LEDBAT

Low Extra Delay Background Transport (LEDBAT) is a way to transfer data on the Internet quickly without clogging the network.^[1] LEDBAT is invented by Stanislav Shalunov;^[2][3] and is used by Apple for software updates and by BitTorrent for most of its transfers.^[4] LEDBAT is estimated to carry 13–20% of Internet traffic.^[4][5] LEDBAT is a delay-based congestion control algorithm that uses all the available bandwidth while limiting the increase in delay^[2][6] LEDBAT works measuring one-way delay and using changes in the measurements to limit congestion that the LEDBAT flow itself induces in the network.

Design goals

LEDBAT congestion control has the following goals:^[2]

1. Use all available bandwidth, and to maintain a low queueing delay when no other traffic is present,
2. Limit the queuing delay it adds to that induced by other traffic, and
3. To yield quickly to standard TCP that share the same bottleneck link.

Implementations and deployment

The two main implementations are uTP by BitTorrent and as part of TCP by Apple. BitTorrent uses uTP for most traffic and makes the code available under an open-source license.^[7] Apple uses LEDBAT for Software Updates so that large software downloads to Mac OS X computers and iOS devices do not interfere with normal user activities; Apple also makes the source code available.^[8]

References