Which of the following is NOT an advantage of Software-defined Networks (SDN) over traditional networks?

The fundamental architectural shift in Software-defined Networking (SDN) is the move from a distributed control plane to a centralized one. In traditional networks, each network element (router, switch) operates autonomously, running its own control plane protocols to make independent forwarding decisions. SDN centralizes this intelligence into a controller, which has a global view of the network. The network elements in the data plane are no longer autonomous; they receive forwarding instructions from the controller. Therefore, the autonomous operation of network elements is a defining characteristic of traditional networks, not an advantage of SDN.

B. Decoupling of control plane from data plane: This is the core principle of SDN and its primary advantage, enabling centralized control, programmability, and abstraction of the underlying network infrastructure.
C. Centralized controller operations: Centralizing network control simplifies management, allows for consistent policy enforcement, and enables more sophisticated traffic engineering, making it a key benefit of SDN.
D. Global view of network's state: The centralized controller's comprehensive, network-wide view allows for optimal path computation and rapid response to network changes, a significant advantage over the limited, local view of devices in traditional networks.

1. Kreutz, D., Ramos, F. M. V., Veríssimo, P. E., Rothenberg, C. E., Azodolmolky, S., & Uhlig, S. (2015). Software-Defined Networking: A Comprehensive Survey. Proceedings of the IEEE, 103(1), 14–76.

Page 15, Section II-A: "In traditional networks, the control and data planes are vertically integrated... This coupling makes networks notoriously difficult to manage... SDN advocates the separation of the control and data planes." This text directly supports that decoupling (B) is a core SDN tenet and contrasts it with the autonomous nature of traditional devices (A).

Page 18, Section II-C: "The network control plane is logically centralized, which offers... a programmatic interface to the network, and a global view of the network." This supports that centralized operations (C) and a global view (D) are defining advantages.

2. Nokia (2021). Nokia Network Services Platform (NSP) Solution Card.

Page 2, "Benefits" section: The document describes the NSP (a carrier SDN platform) as providing "Centralized policy control and network automation to simplify operations across multivendor IP, optical and microwave networks." This directly validates centralized control (C) as a primary advantage of Nokia's SDN implementation.

3. McKeown, N., Anderson, T., Balakrishnan, H., Parulkar, G., Peterson, L., Rexford, J., Shenker, S., & Turner, J. (2008). OpenFlow: Enabling Innovation in Campus Networks. ACM SIGCOMM Computer Communication Review, 38(2), 69–74. https://doi.org/10.1145/1355734.1355746

Page 70, Section 2: "An OpenFlow Switch has... a flow table, and a secure channel that connects the switch to a remote controller. The controller manages the switch by adding and removing flow-entries from the flow table." This foundational paper on an early SDN protocol shows that network elements are not autonomous (A) but are directly managed by a central controller (C).