We also were confused by this initially and had call with a Cambium employee to clear this up.
DLBL and ULBL are the actual rate limits. DLBR/ULBR is the Burstable. Each is expressed in Kbps. This is the behavior if both are set of course. Otherwise you can get away with only DLBR being set if you are not picky about burst.
For example, this is what we set for a 3Mbps down by 1Mbps up package:
Wireless_3Mb_1Mb Cambium-Canopy-DLBL := 3000
Wireless_3Mb_1Mb Cambium-Canopy-DLBR := 3072
Wireless_3Mb_1Mb Cambium-Canopy-ULBL := 1000
Wireless_3Mb_1Mb Cambium-Canopy-ULBR := 1024
The DLBL/ULBL is the data rate (3Mbps) and the DLBR/ULBR is the burstable. So the customers gets 3MB down as his data rate, burstable to 3072 down. So when you run the initial speed test, should see the burst to 3072 and then it settle down to 3000.
You can also set the bucket fill rate and all that. The Cambium white paper has an overview of the theory:
Details are also in the PMP 450 Series Configuration Guide downloadable in the Support -> Downloads section (search for Burst Allocation to find the section in the guide).