Seemingly capped at 40/10

I have an exchange only BT so called "Infinity 1" VDSL2 service with a dream installation i.e. new property install 3 years ago, no extension wiring, BT NTE5a with MK3 filter, ZyXEL VMG8924-B10A router.

I have confirmed that our DLM profile was reset at last contract renewal - we have only had BT as ISP.

We have a Huawei DSLAM in the FTTC in our rural exchange car park (I assume BT are planning sell this exchange in the future).

During out last contract renewal (£5/mo for unlimited Infinity 1) the BT rep' was proud to announce that our "service would now be up to 55mbps". As can be seen from below the Downlink appears capped at 40mbps.

Any advice how to achieve the full throughput for our circuit would be greatly appreciated.

Router stats are below.

====================================================================================
VDSL Training Status: Showtime
Mode: VDSL2 Annex B
VDSL Profile: Profile 17a
G.Vector: Disable
Traffic Type: PTM Mode
Link Uptime: 12 days: 8 hours: 6 minutes
====================================================================================
VDSL Port Details Upstream Downstream
Line Rate: 4.346 Mbps 39.998 Mbps
Actual Net Data Rate: 4.318 Mbps 39.999 Mbps
Trellis Coding: ON ON
SNR Margin: 5.8 dB 10.4 dB
Actual Delay: 0 ms 0 ms
Transmit Power: - 3.6 dBm 13.1 dBm
Receive Power: -22.0 dBm -9.6 dBm
Actual INP: 0.0 symbols 48.0 symbols
Total Attenuation: 0.0 dB 23.7 dB
Attainable Net Data Rate: 4.258 Mbps 49.782 Mbps
====================================================================================
VDSL Band Status U0 U1 U2 U3 U4 D1 D2 D3
Line Attenuation(dB): 7.3 38.9 N/A N/A N/A 18.6 48.9 75.0
Signal Attenuation(dB): 7.3 38.8 N/A N/A N/A 21.0 48.5 78.6
SNR Margin(dB): 5.7 5.8 N/A N/A N/A 10.4 10.4 10.5
TX Power(dBm): -14.8 -4.0 N/A N/A N/A 11.3 7.8 -1.6

Get BT to put you on a 55m profile. Your attainable is 49.

Is it that easy?

It seems too reasonable, all too often I speak with BT rep's and get a "computer says no" response!

If that is the case, I'll try to speak with a UK call centre on Monday.

Don't forget to have the exact figures to hand to tell them:-

Line Rate: 4.346 Mbps 39.998 Mbps
SNR Margin: 5.8 dB 10.4 dB
Attainable Net Data Rate: 49.782 Mbps

The downstream SNR Margin is important. It shows the line is being held back, to the extent shown by the Attainable Rate.

Edited by RobertoS (Sat 20-May-17 22:55:02)

Have you resynched the router since renewal?

Good point.

Don't worry I shall have.

Disappointingly though historically they have not known what I am talking about, they just read from a script and run line tests.

Sorry, yes.

Renewal was in December 2016, with HH5a (27mbps downstream).

I changed this to SmartHub (type A) which gave an improvement (33mbps downstream) due to more compatible Huawei DSLAM SoC.

Two months ago I changed again to ZyXEL VMG8924-B10A (latest stock firmware) with Broadcom 63168 SoC. This improved to 37mbps downstream, then when DLM had stabilised capped at ~40mbps.

In reply to a post by DeanWade:

Is it that easy?

It seems too reasonable, all too often I speak with BT rep's and get a "computer says no" response!

If that is the case, I'll try to speak with a UK call centre on Monday.

I can't advise on BT. My only involvement with BT is the phone line and have had trouble getting an Engineer out to repair a crackly line. Although once I had no dial tone and sent an email when my Mum was alive about her having a dicky heart and no emergency phone line and they sent an engineer on a Saturday morning and it was sorted straight away.

Its best to try and deal with a British call centre but tricky to get in touch with one, the best time is normal during the week daytime to call up and if you can try and get a direct number to a UK call centre.

Then it could be an Openreach DLM "banding" cap.

To check, run the BT Wholesale Performance Test. (Ignore all the red instructions, just say you've done them. We don't need to know these results).

At the bottom of the initial results page click Further Diagnostics. Put your landline phone number in when asked. When it comes up with the graphs and text boxes, what is the IP Profile speed?

If it is very close to 38.71 or 38.67 then it is not banded.

If it is more like 36.anything then it is banded and you really will have a CS problem. let us know what it shows and we can advise further.

Edited by RobertoS (Sun 21-May-17 00:10:40)