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Adtran plans to use bonded VDSL2 to backhaul G.fast

Adtran seems to have come up with a pretty neat solution to the problem of getting fiber close enough to homes to then use G.fast broadband connections and it claims that it can savagely cut the costs of telcos installing fiber any closer than 650 meters away. The idea is to use bonded vectored VDSL2 lines as backhaul, not fiber for the last almost half mile.

It is pretty well understood that G.fast, even the latest 212 MHz version, attenuates rapidly as the loop length goes over 100 meters. So the usual practice is to take fiber that close to the home. The new approach came out under a product Adtran calls its Gigabit-to-the-Basement (GTTB) solution, part of its strategy to get a piece of the MDU broadband market.

Instead of dragging fiber another 100 meters closer to each cluster of homes, since copper lines must already go from the existing fiber connections to the homes, Adtran proposes using all the lines on vectored VDSL2 35b, which can each carry between 230 Mbps to 360 Mbps over distance, and bond them, and then re-modulate the signal using G.fast – so presumably cutting the lines to terminate them in VDSL2 35b and then re-attaching them to a G.fast distribution point. The G.fast is reverse powered from the home, but we presume the VDSL lines are powered from within the network.

We’re not sure at this point if other equipment vendors have offered the same type of solution, but Adtran is famous for offering miniature, sealed  broadband devices which can sit on powerline poles or under a manhole covers and still perform. But by this device’s name, we presume it mostly sits in the existing cross connect box and the other end in the basement of an MDU and we imagine it was developed for an attack on MDUs, which we know is the next frontier for broadband rivalry – beginning now (see separate story on AT&T).

Adtran said that typical Fiber to the Distribution Point (FTTdp) solutions extend fiber services by between 50 meters and 100 meters, but with its new GTTB) gigabit services can be extended out 650 meters from where the fiber ends which cuts construction and trenching out of requirements and gets time to market down to days or weeks rather than months or years. It could be that this approach was developed for AT&T, although we have never heard of Adtran being discussed in connection with that installation, but this would mean using AT&T existing lines in VDSL2 35b to backhaul G.fast over a coaxial cable within the MDU. And given that AT&T has just announced such a move this week (see separate story) it will have wanted to keep fiber build out for fiber services which were launched in parallel.

This new solution combines Adtran’s SDX 2200 series of 212MHz Gfast DPUs with its bonded Super-Vectoring (VDSL2 35b) which can support as many as 48 lines. We’re not sure if this creates a new vectoring issue, one for the VDSL 35b and another for G.fast, meaning that two instances of crosstalk cancellation have to be built in, but as we get closer to customers and deliver lines bundles to a low number of apartments like 16 or 24, the amount of crosstalk processing in the bundle is reduced and Adtran would usually build crosstalk cancellation into each device, so while it may affect the cost equation slightly, it might not change it that much.

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