Minimum And Maximum Pipe Precedence - D-Link DFL-260E User Manual

10.1.6. Precedences
Chapter 10. Traffic Management
Figure 10.5. Minimum and Maximum Pipe Precedence
Lowest Precedence Limits
It is usually is 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 bu 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 don't 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 specified in the
pipe's configuration is exceeded. Lower priority packets will be buffered and sent when higher
priority traffic uses less than the maximum specified for the pipe. The buffering process is
sometimes referred to as "throttling back" since it reduces the flow rate.
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