* B (Dynamic real-time change):SDN must adapt dynamically as network demands and application requirements evolve.
* E (Integration of device context):Understanding device-level status, capabilities, and resource availability allows controllers to make informed decisions, reducing visibility gaps.
Other options explained:
* A: On-demand growth is a business benefit but not related to visibility/performance gaps.
* C: Reverting to legacy behaviors undermines SDN benefits.
* D: Peer-to-peer controllers help scale, but not directly tied to visibility gaps.

A modular, scalable network design aims to:
* Localize faults
* Reduce impact radius of failures
* Enable automated fault detection and recovery
The primary operational driver is to reduce the need for manual intervention during failures, which translates to:
* Faster recovery times
* Consistency in troubleshooting
* Improved service reliability
While minimizing app downtime (B) is a goal, it is a result of reducing human-required failure recovery.
Option C is a business process goal, and D is an architectural challenge, not an operational driver.
This aligns with CCDE v3.1's "Network Architecture Principles" for building operationally resilient networks.

IaaS, PaaS, and SaaS each offer a progressive layer of abstraction after that. IaaS abstracts away the physical compute, network, storage, and the technology needed to virtualize those resources. PaaS goes a step further and abstracts away the management of the operating system, middleware, and runtime.
https://www.ibm.com/topics/iaas#:~:text=IaaS%20abstracts%20away%20the%20physical,system%2C%
20middleware%2C%20and%20runtime.