Subject: Significance of Minimum Policed Unit?

From: Kam Lee <[email-masked]>
Date: Mon, 15 Feb 1999 12:42:34 -0800

In RFC 2210 (see excerpt below), the Minimum Policed Unit (m) is meant to be
used by intermediatenetwork nodes to determine the amount of bandwidth
compensation for link-level header overhead. 

Are there any other uses of this parameter elsewhere under the IntServ
framework?

thanks,
kam

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"The minimum policed unit parameter [m] should generally be set equal to the
size of the smallest packet generated by the application. This packet size
includes the application data and all protocol headers at or above the IP
level (IP, TCP, UDP, RTP, etc.). The size given does not include any
link-level headers, because these headers will change as the packet crosses
different portions of the internetwork. The [m] parameter is used by nodes
within the network to compute the maximum bandwidth overhead needed to carry
a flow's packets over the particular link-level technology, based on the
ratio of [m] to the link-level header size. This allows the correct amount
of bandwidth to be allocated to the flow at each point in the net. Note that
smaller values of this parameter lead to increased overhead estimates, and
thus increased likelihood of a reservation request being rejected by the
node. In some cases, an application transmitting a low percentage of very
small packets may therefore choose to set the value of [m] larger than the
actual minimum transmitted packet size. This will increase the likelihood of
the reservation succeeding, at the expense of policing packets of size less
than [m] as if they were of size [m]."

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From: Steven Berson <[email-masked]>
Date: Tue, 16 Feb 1999 10:33:41 -0800 (PST)

> Are there any other uses of this parameter elsewhere under the IntServ

Kam,

I am not sure I understand what you mean.  Basically the minimally
policed unit is used to try to guarantee payload bandwidth rather than
(payload+headers) bandwidth.  So, when used properly, you can get at
least the payload bandwidth you reserve.

Steve