A counterintuitive failure
Bufferbloat is the problem of excessively large buffers in routers and modems that add huge delay under load. The intent of a big buffer is to avoid dropping packets, but congestion control relies on timely loss or marking to learn it should slow down. When a buffer holds seconds of data, the feedback arrives far too late, and latency balloons even though throughput stays high.
How it manifests
- A bulk download fills the oversized buffer, and every other packet waits behind it.
- Latency under load can jump from milliseconds to seconds, ruining interactive use.
- Loss based congestion control cannot react until the bloated buffer finally overflows.
- The link looks healthy on a throughput test yet feels broken for calls and games.
The fix is not simply smaller buffers, since those can underflow on bursty traffic. Modern solutions use active queue management schemes that keep the queue short by managing delay directly, dropping or marking based on how long packets have been waiting rather than on raw buffer occupancy. These keep latency bounded while still absorbing bursts, restoring responsiveness without sacrificing throughput.
Key idea
Bufferbloat is the latency disaster caused by oversized buffers that delay congestion signals, and the cure is delay aware active queue management that keeps queues short rather than just shrinking buffers.