The industry-standard best practice for designing a WLAN to ensure optimal performance is to use RF modeling and predictive survey software. This process involves importing floor plans, defining environmental materials (e.g., drywall, concrete), and specifying customer requirements for coverage, capacity, and device types. The software then simulates RF propagation, allowing the designer to strategically place access points to meet these requirements precisely. This proactive, data-driven approach is superior to reactive methods or simple rules-of-thumb, as it accounts for the unique characteristics of the physical environment and ensures the design is optimized before any hardware is installed.

A. Placing an AP in every room is a brute-force approach that often leads to excessive co-channel and adjacent-channel interference, which degrades network performance, even with RRM.

C. Mist SLEs are powerful tools for monitoring and troubleshooting an existing network's performance. They are not intended to be the primary tool for initial network design and AP placement.

D. Placing APs based on a fixed distance is an unreliable rule-of-thumb that fails to account for RF attenuation from walls, furniture, and other obstacles, leading to a suboptimal design.

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1. Juniper Mist, "Wi-Fi Design Guide": This guide outlines the entire WLAN design process. It states, "The first step in any Wi-Fi design is to understand the requirements of the network... Once the requirements are understood, the next step is to create a predictive design using a tool such as Ekahau Pro or Mist Wi-Fi Planner." (Section: "The Design Process", Page 4). This directly supports using RF modeling software as the correct methodology.

2. Juniper Networks TechLibrary, "Mist APs Overview": In the deployment best practices section, the documentation emphasizes planning. "Before you deploy your APs, you should perform a site survey to determine the optimal placement for each AP. A site survey helps you to identify potential sources of interference and to ensure that you have adequate coverage throughout your facility." This reinforces the need for a planned design process over arbitrary placement. (Section: "Deployment Best Practices").

3. Juniper Open Learning, "JNCIA-MistAI (JN0-250) Courseware": The official course material for the exam details the WLAN design lifecycle. The "Planning and Design" module explicitly covers the use of predictive modeling tools to create a design based on customer-defined coverage and capacity requirements, identifying this as a critical step for a successful deployment. (Module: "WLAN Design and Configuration").