Answer: The Subscriber Modules (SMs) are tiered to your capacity needs. Four models of the PMP 450 SM will be available at the same throughput levels as PMP 430 was: 4, 10, 20, or uncapped (up to 55) Mbps. A software license key upgrade can be purchased to move between the various levels. The cost difference in moving between levels is the same whether you purchase the model directly or update it in the field.