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[Weaver]

From the job notes connected with last week's repairs post lightning strike I think it mentioned figures of 7.9 or 8.0 km for my lines. The website freemaptools comes up with a figure of 7.3 km for the by-road distance from me to the Broadford exchange. Is 8 km the true figure then?

So is this extra ~10% just accounted for by fractal wiggliness of the actual cable? Or it could be oversimplification by the mapping tool which does use many dozens of map points on the public road. What do we add as a general rule?

The cable is not buried when it's on the high ground, just lying on rocks.

Actually, I wonder if the freemaptools site only works in 2d - perhaps it doesn't account for the gain and loss in height, which would be something like a rise from roughly sea-level to 189m, and a fall back down to 112m according to freemaptools, and then my house is something like very roughly 10m above the road. But when we bring in our old friend Pythagoras, that height over such a long horizontal distance doesn't add anything much.

[Black Sheep]

Our RAT (Remote Access Test) system on BT circuits, or the TAMS (Test Access Matrix System) on LLU MPF's, measures the circuit for it's entirety from the actual test system based in the Exchange through to your socket.

All cable 'wriggles' accounted for. 

[Weaver]

@BlackSheep - I was in no doubt.

I just wonder what the typical wiggle factor is. I don't know how accurate my mapping tool is at all, plus anything about the lack of wiggle resolution in the mapping. If anyone is extremely bored, try mapping your own D-side if you know the route and the true line length.

If it's really ten percent, I wonder if buried cables can be made a lot straighter than cables laid on a very uneven surface - assuming that you don't have to follow some line such as a road that is itself all over the place. I'm talking about wiggles on a length scale of ~1m (say 0.5m - 5m) not > 5m.

Don't worry, I'm not going out late at night with the land rover to give it a huge tug.

[Black Sheep]

Ha ha ....... I don't think there is a 'Typical wiggle factor', Weaver ............ the cable just is what it is. 

[burakkucat]

Nearly five years ago, 17th June 2012 to be precise, I performed some TDR measurements on both my neighbour's circuit (with a G.993.2 service, 40/10 Mbps DS/US) and my own circuit (with a G.992.3 service, 4.3/0.9 Mbps DS/US).

I estimated that for both of us the length of our respective circuits from the pole-top DP to the NTE5/As were identical. Both our aerial drops are attached to the same bracket . . . I can open one of my windows and flick both cables with a broom-handle, to remove any build-up of winter snow, for example.

For the circuit with the G.993.2 service (neighbour) I measured (from the NTE5/A) ~384 m to the PCP and ~391 m to the Huawei SmartAX MA5603T DSLAM.

For the circuit with the G.992.3 service (my own) I measured (from the NTE5/A) ~384 m to the PCP and ~2168 m to the exchange based equipment.

All figures appear to be perfectly reasonable to me but not knowing the precise underground route of the cables involved, I have not compared it with map measurements. I would expect there to be a difference, with electrical measurements > map based measurements. Such a difference would be a measure Weaver's "wiggle factor" when applied in Suffolk. It will take in the excess cable length in joint boxes (or chambers), the initial drop of the DP tail, etc.

[Weaver]

My point about the typical wiggle factor is that there might indeed be more than one, leaving aside the geometry of roads. My mental picture is as follows: If your cable is buried in a neatly cut, ploughed trench, or in a duct then it will be 'straight', on a ~1m features’ length scale, but if it goes up and down over and around every rock then it will be a different story. The east side of Harris would be an extreme case, many areas where there is nothing but uneven rock and no soil other than in some cracks - quite startling, like being on another planet.

[burakkucat]

(b*cat nods.) Understood.

[renluop]

Our RAT (Remote Access Test) system on BT circuits, or the TAMS (Test Access Matrix System) on LLU MPF's, measures the circuit for it's entirety from the actual test system based in the Exchange through to your socket.

All cable 'wriggles' accounted for. 

14 years ago, soon after we moved house, we had some landscaping work done, that included a new drive way. it was pristine new, when a fault developed. So instead of ruining the work, we managed to have the cable routed back along the road, up the garden, and along the house wall. Would those tools take such alterations on board? I have my doubts.

[burakkucat]

Would those tools take such alterations on board? I have my doubts.

I would be very surprised if they didn't. Those systems will be looking at the electrical characteristics of the cable all the way to the NTE5/A, possibly even performing a TDR measurement.

Minor digression . . . The capacitive - resistive shunt across the pair, provided in the NTE5/A (or in the old LJUs), is designed to provide a known electrical termination of the circuit  -- even when no equipment (be it telephone, answering machine, modem, etc) is connected. The other purpose of that capacitive - resistive shunt is to form the AC "tap-off" point for the bell-wire.

[Weaver]

I think Burakkucat is correct but possibly only if BT's records about the physical cable segments are correct. And that's pretty likely to be the case any way. If they use time-domain reflectometry then it will be ridiculously accurate though.