FTTN: the Pair Gain System of the 21st century

I think it's fair to say that telecommunications in Australia has already been plagued with similar models of multi-technology mix setups — just like what NBN Co has proposed. And evidently, the system of pair gains in the copper network has been messing things and disadvantaging individuals for some time now and that's what NBN Co was designed to replace… but hold and behold — we're going to be plagued again for the coming few decades. And it's going to be our generation who will suffer through the wasted expenditure of NBN Co and be faced with the task of fixing up the crap and mess left behind by this Government.

Pair gain systems are widely spread in Telstra's copper network as a means of rapid deployment of telephone services in new estates or subdivisions in order to meet their Customer Service Guarantee (CSG) obligations. In short, pair gain systems is a way to multiply or increase the number of phone lines able to be provisioned to premises with only limited amount of copper to the exchange. Basically, this is much like a FTTN system…:

              56 kbps                           26 kbps
[Exchange] ------------ [Pair Gain System] ----------------[Premises]
             1000 mbps                          25 mbps
[FAN Site] -------------[Node] ----------------------------[Premises]

History repeats itself, as this ASCII illustration demonstrates
(just in case you're still on an antique pair gain system)

The Pair Gain Systems were great when they were first deployed! Phone services were up worked a-okay, deployed at a fraction of the cost and they were set up in lightning speed (compared with having to run new copper from the exchange). But guess what, the Dial Up revolution hit… and these pair gain systems were a bottleneck. While a regular dial up service was capable of up to 56Kbps… pair gains limited the speeds to appalling rates (as if it wasn't slow enough already):

Pair gain system Dial-up speed ADSL Compatible
No PGS Up to 56 Kbps No
2DPGS 26 Kbps No
4DPGS 9.6-14.4 Kbps No
SCaDS* 26 Kbps No
DCS20 26 Kbps No
RCM 28.8 Kbps No
RAM8 28.8 Kbps No

Source: http://whirlpool.net.au/wiki/PGS_Pair_Gain_Systems

* Fibre backhaul: hey, just like FTTN!

So, in summary… degraded performance but lower deployment costs compared with copper to the premises (CTTP). Sounds awfully like the comparison between Fibre to the Node and Fibre to the Premises. As if things didn't get worse, pre-CMUX pair gains were all unable to get ADSL services when that finally become available in Australia.

Later when the innovative RIM systems came along, dial up worked again without issues but still no ADSL available. It wasn't until CMUX finally came along, that Pair Gain systems were able to get a limited number of ADSL ports. And then still, there was no ADSL2+ available.

By mixing the technology of pair gain systems and copper to the premises (CTTP), chunks of Australians become disadvantaged simply because Telstra wanted to save some bucks. Just like by mixing the technologies of FTTN/B/dp, HFC and fibre to the premises (FTTP), Australians will be forever disadvantaged by the slow and expensive upgrade process required for each technology… while for FTTP, the only upgrades required are in at the Fibre Access Node and the end user's premises.

Having large amounts of active equipment (like an FTTN deployment) in the street will limit the ability to upgrade as demand grows. The task of upgrading field equipment is a huge expenditure and takes a lengthy process to complete.

I think we can say… pair gains have failed Australians once before; let not FTTN fail us again.


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