The queue limit defaults define the default number of datagrams in each queue.

The default high limit is 20 datagrams.

The default medium limit is 40 datagrams.

The default normal limit is 60 datagrams.

The default low limit is 80 datagrams.

In general, it is not a good idea to change the default queue sizes.
@@ 2
Weighted fair queuing is dependent on encapsulation.

When the router initializes, the Cisco IOS checks the encapsulation type specified for each interface.

Serial interfaces using HDLC, LAPB, PPP, Frame Relay, or SMDS encapsulation are candidates for fair queuing.

Serial interfaces are further categorized by bandwidth (link speed).

Fair queuing is enabled, by default, on serial interfaces with the proper encapsulation type operating at 2.048 Mbps (E1) or less.

Fair queuing is not enabled on serial interfaces using X.25, or compressed PPP as the encapsulation type.

LAN interfaces and serial lines operating at E3 or T3 speeds are also not available for fair queuing.
@@
