fttc stats

Come across some vdsl 2 stats you may be interested. Line length simulated (line loads) so cross talk / cable fill not accounted for but some interesting idea of how fast we can expect to go in future if Openreach were to adjust profiles.

Using vdsl 12a profile

at dslam - 80meg down, 50meg up.

800M away 78meg down, 48meg up

1.6km away 51meg down, 21meg up.

>3km - no sync.

Back to days of people not linking to information so others can review the information etc

VDSL2 at 3km does not equal NO SYNC, if should perform at longer distances similar to ADSL2+ and ADSL2 and ADSL.

Thus a 10km line with 5km D side and 5km E side, that struggles to see 160kbps sync now, could expect to see 2Mbps from a FTTC based VDSL2 solution, so long as CPE is allowed to auto negotiate down the compatible range of standards.

stats were from test equipment I saw running today and line length as shown by the modem, the loads were marked as 20db, 40db and 60db (although I have been advised true attenuation figures are not guaranteed as were not designed for vdsl) - perhaps it works out more as 4km rather than >3k?

In anycase these were real world results hence sharing them here rather than linking to a graph. At 60db the test unit attempted but would not hold sync.

I thought this might help us speculate on future speeds or capability with deployment from exchanges. That is all.

-OP

Curious.

What contention (if any) is considered standard with FTTx?

Simulated attenuation loading, and how about noise environment?

http://www.buckconsult.co.uk/fttx/BT8cProfilesVDSL2.jpg graph of the 8c profile that BT uses to meet the UK ANFP.

The comment about attenuation, is because you are using vastly different frequency ranges with VDSL and VDSL2, thus direct comparisons not possible. Plus no-one knows their attenuation to the cabinet.

BTW 3280 feet in a km

Also sounds like you were driving it in a pure VDSL (2 I hope) mode, and thus no negotiation fall back to slower modes once line length got to the point where VDSL2 frequencies were fully attenuated.

In reply to a post by MrSaffron:

Plus no-one knows their attenuation to the cabinet.

I'm sure my engineer's JDSU said (something like) signal loss 17dB? It also said, I know, approximate distance 0.6km. How does that fit in with graphs on the 8A? Openreach VDSL2 implememtation? Sync 39992kbps.

In reply to a post by Anonymous:

I thought this might help us speculate on future speeds or capability with deployment from exchanges. That is all.

The point being that the distance from the exchange is irrelevant. The DSLAM kicking out the VDSL2, (as MrSaffron queries, we hope you are talking about VDSL2, not VDSL), is at the FTTC cabinet.

As you mentioned, the UK ANFP governs FTTC here, and only allows BT to use a maximum frequency of 7.05MHz from the cabinets and 3MHz from the exchange, which is why we cannot get VDSL2 from exchange lines.

This means that we also have to follow a truncated 997 band-plan up to 7.05MHz only, which is what Profile 8c is all about, while profiles 8a, 8b and 8d extend to 8.5MHz, and profile 12a and 12b extend to 12MHz. Interestingly, the portion of band-plan 997 above 7.05MHz on all of those profiles is for UPstream data only.

This document by Ericsson has an alternative graph of VDSL2 vs Distance (page marked 43). The graph is titled "VDSL2 bit rates of different profiles. Real measurement in the presence of crosstalk from 20 VDSL2 systems." It includes profiles 8d, 12a, 17a, but all look to be most bound by the upstream service.

The crosstalk obviously has an effect there, because that shows considerably lower speeds. It shows 40Mbps for 200m or so, and is probably nearer to the kind of estimates that BT's checker is making.

I found another Openreach document that includes a 2009 primer for VDSL2, and includes infomation about the ANFP and band plans.

But that document, page 27 on, has an interesting piece about what Openreach has to do to make sure VDSL2 doesn't interfere with concurrent ADSL2+ signals fed from the exchange. Basically, they have to apply a "power shaping mask", which reduces the power of VDSL2 signal frequencies in the ADSL2+ frequency band; it reduces the signal in the cabinet down so it has the same level as would be expected for ADSL2+ signals that have arrived over the E-side wiring.

That means that, as the cabinet gets further from the exchange, the power mask is adjusted to reduce the power of the VDSL2+ signal more. But conversely, the cutoff frequency at the top-end of the mask can reduce as there is less expectation of the higher-frequency signals reaching so far.

This "power shaping" suggests that the speed of FTTC's VDSL2 isn't *purely* affected by the length of the D-side wiring (like we have always believed). The speed is also going to be affected by the power-shaping applied, and that depends on the length of the E-side wiring.

That part is all new to me... but from the references to ITU specs, isn't new to Telcos.

yes vdsl2.
I know fttc uses vdsl2 from the pcp dslam but if ever an exchange based solution was allowed the distance that you could hold out the higher speeds are interesting when considering whether it would be worth doing if we could.

Each time tested was using the same profile so intelligent alterations of profile to gain sync are unlikely to have been done but I fully accept other systems may well implement such things to extend reach.

I am not too technically minded compared to some on here so would this "shaping" of the profile around adsl / isdn etc frequencies make it possible for further profiles to be used (albeit with slightly less speeds than could otherwise be?) or would the reduced use of lower frequencies make this pointless for longer lines?

From what I have heard the BT option of 2meg uploads actually caps the sync rate not just throughput, so will the current profile (8c?) allow for greater speeds (assuming it is being capped) or is this really it until ofcom / BT agree new frequency plans?

BT's plans are a complete mystery.