXT and cancels nearly all of it using precoding. In other words, when the DSM L3 technology senses noise on the line, it creates ‘negative noise’ so that, in the end, the data stream reaches its destination reliably and at greater distances.

Street cabinets that currently house copper access points are normally too far from residences to be able to provide VDSL2 services. Without performance enhancement technology, using the vast existing copper access network to provide IPTV over VDSL2 would require operators to install many more costly street cabinets and build out the required infrastructure to reach the subscribers who are not in line for fiber access.

In recent testing by the iSMART Consortium, a leader in the development of DSM L3 technology, results indicate that when it is commercially available, DSM L3 technology could increase the coverage area of VDSL2 equipment by as much as ten times. In urban areas where street cabinets are within 1,000 meters from the premises – too far for standard VDSL2 – DSM L3, requiring one node instead of ten, could help network operators realize significant cost benefits with VDSL2 over copper access.

Since DSM L3 technology can be used with existing VDSL2 CPEs with just a software upgrade, it could become a cost-effective solution for service providers in terms of the ease and simplicity with which it can be applied to the existing infrastructure. 

One thing that all residential broadband subscribers have in common is an interface to the existing copper infrastructure. For those subscribers who do not fall within any planned FTTH coverage area, those good old copper wires could still end up doing the job for years to come. What’s more, these new technologies on those old wires could make it possible for high-speed broadband providers to continue to serve their customers with the most advanced services.

Source: IPTV-News