When uploading, download speed is slow.

[#1]

Hi,

Bit of an odd one. For a while now, whenever I am uploading something (such as when using dropbox or backblaze), my download speed slows to a crawl. When I stop using one of these services, my download speed goes back to normal consistently.

Apart from ... not using backblaze or dropbox... is there anything you can do to fix this?

Many thanks!

[#2]

Which router are you using?

The 2704n is particularly known for causing 'bufferbloat', although saturating the upload will always affect the download speed to some extent whichever router you use.

[#3]

@gwp 

As @JayG has said, this is called bufferbloat and is caused by the need to 'handshake' whilst uploading and downloading. Some routers can cope with this better than others, the Hub Zero is known to be particularly bad.

You could probably  get some improvement with a better router but the  best way to fix it is to increase your bandwidth by upgrading to fibre if it's available to you.

[#4]

---

@gwp wrote:

... is there anything you can do to fix this?

---

Yes !.

Use a router with upload "QoS" (Quality of Service) buffering on your DSL connection, and set the upload bandwidth to about 85% of your usual upload speedtest result.  I did that for years when I was on ADSL and it makes a noticeable improvement in download speed and responsiveness (on all devices) - despite losing 15% of your available upload speed !.

I still use upload "QoS" even after upgrading to 80/20 fibre, as it gives a measurable improvement in latency - especially when doing a bandwidth draining download such as a Steam game update.

Check that you are using the fastest variant of ADSL available on your phone line.

Use the  BT BROADBAND AVAILABILITY CHECKER  to find what speeds of ADSL you can select, and then check that your modem is connecting correctly to the fastest variant. i.e. make sure you are connected with ADSL2+ (also known as "G.992.5").

[#5]

Hello @gwp,

I am sorry to hear this is happening, I have increased the noise margin from 3db to 6db which should take effect in the next hour. Please let us know if this makes a difference.

[#6]

Hi all,

Thank you for all your advice! I think the noise ratio change helped! Could you explain what that is, please, @SammyM?

Many thanks!

[#7]

Hi @gwp,

I'm glad to hear that your connection is now looking better. Please keep an eye on things over the next few days and let us know if you experience any further problems. It's likely that there has been an increase in the level of interference on the line, which is why we had to raise the SNR margin to allow the line to cope with the extra interference. As this may be caused by many different things, it's not possible to say exactly what led to this.