NBN: MDU's not that hard with Cat-5? Or did I miss something?

I'm not a "Residential Fibre purist", especially when it comes to Multiple Dwelling Units (MDU's) as apartment blocks are called in NBN-ese. Today in the AFR, iiNet chief executive Michael Malone has called for "Fibre to the Basement" (FTTB?).

My guess is that Telcos want to wire VDSL inside buildings, following the Adam Internet example of VDSL2 to 1400 downtown apartments in Adelaide. Why not ethernet, as used in every business?


I think VDSL isn't a good solution, if it was then why aren't any medium or large businesses running their internal data networks?  Businesses can cost-justify very high costs for the benefits they receive: in this piece, I mention the Telstra rate card for a 10Mbps business service is $7,931/month for 'unlimited' usage (total 2.5TB) or 31 cents/GB for 100% link utilisation, vs $8/GB after 850GB/mth.

Apartments blocks designed and built after HFC Cable TV in 1996, especially up-market developments, will already be wired with Cat-5 or Cat-6, or have ducting, plenums and per-floor rack-space.

Body Corporates, the usual form of ownership, are quite used to dealing with Managed Service providers. These are the firms that would manage the installation and operation of the ethernet network.

Essential to the design would be full administration and control of all network equipment down to and including the per-premise Network Termination Device, NTD.

Cat-5/6 cabling, with "RJ-45" connectors, are the standard in the industry. They're tough, cheap, readily available and everyone knows how to work with them, terminate cables, test them and achieve reliable installations. At the moment, the per-port pricing for fibre interfaces is much higher than copper. SFP's, Small Format Packages for Fibre interfaces, are still relatively expensive in the retail market. In the future, I will concede, fibre will drive down in price and become the default wiring medium. Giving the price/performance evolution since 1999, this will take quite some time.

How is the industry standard, ethernet, universally preferred over VDSL, deployed?

• Cat-5a/6 cabling inside buildings supporting 100/1000Mbps ethernet to user devices
• 100Mbps & 1Gbps ethernet are specified to 100m over Cat-6 cabling.
• Fibre, as 2-fibre active ethernet, between floors and outside buildings
• usually two fibre links are run for redundancy and maintenance failover.

There are three sized installations that I think need to be specified:

• micro installs: 2-4 units
• small installs: 5-64 units
• large installs: over 65 units

For all these installs, I'm suggesting a new 1Gbps ethernet-NTD derived from the current GPON-NTD (2*UNI-V and 4*UNI-D). Done well, the external interface (GPON or Ethernet) would be a field-replaceable card. This would minimise part-count, firmware versions and allow simple management.

Up to 4-units, the existing GPON NTD with 4 UNI ports could be repurposed as a service multiplexor.
Each of the four UNI-D ports could be connected to an in-premise ethernet-NTD. Multiple VLANs, the critical low-level architectural element of the network, could be passed through the multiplexor to per-premise NTDs.

A single GPON-NTD can, I presume, support 2*1Gbps services and 2*100Mbps. Installations requiring additional 1Gbps services would need a second fibre and GPON-NTD, or the Body Corporate could pay for running direct fibre to each apartment/unit.

Small installs, up to 64, even 100 units, are all multi-floor. Only at the low-end will a single GPON fibre to the building be sufficient, suggesting active ethernet is necessary. The building gets a small version of a FSAM or a modest Fibre Distribution Area.

A network entry switch is needed in the basement, with dual ethernet fibre links to each floor, for reliability and in-place maintenance and upgrade.

Each floor needs one or more managed ethernet switches with dual fibre SFP's. Ethernet switches with 8-24 port capacity are readily available, highly reliable and have low port-costs. The cost of running conduit and Cat-5a/6 cable to each unit, mostly under 20m, is quite low. Getting through the wall into the apartment/unit may be the single biggest part of the job. This same conduit and access could be later upgraded to fibre quickly and cheaply.

The total amount of fibre run up the building cable shafts could be reduced to just two fibre-pairs with (cheap) 8-colour "Coarse WDM" SFP's. One colour per floor. This is light, small and easily installed and tested. Premade, fully-buffered fibre cables would make this task simpler and cheaper again.

Large installs, like large office networks, need to be purpose designed.
For a complex of 500-1,000 apartments, the aggregate upstream bandwidth will be that of a Fibre Serving Area, requiring DWDM ethernet. This fits in with the current network design and the upstream router/switches would be owned and managed by NBN Co.