Chapter 17 Traffic Shaping for FortiOS 5.0 : Traffic shaping methods : Shared policy shaping : Maximum and guaranteed bandwidth
  
Maximum and guaranteed bandwidth
The maximum bandwidth instructs the security policy what the largest amount of traffic allowed using the policy. Depending on the service or the users included for the security policy, this number can provide a larger or smaller throughput depending on the priority you set for the shaper.
The Maximum Bandwidth can be set to a value of between 1 and 16776000 kbit/s. The Web-Based Manager gives an error if any value outside of this range is used, but in the CLI a value of 0 can be entered. Setting maximum-bandwidth to 0 (zero) prevents any traffic from going through the policy.
The guaranteed bandwidth ensures there is a consistent reserved bandwidth available for a given service or user. When setting the guaranteed bandwidth, ensure that the value is significantly less than the bandwidth capacity of the interface, otherwise no other traffic will pass through the interface or very little an potentially causing unwanted latency.
See also 
Per policy
Shared traffic shaper configuration settings
All policies
Traffic priority
Per-IP shaping
Application control shaping
Enabling in the security policy
Type of Service priority
Differentiated Services
Tos and DSCP mapping
Traffic Shaper Monitor