FTTN Technology

For the trials NBN Co is using Alcatel-Lucent ISAM 7330 VDSL2 Vectoring hardware. VDSL2 Vectoring delivers significant improvements to broadband performance. Extensive trials and commercial deployments by Alcatel Lucent have demonstrated capabilities of up to 100Mbps downstream and 40Mbps upstream on lines approximately 400m from the premises. Actual performance will vary based on a range of factors including the distance from the node, the quality of the copper, equipment used in the premises and the service providers’ own network.

Source: hwupgrade.it (under laboratory conditions favourable to DSL speed outcomes)

However, vectoring is significantly less effective when there are legacy access networks utilising the same cable bundle causing cross-talk and other forms of interference between the copper pairs in the cable bundle, or when different vendors are providing VDSL2 with vectoring over copper pairs in the same cable bundle from separate nodes. What this means is the vectoring is unlikely to be very effective if there are legacy access networks utilising copper pairs in a cable bundle.

So it will only be when the legacy systems are turned off that NBN will be able to ramp up VDSL2 with vectoring to its full capability, but let’s not forget that as more VDSL2 with vectoring customers come online connection speeds will drop due to cumulative noise effects within cable bundles and for many Australians this will mean a connection speed that is less than stellar and far lower than what FTTP would have provided.

FTTN delivers vastly different performance levels depending on location

While FTTP is essentially unaffected by distance, the FTTN achievable speed is all about distance.

  • At 100m, FTTN could deliver about 100Mbps
  • At 500m, that drops to about 50Mbps
  • At 1km, it drops to about 25Mbps

The distance is the actual copper length, a typical FTTN system would deliver maximum speeds of less than 25Mbps, which is in line with the NZ experience of 13Mbps average.

VDSL / xDSL Fault Analysis & Location

There are at least 11 connectors through the entire link, and the most prone to problems is the drop wire section.

Step-1: Customer Side Test

  • To place the xDSL tester at red line 2 (above Figure) before the Terminal splitter. If normal, indicates the xDSL line is fine; Otherwise, there is faulty line.
  • To place the xDSL tester at red line 3 before the xDSL MODEM. If normal, indicates the Terminal splitter is fine; Otherwise there is a problem in the Terminal splitter.

Step-2: Twist Pair Line Test

Line fault can be divided into two categories:

  • Too much attenuation in the line, such as:
  • The line is too long;
  • The quality of the line is poor;
  • Short circuit;
  • Open circuit;
  • The fittings are corroded;
  • Poor contact point;
  • Excessive bridge taps
  • Interference or too much noise in the line
  • Signal cross-talk between pairs;
  • Radio interference;
  • Electromagnetic interference household appliances;
  • Motor or electromagnetic interference caused by electric locomotive;
  • The weather causes interference cables (such as lightning)

The failure is often caused by a number of factors listed above.

The xDSL line loop resistance index should be less than 900Ω, if the actual line length is much less than the line length that is estimated based on the line loop resistance, there is poor contact on the line, the joint oxidation and other high impedance fault.

The voltages which should be present on a telephone line when it rings, when it is off hook, and when it is on hook etc.

Extracts from Australian Post Office Specification 1104 Issue 2 (March 1971)

Audible Signals for Australian Telephone Network Statement of Planning Objectives

7. Ringing Current

(IV) Ringing current has a nominal frequency of 17 Hz.

The actual frequency of ringing current from automatic exchanges shall be between 15 Hz and 27.5 Hz.

Ringing current fed from P.M.B.X. switchboards may have a frequency not exceeding 50 Hz.

This of course was derived from a transformer in the rectifier that supplied supply the 50V for the switchboard.

(Vi) The voltage measured at the subscribers line terminals in the exchange shall not be less than 75 V with the ring source fully loaded.

The no load voltage shall not rise above 100 V.

Adequate protection should be included in the current feeding equipment to ensure reasonable safety to personnel.

It appears that in earlier years that 33 Hz Ringing Machines were used

An extract from Telephony 3 states Paper 4 Re Issued 1951

The standard ringing frequency is 16-2/3 c/s although some earlier machines produce ringing current of 33 c/s.

The nominal DC voltage on a POTS was 48V (24 secondary cells @ 2V) but the actual open circuit line voltage was around 52V (24 x 2.2V). The specified acceptable range was something like 46V-54V.

The ring voltage was 80V-90V rms, 17Hz non-sinusoidal and, as stated above, this is superimposed on the DC line voltage. AS/NZS 60950.1 (I think Annex M) should give you some indication of the various ring voltages and cadences used around the world.

Note that the DC line voltage from in-premises or near-premises equipment (PABXs, FTTP ONTs, etc.) may be as low as 24V because the line loop is usually very short. Ring voltage will also be reduced.