The summary.
UPLOAD MATTERS MORE THAN PEOPLE THINK
Calls, backups, sending files and anything hosted locally all depend on it.
Poor call quality is frequently a saturated upload, not a slow download.
Schedule backups and large transfers outside working hours.
TEST PROPERLY
On a cable, with other devices idle, at several times of day, more than once.
Testing over wireless measures the wireless, not the connection.
THE FOUR QUESTIONS THAT LOCATE A SLOW CONNECTION
One device or all? Everything or one destination? All the time or certain times? Wired as well as wireless?
Each answer points somewhere different.
BEFORE BUYING MORE BANDWIDTH
Establish what is consuming it. Managing demand is usually cheaper and frequently sufficient.
FOR A BACKUP CONNECTION
It must not share the same failure. Two services over the same physical route fail together.
Test failover before you need it.
WHEN REPORTING A FAULT
Have restarted, tested on a cable, and recorded results with times.
Intermittent faults are dismissed without evidence.