Buffer Bloat

Buffer bloat is when your router can't satisfy all connections with the full speed because the buffers are full with data. It's a form of congestion and usually caused by upload (!) congestion because the ACK packets can't be sent fast enough.

A possible remedy is using QoS and traffic shaping as well as bandwidth limits.

Download/upload a large file and monitor your ping to a random server in the internet while you do that.

traffic-control smart-queue FixUploadBuf {
     upload {
         ecn enable
         rate 42mbit
         target 40
     }
     wan-interface eth2
 }

• Bufferbloat.net