Is ADSL up to the task‾

Many carriers around the world are betting on ADSL to handle their IPTV deployments. But the complexity of the ADSL standard is creating uncertainty and slowing implementation

Carriers preparing for IPTV rollouts in Asia and the rest of the world are placing a large bet on ADSL and VDSL technologies to provide the bandwidth necessary for successful deployments. While DSL-based solutions often provide a more efficient and cost-effective alternative to full-scale fiber deployments, they too, present significant challenges for service providers.

Complexity, standards confusion and interoperability challenges are all combining to delay VDSL deployments in markets such as Asia and North America.

In a recent study, Vince Vittore, a senior analyst with Yankee Group, concluded that large-scale rollouts of VDSL.2 - a base technology for deploying triple-play services and IPTV - will be delayed until at least the middle of next year. Additionally, Vittore added, the lifespan of ADSL2+ (which is being used by some service providers as an interim step to VDSL) will likely be expanded because of continued VDSL snags.

'You've gotten delays in every flavor of DSL that has rolled out,' says Vittore. 'These are the types of delays you would get in any new technology.'

In his report, Vittore notes that the complexity of VDSL.2 is causing difficulties. The first VDSL.2 standard, ITU G.993, was approved in 2005 with the expectation that many telcos would deploy it by the end of last year. But that hasn't been the case. 'In an effort to push through the first of the two standards that make up VDSL.2 faster than normal, the ITU allowed multiple parties to contribute to the final standard,' notes Vittore. 'The result is a standard that has become highly complex and has several iterations.'

He isn't the only analyst with concerns. In a recent report about FTTP and VDSL, Analysys analyst Martin Scott warns that ADSL2+ lacks sufficient capability for IPTV when high-definition television is included in the equation. 'Real-life speeds of all DSL technologies can be as much as 40% lower at source than their theoretical maximum, and despite continuing improvements in digital processing, ADSL2 does not leave a lot of reliable bandwidth to play with over and above one HDTV stream,' he says. He adds that ADSL2+ can't cope adequately with HDTV bandwidth needs, so when it becomes the standard, VDSL.2 or fiber will need to be used.

Carrier confusion

All of this is causing confusion and some concern among carriers that have cast their lot with ADSL2+ and VDSL.2. Timeliness is a key issue for carriers in competitive markets such as North America. They are desperate to deploy IPTV as part of a triple-play solution to match aggressive cable competitors.  For example, in the US, AT&T opted to proceed with a VDSL-based IPTV deployment because it was much less expensive (one-third to one-quarter the cost) than the estimated $25 billion being spent by rival Verizon to lay fiber to the curb in its service area.

But AT&T has significantly slowed its original deployment schedule and lags behind Verizon. In March, the company quietly admitted its broadband network will reach only eight million of the 18 million homes it originally promised to pass this year.


The service is now available in only 13 markets in five states.

Vittore notes that AT&T is using compression technology to squeeze its IPTV signal to move it over ADSL2 lines until the VDSL.2 standard is finalized. Such a solution is suitable, but not preferred: customers wanting to use AT&T's system on separate HDTV systems in their homes, for example, probably would not be able to do so because of bandwidth constraints.

Another problem with VDSL.2,Vittore adds, is that it includes eight different profiles to satisfy disparate carrier needs. As a result 'vendors have had difficulty developing chipsets that meet such varying requirements in the early phase of the VDSL.2 lifecycle,' he notes.

Asian deployments

The Asia region is actually out ahead in VDSL deployment, at least for the moment. VDSL is popular in Asia because it is better suited for densely populated areas and multiple-dwelling implementations. Select Asian markets such as Japan and Korea have deployed the earlier VDSL.1 standard for several years to meet surging demand for ultra high-speed data above 25 Mbps. Yankee Group estimates there are nine million customers for VDSL.1 in those countries.
'Carriers in both of these markets have shown a willingness to deploy 'pre-standard' equipment, and are under intense competitive pressure to offer residential data services up to 100 Mbps,' Vittore notes in his report. 'Both markets also have a high percentage of residents living in multi-dwelling units where copper loop lengths are extremely short.'

In Hong Kong, PCCW currently serves 750,000 IPTV subscribers using ADSL. 'We predominantly use ADSL for our broadband provision, but this is changing to ADSL2+ as we ready for HDTV,' explains Paul Berriman, head of strategic market development. 'We do deploy VDSL in commercial buildings for commercial customers.'

Berriman adds that PCCW will probably move to VDSL for residential broadband in the future 'as demand for higher-speed uplinks and symmetrical services rises.' Although he concedes that VDSL is more complex and isn't yet fully standardized, he is confident ADSL2+ will be suitable, even with HD included, to meet short-term needs.

In fact, ADSL has many strong proponents, despite the problems and complexities. Danny Goderis, director of product marketing for Alcatel-Lucent's access division, calls ADSL 'the winning broadband access technology for high-speed Internet access. It's reliable, it's available, and it serves mass-market needs very well.'  AT&T, Korea Telecom, Swisscom, Belgacom, KPN and Deutsch Telecom are among the companies deploying VDSL today, he said.

'As with any new technology, VDSL needed some time for deployment and experience to optimize and exploit the full broadband copper capabilities,' Goderis says, adding the technology benefits from being relatively easy to deploy and manage.

'The initial challenges were in the operational deployments and in development of tools and functions to make VDSL stable for IPTV, because the quality requirements for IPTV are much higher for Internet access,' Goderis notes.

Vittore says Yankee Group expects that worldwide VDSL.2 deployments will be delayed as chip vendors work on resolving the issues. 'At the same time, we expect an increase in deployment of ADSL2+, which is more stable,' he says. 'Using ADSL2+ carriers can offer total bandwidth of up to 15 Mbps over loop lengths up to 6,000 feet.


That is sufficient to provide a single high-definition video channel and perhaps one or two standard-definition channels, assuming the latest compression technology is used.' Carriers that haven't yet committed to FTTP deployments likely will be forced to rely on ADSL2+ for longer than they expected. He urges telcos to plan for these longer-then-expected ADSL deployments, revisit their FTTP plans in markets where competitors launch consumer services above 25 Mbps, and push interoperability but not require it.