Downstream drop, upstream fine

Back in August I switched from Plusnet to IDNet. Something I think I've mentioned before but not properly investigated is that my downstream throughput dropped. Overnight I went from around 65Mb/s on PN to around 55Mb/s on IDNet. My upstream throughput is the same at over 18Mb/s.

I don't have access to line stats but I've been pondering this recently and it seems a bit odd that I should see that big a drop on the downstream without any impact on the upstream. I vaguely recall that when I last check my sync I concuded that at 65Mb/s I was on the border of not getting full upstream speed.

Support say my line is performing too well to report it to OR but is 57/20 a 'reasonable' combination for a VDSL connection?

Edited by Andrue (Tue 28-Nov-17 14:40:24)

It is often that case that a full 20Mbps sync is possible on the upstream with an 18Mbps throughput with down stream values in the low to mid 50s.

I saw one set of figures this morning which were 63.8/20 sync and max attainable of 63/24 Mbps ... So, your drop on downstream from 65 to 55 due to noise or attenuation may have dropped the upstream too but it may still be above 20Mbps attainable.

What does your modem give for attainable ?

When changing providers the DLM is reset. This removes retransmission (if active) and often applies interleaving till retransmission returns. This causes a noticeable drop in downstream sync, but doesn't affect the upstream in the majority of cases.

A line with G.INP and a 3dB noise margin synced at 80Mb can drop as far as the low 60's after a DLM reset. This mainly affects those on Huawei cabinets, where DLM can have a much bigger impact on sync.

In reply to a post by j0hn83:

When changing providers the DLM is reset. This removes retransmission (if active) and often applies interleaving till retransmission returns. This causes a noticeable drop in downstream sync, but doesn't affect the upstream in the majority of cases.

A line with G.INP and a 3dB noise margin synced at 80Mb can drop as far as the low 60's after a DLM reset. This mainly affects those on Huawei cabinets, where DLM can have a much bigger impact on sync.

That could be it. If so it's taking its own sweet time to restore G.INP. I rebooted the modem earlier this month and it made no difference. Although I changed ISPs I didn't change the equipment in my house :-/