Confused by my line stats versus real performance

[#1]

I'm trying to get my head around my line stats and to understand whether my connection (fttc 80/20) is working as well as it should, or whether there's still potential for improvement.

• Putting my phone number into btwholesale's checker gives a VDSL range of 69.7-80 clean or 67.7-80 impacted, and a maximum observed speed of 80/20 earlier this month.
• This seems to tally with what I'm seeing in DSLStats, with my modem consistently syncing at 79,999/19,999 and a max attainable of around 82,400/23,300 (I realise the sync is capped but I'm just recognising that there's a margin of headroom there). Downstream SNRm is consistently pinned at 5.8dB.
• G.INP is enabled on the downstream. Depth 8, INP 52, INPRein 1. This is interleaving low, correct?
• The Plusnet member centre is listing my "Current Line Speed (Download): 78Mbps".
• The most recent GEA test for my line (Saturday) found no RF ingress, no REIN, no crosstalk, no interference, no service impact, and no home wiring problem, a rate assessment of "Very Good", and an estimated line length of 270m. This, I'm assuming, should put me in the "clean" rather than "impacted" range?

My interpretation of this is that my connection should, in theory, be working at about as close to the maximum speed as is reasonable to expect, but I'm not getting those speeds in reality.

I appreciate that this is #firstworldproblems and that a certain level of loss for network overheads is to be expected, but speed tests are giving just 68Mbps (+/- 0.5Mbps) and 10-12Mbps of overheads sounds excessive to me, it's 15%. This is the same whether it's the Ookla test, the Thinkbroadband one, or BTw's own.

Doing the diagnostics on the BTW checker states that the "IP Profile for your line is 70.61 Mbps". Am I right in guessing that this IP Profile is what's bottlenecking my line, and whose responsibility is it to fix - BTWholesale or Plusnet? Will DLM get its act together eventually and fix it it automatically, or does it need intervention?

[#2 · Accepted solution]

I've had a look into this and I think the throughput you're seeing is about right. 

It'd be Openreach's responsibility to correct an IP profile through their diagnostics team. From experience it seems that BT Wholesale have as much control over the remote settings of a fibre line as we do (which is limited).

Generally, faults are passed to Openreach's diagnostics team either by an engineer requesting it or if the stars align (Basically a KBD* test has to fail with a very particular outcome for the fault report to automatically end up there)

KBD is a series of tests that we run as part of testing a fibre service, one of those tests includes a GEA test.

Your modem's in sync at 79.9mbps but there's high retransmission(a form of error correction)* enabled by the dynamic line management (DLM) at the cabinet which will bring the IP profile to around 90% making that correct at 70.61mbps.

*Ignore the 'profile name' on the GEA test we've logged on your account that says there's interleaving and no mention of retransmission. The timestamp of this particular data on the GEA test was 2021-01-31 17:00:00, the remainder of the information on the GEA test should be correct though.

I've checked a different system called RRT that gives more up to date profile data and it's showing: "Downstream: 0.128M-80M5dB with Retransmission (High). Upstream: 0.128M-20M with no error protection"

Your throughput will always sit a meg or two below the IP profile due to the overheads you've mentioned.

I hope this helps.

[#3]

That's great, thanks for the informative reply.

So basically it's a DLM thing - if the stars align and my line stays error- and resync-free it might eventually decide that high retransmission is overkill and my IP profile might subsequently improve a bit, but that's a wait-and-see-job? I've no downstream ES or resyncs since I started monitoring my line stats, aside from me messing around rebooting the router, so I'm hopeful it might get better  

I shall leave it alone and wait and see!

[#4]

No problem @ChrisFox Yeah it's a wait, hope and see thing unfortunately. 

At least your line's doing better than my own, I've actually got the same profile "Downstream: 0.128M-80M5dB with Retransmission (High). Upstream: 0.128M-20M with no error protection" but a sync speed of 48.554mbps...

(Fairly long line to the cabinet!)