D-Link NetDefendOS User Manual page 785

• Use a fixed precedence
The triggering pipe rule explicitly allocates a fixed precedence.
• Use the DSCP bits
Take the precedence from the DSCP bits in the packet. DSCP is a subset of the DiffServ
architecture where the Type of Service (ToS) bits are included in the IP packet header.
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.
785
Chapter 10: Traffic Management