Forwarding classes allow you to group packets for transmission. Based on forwarding classes, you assign packets to output queues. The forwarding class plus the loss priority define the per-hop behavior (PHB in DiffServ) of a packet. J-series Services Routers support eight queues (0 through 7). Forwarding classes are mapped one-to-one with these queues. By default, queues 0 through 3 are mapped to forwarding classes—best effort, assured forwarding, expedited forwarding, and network control. Queues 4 through 7 are not mapped to forwarding classes. To use queues 4 through 7, you must create custom forwarding class names and map them to the queues. For more information, see Forwarding Class Queue Assignments.