D-Link NetDefend DFL-1660, User Manual

Page: 499 / 595

Specifying Precedences Within Pipes
When a pipe is configured, a Default Precedence, a Minimum Precedence and a Maximum
Precedence can be specified. The default precedences are:
• Minimum Precedence: 0
• Default Precedence: 0
• Maximum Precedence: 7
As described above, the Default Precedence is the precedence taken by a packet if it is not explicitly
assigned by a pipe rule.
The minimum and maximum precedences define the precedence range that the pipe will handle. If a
packet arrives with an already allocated precedence below the minimum then its precedence is
changed to the minimum. Similarly, if a packet arrives with an already allocated precedence above
the maximum, its precedence is changed to the maximum.
For each pipe, separate bandwidth limits may be optionally specified for each precedence level.
These limits can be specified in kilobits per second and/or packets per second (if both are specified
then the first limit reached will be the limit used).
Tip: Specifying bandwidth
Remember that when specifying network traffic bandwidths, the prefix Kilo means
1000 and NOT 1024. For example, 3 Kbps means 3000 bits per second.
Similarly, the prefix Mega means one million in a traffic bandwidth context.
Precedence Limits are also Guarantees
A precedence limit is both a limit and a guarantee. The bandwidth specified for precedence also
guarantees that the bandwidth will be available at the expense of lower precedences. If the specified
bandwidth is exceeded, the excess traffic falls to the lowest precedence. The lowest precedence has
a special meaning which is explained next.
The Lowest (Best Effort) Precedence
The precedence which is the minimum (lowest priority) pipe precedence has a special meaning: it
acts as the Best Effort Precedence. All packets processed at this precedence will always be
processed on a "first come, first forwarded" basis.
Packets with a higher precedence than best effort and that exceed the limit of their precedence will
automatically be transferred down into the lowest (best effort) precedence and they are treated the
same as other packets at the lowest precedence.
In the illustration below the minimum precedence is 2 and the maximum precedence is 6.
Precedence 2 is taken as the best effort precedence.
10.1.6. Precedences Chapter 10. Traffic Management
499