The hierarchical layered model (Core, Distribution, Access) is a foundational Cisco design principle that provides scalability, performance, and manageability. It logically separates functions, making it easier to apply policies, contain failures, and grow the network. While the other options address specific needs (Wi-Fi, security, density), they are tactical decisions that should be made within the context of a sound overarching architecture.

In environments with dense obstructions like metal shelving, the radio frequency (RF) propagation is severely impacted. The original coverage area assumptions are likely invalid, requiring a reassessment of cell sizing (potentially needing more, lower-power APs) and careful channel selection to manage interference. Client device brand and aesthetics are not primary technical factors for solving this RF challenge.

For a business-critical, real-time application like VoIP, high availability is crucial. A single uplink from the access layer to the WAN edge represents a critical single point of failure. If that link fails, all users lose connectivity to the VoIP service and other network resources. While bandwidth and security are considerations, the lack of redundancy is the most glaring design flaw for service reliability.

The requirement explicitly mentions ‘seamless user mobility between buildings,’ which is a core function of a centralized wireless LAN controller (WLC) architecture. The WLC manages multiple access points, allowing client devices to roam between them without dropping sessions. While identity-based policies (option B) are related to the security part of the requirement, the primary service enabling the mobility is the centralized wireless control.

A collapsed core design is suitable for small networks but becomes a bottleneck as scale increases. The single device must handle both intra-VLAN distribution switching and high-speed core routing, leading to congestion. The most effective solution is to adopt a hierarchical design by separating the core (fast packet forwarding) and distribution (policy enforcement, aggregation) layers, which improves performance and scalability.

Cisco’s PPDIOO (Prepare, Plan, Design, Implement, Operate, Optimize) lifecycle defines a structured approach. After the ‘Plan’ phase (requirements, analysis), the ‘Design’ phase is where the logical and physical design is created. This phase translates requirements into specifications for devices, protocols, and topologies. Installation, operation, and budgeting are subsequent or parallel activities.

Redundant hot-swappable power supplies (RPS) provide power supply redundancy. If the primary internal power supply in the switch fails, the secondary (redundant) supply can immediately take over, preventing an outage for the PoE-dependent devices like phones and APs. StackWise provides control-plane redundancy, EnergyWise manages power usage, and airflow relates to cooling—none directly guarantee continued power delivery during a PSU failure.

Metro Ethernet (a type of Ethernet WAN or E-Line service) typically comes with a Service Level Agreement (SLA) that guarantees bandwidth, latency, and jitter. This makes it ideal for latency-sensitive VoIP traffic. Broadband Internet lacks these guarantees, Frame Relay is largely obsolete, and cellular is better suited for backup due to potential latency and data caps.

Using a structured, summarizable private IP address scheme (e.g., 10.0.0.0/8 subnetted hierarchically) allows for route summarization. This dramatically reduces the number of routes in the routing tables of core and distribution layer devices, which speeds up convergence, reduces memory/CPU overhead, and confines the impact of network changes—leading to greater stability and efficiency.

The hierarchical layered model (Core, Distribution, Access) is a foundational Cisco design principle that provides scalability, performance, and manageability. It logically separates functions, making it easier to apply policies, contain failures, and grow the network. While the other options address specific needs (Wi-Fi, security, density), they are tactical decisions that should be made within the context of a sound overarching architecture.0