When the kernel has several packets to send out over a network
device, it has to decide which ones to send first, which ones to
delay, and which ones to drop. This is the job of the queueing
disciplines, several different algorithms for how to do this
"fairly" have been proposed.

If you say N here, you will get the standard packet scheduler, which
is a FIFO (first come, first served). If you say Y here, you will be
able to choose from among several alternative algorithms which can
then be attached to different network devices. This is useful for
example if some of your network devices are real time devices that
need a certain minimum data flow rate, or if you need to limit the
maximum data flow rate for traffic which matches specified criteria.
This code is considered to be experimental.

To administer these schedulers, you'll need the user-level utilities
from the package iproute2+tc at <ftp://ftp.tux.org/pub/net/ip-routing/>.
That package also contains some documentation; for more, check out
<http://linux-net.osdl.org/index.php/Iproute2>.

This Quality of Service (QoS) support will enable you to use
Differentiated Services (diffserv) and Resource Reservation Protocol
(RSVP) on your Linux router if you also say Y to the corresponding
classifiers below. Documentation and software is at
<http://diffserv.sourceforge.net/>.

If you say Y here and to "/proc file system" below, you will be able
to read status information about packet schedulers from the file
/proc/net/psched.

The available schedulers are listed in the following questions; you
can say Y to as many as you like. If unsure, say N now.

source code:

net/sched//