GE PACSystems RXi User Manual

Chapter 12. PROFINET Network ManagementGFK-2816F August 2015 22912.2 LLDPThe PNC implements the Link Layer Discovery Protocol (LLDP). A PROFINET IO-Supervisoror other network host may use LLDP to discover the PROFINET network.12.2.1 Overview of LLDPThe Link Layer Discovery Protocol is an IEEE standardized protocol used by network devicesto advertise their identity and capabilities and receive that information from physicallyadjacent link layer peers. LLDP data packets are sent by devices from each of their interfacesat fixed intervals. The LLDP packets are multicast and are not forwarded by networkswitches.Each LLDP packet consists of one LLDP Data Unit (LLDPDU). Each LLDPDU is a sequenceof Type-Length-Value (TLV) structures.LLDP Data Unit ContentsChassis ID TLV structure (mandatory, always first)Port ID TLV structure (mandatory, always second)Time to Live TLV structure (mandatory, always third)Optional Structures (any number of these, in any order)...End of PDU TLV (mandatory, always last)12.2.2 LLDP OperationThe LLDP agent in the PNC multicasts LLDP messages to the network at 5 second intervals,or when a change occurs in any of the local data that is delivered within the LLDP message.The LLDP messages are transmitted from each external port that is connected to a network.