The traffic generation rate can be modified by changing application properties. The two properties used by most applications as
1. Packet Size
2. Interarrival Time
And the generation rate would be
Generation Rate (Mbps) = (Packet size (bytes) * 8) / Inter arrival time (μs))
Reducing the packet size would decrease the generation rate. (In general, the packet size should not cross1460B in the application (which translates to 1500 Bytes after adding Transport & Network layer headers. If this is crossed then it would lead to fragmentation)
Reducing Inter-Arrival time would increase the generation rate.
Note that the generation rate should be less than or equal to the service rate for steady-state simulation, where the service rate is defined as the data rate supported by the Bottle-neck link.