Uploading Slows Down Download Speed Considerably

[ML18]

Whenever I notice anything uploads, It totally destroys download speeds. Something as simple as viewing a website can take a minute to view or sometimes just fails. This can be from uploading a video on WhatsApp to backing up files on cloud storage.

I would just like to know if this is normal on a ADSL connection or is it just me?

 

[PhireSide]

So what you need to know is that for transmits, which are usually TCP, each packet that gets sent gets acknowledged and returned to the sender to confirm that the packet has been received before the next packet gets sent. So, for every megabyte of data you upload, a small portion gets downloaded as part of the TCP/IP system to confirm that the data arrives intact at the other side.

What could be happening is that your line has errors on the uploads, thereby causing a lot of traffic down asking for retransmits by the receiver. Some Googling leads me to believe that the TCP overheads can be around 6% of upload, or 9% total bandwidth.

If you have a slower line, which is common with ADSL connections, it can make a significant difference to your line speed.