that characterizes the loss of the link for individual splices and connectors by transmitting light pulses into a fiber and measuring the amount of light reflected from each pulse. STEP 3: ASSESS PoE OPERATION While adding DC resistance unbalance testing to the certification testing process can ensure support of two- and four-pair PoE applications for powering Wi-Fi APs, once the network goes live, there are various reasons why a PoE-enabled Wi-Fi AP may not receive sufficient power. On a PoE-enabled switch, power is typically allocated per port based on the device requirements. For example, a 24-port PoE-enabled switch may have a power budget of 740 W, enabling 30 W of PoE on each port. With such a wide variety of PoE devices residing on the network, it is unlikely that every connected device will need the full 30 W—a surveillance camera on one port might only need 12 W, while a high-throughput Wi-Fi 6 AP on another might need 25 W. Power allocation can be used to adjust port power and improve overall efficiency. The basic rule is that for a connected device to receive adequate power, the PoE class delivered via the switch port must be equal to or greater than the class of its connected powered device (PD). The total power required for all the devices cannot exceed the total power budget of the switch. Table 2 shows the various PoE classes for Type 1, Type 2, Type 3, and Type 4 PoE.
Confirming that the cable can support the application (e.g., 1000BASE-T) that the Wi-Fi AP requires is essential. While some simple testers will verify continuity, a true qualification tester uses specific standards-based measurements to test the cable across a range of frequencies to determine application support. Qualification testing is a quick and easy way to determine if existing Category 5e/Class D or Category 6/Class F can support 2.5 Gb/s or 5 Gb/s for Wi-Fi 5 devices (see sidebar). STEP 2: TEST THE NETWORK Once any cabling issues have been ruled out, the next step is to ensure the Wi-Fi AP is connected to the correct switch port and that the switch is configured properly. For example, links assigned to the wrong virtual LAN may not be able to communicate. Ethernet network switches use link layer discovery protocol (LLDP) or Cisco discovery protocol (CDP) to discover connected devices and advertise their capabilities. Network testers with the ability to leverage these protocols can display the switch name, port, advertised speeds, and assigned VLAN. Some testers even include a blink port light feature to help locate the connected switch port. An Internet Protocol (IP) ping test is also ideal for determining the accessibility of devices such as the wireless controller. Ping tests can also check for latency by determining the maximum round trip time through the network. Category 6A/Class FA cabling that supports 10 Gb/s Ethernet (i.e., 10GBASE-T) often also requires alien crosstalk testing, including power sum alien near-end crosstalk testing (PSANEXT) and power sum alien attenuation to crosstalk ratio far-end (PSAACR-F). This is due to higher-frequency signals causing interference from adjacent cables. Industry cabling standards recommend two Category 6A/Class FA connections to Wi-Fi 6/6E APs and four Category 6A/Class FA connections to Wi-Fi 7 APs. Depending on the project specification, Wi-Fi APs connected via fiber also necessitate Tier 1 certification testing with an optical loss test set (OLTS) that measures insertion loss on a link, or Tier 2 certification testing using an optical time domain reflectometer (OTDR)
“The basic rule is that for a connected device to receive adequate power, the PoE class delivered via the switch port must be equal to or greater than the class of its connected powered device (PD).”
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