NBN: Can vectoring work on Turnbull's FTTN?

Turnbull made an important point about his FTTN deployment yesterday:

Your existing ADSL modem is still going to work. [However, to get higher speeds, you'll need to buy a VDSL2 modem.]

 This tells us a whole lot about what the Turnbull-FTTN can and cannot do:

• The Coalition NBN policy claims "no disruption" in cut-over. This is how it's to be done.
• "Nothing done in the house" is also a listed advantage of the Turnbull FTTN, confirming phone services remain over "baseband" copper shared with DSL.

• Your NBN connection won't directly use the "Layer 2 bitstream", but the older, more limited & costly and slower current technology, PPPoE.
• The speed of PPPoE is limited by the CPU speed of the DSL access device you use.
• Multicast from the FSAM/PoI isn't possible are each client individually tunnels back to the ISP and their PPPoE server. [That's big and chews power, for no good reason.]
• Services will be limited to one RSP, not the four initially available on FTTP Network Termination Devices.

• It implies that your fixed phone will still share the same phone line.
• Which means the line will still have to be balanced & loaded for voice, not DSL.
• Plus you'll still need performance affecting line-filters. [Now is a really good time to get yourself a high-quality central-splitter.]
• If the line back to the exchange is cut as is required for vectoring, you'll need an "ATA" (Analogue Telephone Adaptor) either in your home or in the node. This is part of what an NTD does.

• If you're one of the ~1M lines connected via the 8750 Telstra RIM's (aka mini-muxes), then there's a problem. They are nodes and have to be disconnected and removed. 
• That conversion won't be simple or transparent.
• Or free, going on Telstra's track record.

Copper lines can be optimised for either voice or data (DSL), not both.

For DSL to work at all, a high-pass/low-pass filter is needed at the customer premises to separate the high-frequency DSL signal from the voice. You get the choice of a central-splitter, that pulls the DSL signal off when it enters the house onto a separate cable and leaves the house cabling only with voice signals, or a line-filter on every device.

Why you need to do this is simple & unavoidable physics: to DSL, a normal phone looks like a short-circuit and kills the signal. If a filter is not connected or fails, then your DSL service stops, or is severely compromised.

Vectoring relies on treating a whole group as an entity and dealing with near-end/far-end interference & cross-talk, group delay and echos all together.

A major part of the Telstra FTTN plans in 2005 was removing all the special conditioning of copper lines for voice. DSL services work much better, wasting less power and with less line noise, over 'bare' lines. It's a trade off: have your phone work or have DSL work well.

Vectoring will work much better over 'bare' lines as well. You can't have someone with a faulty line-filter or plug-in a new device without a filter.

But as of yesterday, we know that the Turnbull FTTN won't be 'bare' lines with an in-house NTD. It will be a much poorer version of that, with much reduced speeds and missing the essential technical underpinning of the NBN: end-to-end "layer 2 bitstream service" allowing multiple RSP's per premise.