Minimum And Maximum Pipe Precedence - D-Link NetDefendOS User Manual

Chapter 10: Traffic Management
In the illustration below the minimum precedence is 2 and the maximum precedence is 6.
Precedence 2 is taken as the best effort precedence.
Figure 10.5. Minimum and Maximum Pipe Precedence
Lowest Precedence Limits
It is usually not needed to have a limit specified for the lowest (best effort) precedence since this
precedence simply uses any spare bandwidth not used by higher precedences. However, a limit
could be specified if there is a need to restrict the bandwidth used by the lowest precedence.
This might be the case if a particular traffic type always gets the lowest precedence but needs to
have restricted bandwidth usage.
Precedences Only Apply When a Pipe is Full
Precedences have no effect until the total limit specified for a pipe is reached. This is true
because until the pipe limit is reached (it becomes "full") there is no competition between
precedences.
When the pipe is full, traffic is prioritized by NetDefendOS according to precedence with higher
precedence packets that do not exceed the precedence limit being sent before lower
precedence packets. Lower precedence packets are buffered until they can be sent. If buffer
space becomes exhausted then they are dropped.
If a total limit for a pipe is not specified, it is the same as saying that the pipe has unlimited
bandwidth and consequently it can never become full so precedences have no meaning.
Applying Precedences
Continuing to use the previous traffic shaping example, let us add the requirement that SSH and
Telnet traffic is to have a higher priority than all other traffic. To do this we add a Pipe Rule
specifically for SSH and Telnet and set the priority in the rule to be a higher priority, say 2. We
specify the same pipes in this new rule as are used for other traffic.
The effect of doing this is that the SSH and Telnet rule sets the higher priority on packets related
to these services and these packets are sent through the same pipe as other traffic. The pipe then
makes sure that these higher priority packets are sent first when the total bandwidth limit
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