Explanation
With PaaS providing a fully configured and managed framework, auto-scaling can be implemented to programmatically adjust resources based on the current demands of the environment.

With SDN, the filtering and forwarding capabilities and administration are separated. This allows the cloud provider to build interfaces and management tools for administrative delegation of filtering configuration, without having to allow direct access to underlying network equipment.
Firewalling and protocols are both terms related to networks, but they are not components SDN is concerned with.