What would cause reducing upload speeds?

I've been with Zen for years without issues. I assume this would apply to any ISP but what can cause reducing upload speeds over time?

If I unplug the router from the BT socket the connection resets and it's showing the max speed on the Zen test page ie 40mb down and 8+ mbit up.

Leave it a few days and it's down to 40mbit down but only 2 or 3 mbit up.

Last week it was as bad as 24 mbit down and 1 mbit up.

Zen support don't seem to get there's an issue as they just do the test and it says 'everything is fine' but it clearly isn't as this same line was happily doing 6 to 7 mbit upload speeds for ages and it's gone stupid at some point and I noticed it only when the backup was running and I was doing other web browsing or streaming. It wasn't very good all of a sudden.

What can fault without registering a fault at Zen? There is only packet loss if the upload side is occupied ie when doing a back up for example. Then it happens. Otherwise it's not showing as anything than just slow and stuck at a new low max speed.

Any ideas on how to work out where the fault lies so I can at least say to them 'It's X what's broken'?

I’d start by replacing the router.

If it was the line, DLM would have kicked in, and wouldn’t spring back up so swiftly just by unplugging and then reconnecting the router.

Is the router connection speed (sync) dropping or just the throughput?

It's both. The Zen speed tests show the product speed I assume. When I do a speed test I generally get a proportion of that speed. So it often shows 40mb down so I generally get 36. 8 or 9mb up and I get 7 or 8. It remains roughly 10% off what the product speed is for download but the upload falls off.

I don't have a laptop to plug into the modem itself now.

Edited by serichards (Mon 07-Aug-23 09:48:18)

In reply to a post by Zarjaz:

I’d start by replacing the router.

If it was the line, DLM would have kicked in, and wouldn’t spring back up so swiftly just by unplugging and then reconnecting the router.

Interesting. I'm hoping Zen will realise this as I've told them twice now unplugging and plugging back in seems to just reset back to higher speeds.

Ran the speed test via Zen again. 40 mb down and 2.2 mb up. Yesterday it was 40mb down and 8mb up. It's just weird.

Edited by serichards (Mon 07-Aug-23 09:47:40)

Another option I could think of … something on your LAN side swamping the upload,

Unplug everything, disable wifi, then just use I single wired device for a few hours .. see how that goes

In reply to a post by serichards:

It's both. The Zen speed tests show the product speed I assume. When I do a speed test I generally get a proportion of that speed. So it often shows 40mb down so I generally get 36. 8 or 9mb up and I get 7 or 8. It remains roughly 10% off what the product speed is for download but the upload falls off.

I don't have a laptop to plug into the modem itself now.

Forgive me if I've got this wrong, but it's not clear from your answer if you have checked the synch speeds shown on the router, as you only talk of speed tests.

In reply to a post by Zarjaz:

Another option I could think of … something on your LAN side swamping the upload,

Unplug everything, disable wifi, then just use I single wired device for a few hours .. see how that goes

Not that. I can see on the Asus router page what the activity is like.

In reply to a post by burble:

In reply to a post by serichards:

It's both. The Zen speed tests show the product speed I assume. When I do a speed test I generally get a proportion of that speed. So it often shows 40mb down so I generally get 36. 8 or 9mb up and I get 7 or 8. It remains roughly 10% off what the product speed is for download but the upload falls off.

I don't have a laptop to plug into the modem itself now.

Forgive me if I've got this wrong, but it's not clear from your answer if you have checked the synch speeds shown on the router, as you only talk of speed tests.

I haven't done that as there is no easy way to do it. I'm assuming the Zen check is showing me the sync speed.

I can't interrogate the ADSL modem easily to find out what it thinks. The asus router plugged into the modem doesn't seem to have that information either that I can see.

Maybe if you post model of modem someone might know how to view it.