Bufferbloat

Bufferbloat is high latency in packet-switched networks caused by excess buffering of packets. Bufferbloat can also cause packet delay variation (also known as jitter), as well as reduce the overall network throughput. When a router or switch is configured to use excessively large buffers, even very high-speed networks can become practically unusable for many interactive applications like Voice over IP (VoIP), online gaming, and even ordinary web surfing.

Some communications equipment manufacturers placed overly large buffers in some of their network products. In such equipment, bufferbloat occurs when a network link becomes congested, causing packets to become queued in buffers for too long. In a first-in first-out queuing system, overly large buffers result in longer queues and higher latency, and do not improve network throughput.

The bufferbloat phenomenon was initially described as far back as in 1985. It gained more widespread attention starting in 2009.

An established rule of thumb for the network equipment manufacturers was to provide buffers large enough to accommodate at least 250 ms of buffering for a stream of traffic passing through a device. For example, a router's Gigabit Ethernet interface would require a relatively large 32 MB buffer. Such sizing of the buffers can lead to failure of the TCP congestion control algorithm, causing problems such as high and variable latency, and choking network bottlenecks for all other flows as the buffer becomes full of the packets of one TCP stream and other packets are then dropped. The buffers then take some time to drain, before the TCP connection ramps back up to speed and fills the buffers again.

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