[AusNOG] ADSL2+ line sync data

[Paul Wallace]

The dulcet tones of wisdom come from maturity and usually maturity alone Matt!






On 12/09/2013, at 12:52 PM, "Matt Perkins" <matt at spectrum.com.au<mailto:matt at spectrum.com.au>> wrote:

I think just taking distance into account is very simplistic view of things. Im not sure what state the copper is in the UK. However in Australia there are other things to consider other then distance.

Joints. - The number of joints in an adsl loop dramatically decrease SNR and increase loss. The type of joint is also of interest. Insulation displacement is far better then non soldered pin strip for example.

Cable type / gauge. - Cable type and gauge varies greatly. There is far less loss on higher gauge cable. However most of the time gauge changes at every joint this produces all sorts of nasty results from impedance mismatches to standing waves.

Bridge Tap - xDSL's worst enemy and Telecom stalwart from the 1970-80's bridged taps are responsible for most of the SNR problems on xDSL.  I remember pulling these things out for a living when attempting to reduce the BERT on Auspac and X25 services back in the 80's (now im showing my age)  These things are going to be the biggest problem for the new VDSL/FTTN environment. Technicians paid per completed service will not have a lot of incentive to go find and remove these so the rule of thumb will be. "Does it work at any speed, Yes. Good next job" . Just as it is now.

Customer premiss cabling - Although this isn't some time's our problem as ISP's it becomes our problem through support man hours and unhappy customers, How many customers have you had a discussion with about that old K-Mart non twisted pair 20m extension cord and those old disused 5 parallel sockets (more bridged tap's). It cant be my extension cord it worked yesterday.

<rant>
My experience is the people working in this space, maintaining the Telstra CAN (or customer area network) have very poor understanding of these issues and the ones that do dont have the time to care when they apply the pizza delivery pay model to these guys. None of this will change, price pressure and time frame's will make a network that needs serious TLC even worse. I have a customer that has been waiting 7 months for copper that was damaged during a road works project to be replaced. 3G for 7 months. Good luck with that.

VDSL has it's place. In buildings - however we spend serious time going to customers sites in buildings only to find that a technician with a time pressure was there that morning and stole what they thought was a spare pair for a phone service. Just because they could hear no dial tone on it. No dial tone it must be free.

Welcome to the brave new - old world of data over copper.
</rant>



 On 12/09/13 12:17 PM, Paul Brooks wrote:
A recent Ofcom (UK) report has a very interesting chart of ADSL2+ line speeds:
Ofcom Infrastructure Report 2012 Update
http://stakeholders.ofcom.org.uk/market-data-research/other/telecoms-research/broadband-speeds/infrastructure-report-2012/
http://stakeholders.ofcom.org.uk/binaries/research/telecoms-research/infrastructure-report/Infrastructure-report2012.pdf
Figure 4 on page 11:
<ATT00001.png>
This chart is effectively the result of the ADSL line-sync/attenuation curve combined with the increasing area of circles of increasing radius around the exchange - and demonstrates very clearly why so many people get low ADSL2+ line speeds.
(Exercise for the reader - work out how VDSL2 would be any different)

Also scatter-plots of sync-speed with line-length, as per Figure 8 from another UK report:

<ATT00002.png>
Now every DSLAM network operator can put together similar charts - but I'm not aware of any stats for Australian networks, apart from the heat maps put out by iiNet and the adsl2exchanges.com.au<http://adsl2exchanges.com.au> site, which aren't quite what I'm looking for.
For all you DSLAM operators - I would be very interested in putting together similar charts for the Australian networks, to see how our copper loop network varies from the UK network. If anyone is willing to share data or statistics, I'm very interested in pulling together similar Australian charts - on a non-identified, aggregated, anonymised basis if you wish.
Please contact me off-list - thanks.
Paul.






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