You configure class of service (CoS) when you need to override the default packet forwarding behavior of a J-series or SRX-series device—especially in the three areas identified in Table 247.
Table 247: Reasons to Configure Class of Service (Cos)
You can use either J-Web Quick Configuration or a configuration editor to configure CoS. This chapter contains the following topics. For more information about CoS, see the JUNOS Class of Service Configuration Guide.