Active Queue Management (AQM) consists of embedding congestion
signals in the packet flow, which receivers use to instruct
senders to slow down when the queue is persistently occupied.
CAKE uses ECN signalling when available, and packet drops
otherwise, according to a combination of the Codel and BLUE AQM
algorithms called COBALT.
Very short latencies require a very rapid AQM response to
adequately control latency. However, such a rapid response tends
to impair throughput when the actual RTT is relatively long.
CAKE allows specifying the RTT it assumes for tuning various
parameters. Actual RTTs within an order of magnitude of this
will generally work well for both throughput and latency
management.
At the 'lan' setting and below, the time constants are similar in
magnitude to the jitter in the Linux kernel itself, so congestion
might be signalled prematurely. The flows will then become sparse
and total throughput reduced, leaving little or no back-pressure
for the fairness logic to work against. Use the "metro" setting
for local lans unless you have a custom kernel.
rtt TIME
Manually specify an RTT.
datacentre
For extremely high-performance 10GigE+ networks only.
Equivalent to rtt 100us.
lan
For pure Ethernet (not Wi-Fi) networks, at home or in the
office. Don't use this when shaping for an Internet access link.
Equivalent to rtt 1ms.
metro
For traffic mostly within a single city. Equivalent to rtt
10ms.
regional
For traffic mostly within a European-sized country.
Equivalent to rtt 30ms.
internet (default)
This is suitable for most Internet traffic. Equivalent to
rtt 100ms.
oceanic
For Internet traffic with generally above-average latency,
such as that suffered by Australasian residents. Equivalent to
rtt 300ms.
satellite
For traffic via geostationary satellites. Equivalent to rtt
1000ms.
interplanetary
So named because Jupiter is about 1 light-hour from Earth.
Use this to (almost) completely disable AQM actions. Equivalent
to rtt 3600s.
