D-Link DFL-260 Product Manual - Page 453
Minimum and Maximum Pipe Precedence, Lowest Precedence Limits
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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. 453