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Physical and Logical Infrastructure Requirements

Chapter Description

In this sample chapter from CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide: Designing & Implementing Cisco Enterprise Wireless Networks, you will learn how to determine physical infrastructure requirements including AP power, cabling, switch port capacity, mounting, and grounding. You will also learn how to determine logical infrastructure requirements such as WLC/AP licensing requirements based on the type of wireless architecture.

This chapter discusses the following topics:

Physical Infrastructure Requirements: Powering an access point with Power over Ethernet (PoE) has several variants, including delivering power directly from a switch or through a power injector. However, PoE itself comes in several flavors that have cabling infrastructure dependencies. This section discusses the main types of PoE, including PoE, PoE+, UPoE, and UPoE+, and the types of cables that support them. In addition, as modern 802.11 standards begin to push beyond 1Gbps, traditional Ethernet connections over twisted pair cable is no longer enough to support the maximum performance capabilities of the access point. This section discusses the improved performance characteristics of mGig and the network requirements necessary. This section also discusses AP mounting and grounding strategies.

Logical Infrastructure Requirements: This section discusses the logical elements of a wireless network, such as the communication flow of the CAPWAP control and data channels as they traverse the network, and their implications on the underlying physical infrastructure. In addition, this section discusses controller and AP licensing mechanisms.

This chapter covers the following ENWLSD exam topics:

  • 2.1 Determine physical infrastructure requirements such as AP power, cabling, switch port capacity, mounting, and grounding

  • 2.2 Determine logical infrastructure requirements such as WLC/AP licensing requirements based on the type of wireless architecture

The focus of wireless network design often revolves around the RF aspects of the deployment—and indeed, as discussed throughout this book, RF design is the foundation of any successful wireless network and almost always involves a robust site survey. However, there are key infrastructure components that are just as important in any wireless design exercise. These are generally grouped into two major classes: the physical infrastructure components and logical infrastructure components.

The physical infrastructure includes components of the physical networking gear. This involves the physical gear itself, as well as how the access points are cabled, powered, mounted, and even grounded. This design aspect goes far beyond just the access points and the controller. For example, if a switch is used to deliver PoE to an AP, the switch must be able to accommodate the power requirements of the AP. If it cannot, either the AP will not power on or certain capabilities (such as secondary radios) will not work.

Additionally, the reachability of the APs over standard Ethernet cabling becomes a design criterion as distances from the switch grow and as higher data rates are used. When the existing cable plant cannot support the distances demanded by the placement of APs, suboptimal AP placement may be used, which in turn may lead to poor RF coverage. Understanding the design requirements of the physical infrastructure is a crucial aspect of developing a successful wireless design.

The second infrastructure aspect is the logical network—in other words, the path the communication flows take through the network, regardless of the underlying physical infrastructure. Controller-based wireless networks use CAPWAP (Control And Provisioning of Wireless Access Points), both as a control channel as well as to encapsulate client data traffic, effectively tunneling client traffic directly from the AP to the controller, and vice versa. This gives the logical appearance that the APs and controller are Layer 2 adjacent, when in reality they may be traversing many hops of the underlying physical network. Understanding the behavior and function of these logical elements introduces important considerations when developing the infrastructure side of the wireless design.

This chapter focuses on these two infrastructure aspects, beginning with the physical infrastructure and followed by the logical infrastructure.

“Do I Know This Already?” Quiz

The “Do I Know This Already?” quiz allows you to assess whether you should read this entire chapter thoroughly or jump to the “Exam Preparation Tasks” section. If you are in doubt about your answers to these questions or your own assessment of your knowledge of the topics, read the entire chapter. Table 4-1 lists the major headings in this chapter and their corresponding “Do I Know This Already?” quiz questions. You can find the answers in Appendix D, “Answers to the ‘Do I Know This Already?’ Quizzes and Review Questions.”

Table 4-1 “Do I Know This Already?” Section-to-Question Mapping

Foundation Topics Section


Physical Infrastructure Requirements


Logical Infrastructure Requirements


  1. An access point has been deployed with full features, including dual radios and hyperlocation. The AP requires 38W of power. Which of the following Power over Ethernet capabilities should you recommend be used?

    1. PoE

    2. PoE+

    3. UPOE

    4. UPOE+

  2. A group of new Wi-Fi 6 (IEEE 802.11ax) APs has just been installed in a building to replace the older Wi-Fi 5 (802.11ac wave 1) APs. What is a design consideration you need to be aware of when deploying the physical infrastructure?

    1. Mounting of the new APs to reflect changes in the 802.11ax RF radiation pattern.

    2. An increase of power will be required. The switch will need to be upgraded to support either UPOE or UPOE+.

    3. The number of Wi-Fi 6 APs required will be less than the older APs thanks to better performance and coverage patterns.

    4. The switch connected to the APs may need to be upgraded to support mGig.

  3. For security reasons, the building facilities team abides by a policy that no devices (APs included) may be visible from the office floor. As an alternative, the network team is looking to deploy the APs above the suspended ceiling. What should they be aware of?

    1. Positioning APs above the ceiling will result in significant RF degradation, so a new site survey may be required.

    2. This configuration is not supported by Cisco.

    3. Specialized mounting brackets will be needed.

    4. The APs should be positioned as close to the T-bar rails as possible.

  4. When deploying higher throughput wireless technologies in Local mode, what design aspect must be considered related to possible oversubscription of the physical infrastructure?

    1. Uplink capabilities of the access switch should be considered.

    2. Physical connections between the access switch and AP should be considered.

    3. Performance of the backbone network connecting to the controller should be aligned with overall wireless performance demands.

    4. Performance capabilities of the controller should be considered.

    5. All of the above.

  5. What interfaces on a physical controller (such as the WLC 5520) are used to communicate to key services such as ISE and CMX? (Choose two.)

    1. The service port

    2. The Management Interface

    3. The virtual port

    4. Any LAN interface port on the controller

    5. The AP-Manager interface

  6. Which Cisco wireless licensing model involves pooling of licenses?

    1. Right-to-Use (RTU) licensing

    2. Perpetual licensing

    3. Term licensing

    4. Product Activation Key (PAK) licensing

    5. Smart Licensing

Foundation Topics

2. Physical Infrastructure Requirements | Next Section

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