Head scratching

Recently I have lost over 8 Mbps from the download which so far cannot be resolved or explained.

I was seeing an upload of 66.5 Mbps all nice and stable. Then when service restored after an incorrect cease and other issues, the line returned in the low 50s and finally stabilised at 57 Mbps

Two visits from BT OR - the last for well over 3 hours has not resolved it. Port changed, drop wire switched, DLM reset, new face plate ... nothing can pull it up.

Speed test from BT, TBB and Ookla all show the same figures (allowing for differences in methodology).

Line stats:

DSL uptime: 1 Days, 2 Hours 50 Minutes 53 Seconds
Data rate: 17.14 Mbps / 68.42 Mbps
Maximum data rate: 17143 / 70483
Noise margin: 6 dB / 5.4 dB
Line attenuation: 0 dB / 16.5 dB
Signal attenuation: 0 dB / 16.5 dB
VLAN id: 101
Modulation: G_993_2_ANNEX_B
Latency type: Fast Path

Latency is nice and low at 7ms

With a Max Achievable of 70.5 and sync of 68.4 I would expect to see somewhere around 65 - much the same as I was seeing before however, 57 is way down from that .

Any thoughts on what to try next ...

Has the line been up long enough for G.Inp to be reapplied?

When my line was reset I lost about 6Mbps for a few days, then one night G.Inp got reactivated and I recovered the lost speed. After a few weeks, DLM started to drop the SNRM and eventually settled on 3dB which added a little more to the data rate.

You are probably on "Interleaved", despite what those stats say. We need to see the D: figures from them and also the delay: figures.

The firmware common to many modems and modem/routers reflects only the upstream interleave depth being zero in that "Latency type" line, and ignores the far more important downstream.

As has been said, G.INP will probably kick in soon, it had previously been activated. G.INP would result in delay zero and downstream interleaving (D: ) probably 8 down, 0 up. If downstream D: is in the hundreds or higher that is definitely interleaved and delay non-zero.

Unfortunately on the Business Smart Hub futher details cannot be found! There are 20,000 lines of an event log, but nothiong of relevance there. Since te problems it has been up for around 5 weeks so g.inp would have kicked in by now.

First thing you should do is check the IP profile.

https://windows.mouselike.org/be/index.asp?DoAction=...

Interesting:

The current Downstream BRAS rate is: 59.77 Mbps
The current Upstream BRAS rate is: 20 Mbps

Which suggests it may well be stuck!

Definitely an IP profile issue.
No DLM profile should have an IP profile 87% of the sync speed.

Have been unable to get that detail - for some reason te BT tester has been giving me an error with something like "Performance Tester disabled for TAP3 support ... "

Have a call scheduled for Monday - conference and meetings until then!

In reply to a post by j0hn83:

Definitely an IP profile issue.
No DLM profile should have an IP profile 87% of the sync speed.

IIRC that's what you get when G.INP is active. The reason being that the sync rate reported to the ISP's radius server is considerably below the sync reported in the user's modem(/router). As clearly seen on AAISP where that report is listed in the log.

This has been discussed a few times on these forums.

The IP Profile is correctly calculated from that reduced sync. Whether it is Openreach reporting low to BT Wholesale, or BT Wholesale applying a reduction for some reason, I never got to the bottom of.

At the time AAISP were questioning both my modem (despite results from three different ones) and in effect my sanity. As far as they were concerned the radius log was gospel.

Fastpath or Interleaving it should be 96.8%
Retransmission Low should be 96.7%
Retransmission High should be between 91-92% of the sync speed.

There's a few random lines where the lines stats shows ReTx Low yet the IP profile is 91-92% (what ReTx High should be).

That's what happened with your line, I recall discussing it before.
You should have had an IP profile of 96.7% but it was sticking at 91-92%.

It should never be 87% of the sync speed.