LEDBAT

LEDBAT stands for Low Extra Delay Background Transport. It is a congestion control algorithm designed for the internet that aims to minimize latency while still utilizing available bandwidth. Traditional congestion control protocols like TCP NewReno can sometimes lead to increased bufferbloat, where network buffers become excessively full, causing high latency for interactive applications like video conferencing and online gaming. LEDBAT addresses this by actively probing for free bandwidth without causing undue delays.

The core idea behind LEDBAT is to operate with a "desired" backlog, which is a target number of packets in the network path. The algorithm adjusts its sending rate based on the difference between the actual measured round-trip time and a baseline round-trip time. If the actual round-trip time is significantly longer than the baseline, it indicates congestion, and LEDBAT reduces its sending rate. Conversely, if the round-trip time is close to the baseline, it signals available bandwidth, and LEDBAT increases its sending rate.

LEDBAT is particularly beneficial for background traffic, such as large file transfers or backups, which can coexist with interactive traffic without significantly impacting its performance. It achieves this by being a "polite" congestion control algorithm, meaning it yields bandwidth to more aggressive protocols when congestion occurs. This makes it a valuable tool for improving the overall quality of experience on the internet by reducing latency for sensitive applications. Several operating systems and network applications have incorporated LEDBAT or similar low-delay congestion control mechanisms.