Fabless G.fast silicon house Sckipio hopes to give the fibre-most-of-the-way, copper to the home market a kick along with silicon that gets close to symmetric performance, at whatever data rate the copper can support.
Talking to Vulture South after the launch, the company's marketing veep Michael Weissman explained the reference design for a single-port Distribution Point Unit (DPU), which Sckipio hopes will drive adopted by network owners trying to avoid that troublesome truck-roll to install fibre-to-the-home.
The DPU implements Dynamic Time Assignment (DTA), a technology the company proposed to the ITU and which received the standards-setter's assent in the standard as G.fast amendment 3.
Instead of configuring a network so that the downstream gets more time slices as upstream (unlike ADSL, which allocates capacity according to the frequencies used for downstream/upstream traffic, G.fast is a time division multiplexing scheme), DTA lets the distribution point respond to user traffic.
It can set allocations at 90 per cent down / 10 per cent up, all the way to 10 per cent down / 90 per cent up – and since the DTU responds to user demand, Weissman said it can feel pretty much like using a symmetrical service.
“If you're watching Netflix, nearly all of your traffic will be downstream. But if you're backing up your hard drive into the cloud, you can use 90 per cent of that capacity in the other direction.”
For networks using G.fast Weissman says it means there's going to be “a lot of capacity for a very long time, in the practical world”.
What's the catch?
The catch is, of course, that DTA was designed for a low-crosstalk environment (note - in its work with Calix, below, Sckipio is demonstrating DTA in a high-crosstalk configuration).
In a twisted-pair network, that means the best place for DTA is very close to the customer – once the pairs are split out of their bundles into individual cables.
The technology can also be applied to HFC networks, for example where that's been used as the in-building distribution in fibre-to-the-basement installations.
Since the technology is designed to sit alongside fibre-to-the-premises (FTTP) deployments, Weissman said Sckipio paid attention to making it as much like a “virtual fibre” environment as possible.
Hence, as well as its fibre-like speeds and latencies, the DPU is designed to play nice with passive GPON management systems.
“We are going to behave as if we are a passive node on the network – it's easy to provision this into the network, without much management integration.”
The GPON system will “see something that's much more like a CPE than an access device”, he said.
Power from the user
Like most fibre-to-the-distribution-point (FTTdP) solutions, the Sckipio DPU is user-powered, but here there are some characteristics the company hopes carriers will appreciate.
First, because it's a single-port device, it avoids arguments Weissman said have emerged with multiport user-powered systems – is each user contributing a “fair” amount of power? Are low-consumption households unfairly subsidising the power consumption caused by high-consumption users?
A second is that it's a low-power unit, pulling about 7 Watts; and unlike a DSL modem, the DPU powers down most of the time. Its fast-start means it can idle, and respond to a network request with a one-second power-up latency, he said.
He also noted that since the DPU is designed for “on the pole outside the house” deployment, it solves a problem G.fast suffers on longer cable runs: the dc power suffers badly from attenuation if power has to travel a few hundred metres.
It also gets rid of the need to provide chunky backup batteries: in the US, for example, “the FCC is requiring 8 hours for battery backup – with 16 to 24 ports, you need a big backup unit.”
On the 16-port Sckipio/Calix unit, Weissman said it was developed because at the moment, most G.fast deployments use vectored bundles.
It's designed optimising the system for the entire bundle, so as to get the dynamic assignment capabilities of G.fast in more conventional fibre-to-the-node (FTTN) deployments.
The system's management is designed to manage the time-slicing across larger port counts, “so you don't have different lines communicating at different ratios at the same time.” ®