Chapter 17 Traffic Shaping for FortiOS 5.0 : Traffic shaping methods : Type of Service priority : TOS in FortiOS
  
TOS in FortiOS
Traffic shaping and TOS follow the following sequence:
The CLI command tos-based-priority acts as a tos-to-priority mapping. FortiOS maps the TOS to a priority when it receives a packet.
Traffic shaping settings adjust the packet’s priority according the traffic.
Deliver the packet based on its priority.