Link Layer Discovery Protocol - Media Endpoint Discovery (LLDP-MED) is a protocol used in PoE environments to enable devices to communicate their identity and power requirements to the PSE. The LLDP-MED protocol helps the PSE identify PDs and negotiate power requirements for those devices. This ensures that each PoE device receives the appropriate amount of power for operation and allows the PSE to accurately track its power budget. The Power budget is the total Power available to the PSE to supply all connected PDs and ensure they have adequate power to operate properly. Each connected PD will signal its power requirements in accordance with the IEEE 802.3 standards.
Discovery: When a device is connected to a network, it sends LLDP-MED packets to the switch or PSE. These packets contain information about the device, including its identity, capabilities, and power requirements.
Power Negotiation: Once the switch identifies the device, it can negotiate the power requirements with the device.
Monitoring: The LLDP-MED protocol allows for ongoing connected device monitoring . If a device's power needs change or if there are issues with the power supply, LLDP-MED can help in detecting and addressing these issues dynamically.
The LLDP-Med protocol plays an important part in the tracking of the total power budget for a PSE.
While PoE evolved to power networking devices like cameras, phones, and access points, etc., the specification was primarily released on Layer 2 switch ports. Cradlepoint is currently the only cellular router vendor supporting LLDP-MED on PoE WAN ports. Considering the scalability and future growth of your PoE network, and the rise of cellular as last mile primary transport, the ability to actively monitor the power budget to support a PD as your primary transport interface is critical.