rwatson at FreeBSD.org
Fri Oct 27 09:59:00 BST 2006
On Wed, 25 Oct 2006, khoa phan wrote:
> I want to ask You: when i configure my dummynet router with large delay
> time, then can packet loss happen? ,and can you show me how to increase
> network buffer size in dummynet router for overcoming it.
Each dummynet pipe is essentially a software queue with a set of delivery
properties, including bandwidth, delay, queue size, and packet loss rate.
Packet loss occurs for two reasons: (1) filling of the queue, and (2) as part
of probabilistic loss configured on the pipe. Since delay length affects how
long a packet remains in the queue, it directly affects how fast data can move
through the queue. You may want to google "bandwidth-delay product" for more
information on this topic. You can use the "queue" argument when configuring
a pipe to set the size in slots (packets) or in K.
Be warned that the whole issue of sizing queues/buffers in network stacks,
routers, etc, is non-trivial, so use large pipe sizes with caution. One
particular issue is that FreeBSD places an upper bound on the size of
in-flight packet data, and that if you start configuring many large pipes, you
may need to increase that limit. The main tuning parameter for this is
Robert N M Watson
University of Cambridge
More information about the Ukfreebsd