BBR, the new kid on the TCP block

It's almost irresponsible to write an article on this topic in 2017 without explicitly mentioning bufferbloat or network-scheduling algorithms like CoDel designed to address it. If you really want to understand this article, read up on those first.

https://en.wikipedia.org/wiki/CoDel

CoDel is different from the packet scheduling algorithm even though both fight bufferbloat in different ways. CoDel is a congestion control algorithm for controlling what happens when outgoing buffers start overflowing. This is on a lower level than TCP and happens to any type of packet. The scheduling algorithm, like VEGAS or BBR, controls the transmit rate of only the TCP protocol.

When packets are being sent over the wires, the TCP scheduling algorithm (usually CUBIC, VEGAS, RENO, or now BBR) will send out packets until the parameters they monitor indicate the downstream device is about to overload. Then they will back off slightly to prevent packets from being lost. These TCP transmit strategies tend to either monitor packet loss rate or round trip time, sometimes both. What they do with these two parameters determines the biggest differences between the packet sending algorithms.

CODEL comes into affect when the scheduling algorithm decides it can't send out packets quickly enough without losing them, and they build up on local buffers. This can happen with TCP but also other internet protocols.

Something most people don't know is that without a scheduling algorithm like BBR,VEGAS, or RENO, you can send out packets at interface speed. In simpler protocols like UDP you need to do your own packet scheduling. Otherwise your machine will send out packets at interface speed until they are mostly dropped by the first slower link. This is why TCP has scheduling algorithms, they're all an attempt to monitoring the end to end link speed from A to B you can achieve without losing data.

Edit: BBR is a new TCP scheduling algorithm to fight buffer-bloat at the TCP level. Since the majority of internet traffic is TCP, wide adoption would cause a big improvement. TCP scheduling only affects outgoing packets, so its important to get this into Windows and Linux so we can get the full benefit of having buffer-bloat reduction on both ends. I'm looking at MS here because they're the last major OS running an aggressive and buffer-bloat causing TCP algorithm.

So, to be clear: BBR only applies to the edge nodes (the client and the server) whereas CoDel and other AQM are (mostly) for the routers in between, especially bottle-neck points, right?