Understanding queue size

[jeremie le-hen]

Hi,

ipfw(8) manual page, section "TRAFFIC SHAPER (DUMMYNET) CONFIGURATION" tells:

     queue {slots | sizeKbytes}
           Queue size, in slots or KBytes.  Default value is 50 slots, which
           is the typical queue size for Ethernet devices.  Note that for slow
           speed links you should keep the queue size short or your traffic
           might be affected by a significant queueing delay.  E.g., 50 max-
           sized ethernet packets (1500 bytes) mean 600Kbit or 20s of queue on
           a 30Kbit/s pipe.  Even worse effect can result if you get packets
           from an interface with a much larger MTU, e.g. the loopback inter-
           face with its 16KB packets.

I understand that if the queue size is too large, then it will imply large
delays. But what if the queue is too short ? Does anyone can point me a
detailed document which talks about queues ? Or maybe it exists a simple
general rule explaining all this stuff...

Regards,
-- 
Jeremie aka TtZ/TataZ
jeremie.le-hen at epita.fr