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13 November 2014

Adtran says it’s solved G.Fast/VDSL2 coexistence problem

The reception of telcos to G.Fast has been fantastic lately, according to Kurt Raaflaub of telecom equipment maker Adtran. He said that as recently as a year ago the telcos reception to G.Fast was a toss-up, but that Adtran is now lining up trials at a number of unnamed telcos.

While the technical standard is expected to be completed by the end of December 2014, there are still several sections that work groups will continue ironing out. The Vectoring element for G.Fast is mandatory and as such is pretty much done. Best management practices for FTTdp customer reverse powering and FTTdp network are two architectural items that will continue being worked on after the G.Fast standard is signed off on in December.

As an equipment maker, Adtran is very involved with telcos as to the best practices for installing G.Fast.

Broadcom, he said, is providing pre-ratified G.Fast chips for in house testing. He said most of the tests are in labs, not in field trials. He also mentioned Ikanos, Lantiq and the start-up Sckipio as suppliers of G.Fast chips.

In Europe, where Adtran is quite active, G.Fast and its fiber-to-the-distribution point (FTTdp) architecture is especially welcome because of the difficulty of deploying all-fiber networks especially in older cities with large concentrations of MDUs, older streets and buildings and cobblestone roads.

Most well-known emerging residential broadband applications require less than 100 Mbps, such as 30-50 Mbps per 4K streaming video. The 100 Mbps speed is in part justified by many countries’ regulatory bodies setting 100 Mbps broadband goals.

Most of the G.Fast chip and equipment makers have talked to us about the difficulty of supporting both Vectored VDSL2 and G.Fast in the same binders of copper wires. Adtran said there is currently no vectoring solution in cases where VDSL2 and G.Fast are both present [co-located] even though the G.Fast modems/gateways that’ll be installed in homes can support either VDSL2 or G.Fast.

Raaflaub said G.Fast is a sub-gigabit technology unless the performance stealing interference between VDSL2 and G.Fast is mitigated. Minimizing the interference impact of existing VDSL2 services on new G.Fast services can be accomplished either through complex cross-technology vectoring between VDSL2 and G.Fast or by deploying G.Fast services over very short copper loops, typically less than 100 meters, where the VDSL2 impact is only 10-20%.

This reality has spawned a new deployment architecture called FTTdp as copper distribution points by design have been installed very close to the end-user, sometimes as close as 25 meters. This is where G.Fast solutions could be deployed to maximize performance even in the presence of previously deployed 100 Mbps VDSL2 services.

Raaflaub said that rather than postponing all-fiber networks (FTTH), G.Fast can actually accelerate their deployment by providing a catalyst for the development of gigabit applications, which would in turn drive demand for all-fiber and hybrid fiber/copper (G.Fast) gigabit networks. These as yet unknown killer apps would push telcos to build faster broadband networks.

Back in August we talked about a white paper from Adtran called “Frequency Division Vectoring” which claims to explain the cause of the problems where vectored VDSL2 and G.Fast co-exist.

The key points made in this paper were:

While G.Fast is compatible with VDSL2, the data rate of G.Fast is reduced when it operates in a VDSL2-compatible mode of operation, dropping to as low as 10% of the full-spectrum rate at 400 meters, thus limiting G.Fast deployments to FTTdp and FTTB architectures.

Every VDSL2 subscriber in a cable binder shared with G.Fast must replace their existing modem for a new G.Fast modem to allow the subscriber base to be served with the higher data rates available from full-spectrum G.Fast operation.

By allowing both vectored VDSL2 and G.Fast simultaneously on a single subscriber line, service providers can offer performance equal to that of full-spectrum G.Fast on day one, without the burden of attempting to transition the entire base of VDSL2 subscribers to G.Fast technology.

Adtran’s patent-pending combination of VDSL2 and G.Fast on a single subscriber line is called Frequency Division Vectoring (FDV).

FDV provides a significant improvement in the rate/reach of the intermediate rate services — up to 2x the data rate for a given deployment reach, or 33% longer reach for a given service rate — compared to either a G.Fast OR vectored VDSL2 approach. A further benefit of the FDV approach is that it expands the deployment opportunities for G.Fast technology. With FDV, G.Fast deployments can be extended to cabinet sites. If Adtran has indeed solved the G.Fast/Vectored VDSL2 conflict, telcos will find it’s possible to deploy gigabit G.Fast in areas where Vectored VDSL2 is already installed.