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SNMP works by sending messages, called protocol data units (PDUs), to different parts of a network. SNMP-compliant devices, called agents, store data about themselves in Management Information Bases (MIBs) and return this data to the SNMP requesters.SNMP works by sending messages, called protocol data units (PDUs), to different parts of a network. SNMP-compliant devices, called agents, store data about themselves in Management Information Bases (MIBs) and return this data to the SNMP requesters. SNMP uses five basic messages (GET, GET-NEXT, GET-RESPONSE, SET, and TRAP) to communicate between the SNMP manager and the SNMP agent. There are variations to account for additional message types (see the six listed below).Data may be written usingData may be written using SNMP uses five basic messages (GET, GET-NEXT, GET-RESPONSE, SET, and TRAP) to communicate between the SNMP manager and the SNMP agent. The GET and GET-NEXT messages allow the manager to request information for a specific variable. The agent, upon receiving a GET or GET-NEXT message, will issue a GET-RESPONSE message to the SNMP manager with either the information requested or an error indication as to why the request cannot be processed. A SET message allows the SNMP manager to request a change be made to the value of a specific variable in the case of an alarm remote that will operate a relay. The SNMP agent will then respond with a GET-RESPONSE message indicating the change has been made or an error indication as to why the change cannot be made. The SNMP TRAP message allows the agent to spontaneously inform the SNMP manager of an "important" event.The GET and GET-NEXT messages allow the manager to request information for a specific variable. The agent, upon receiving a GET or GET-NEXT message, will issue a GET-RESPONSE message to the SNMP manager with either the information requested or an error indication as to why the request cannot be processed. A SET message allows the SNMP manager to request a change be made to the value of a specific variable in the case of an alarm remote that will operate a relay. The SNMP agent will then respond with a GET-RESPONSE message indicating the change has been made or an error indication as to why the change cannot be made. The SNMP TRAP message allows the agent to spontaneously inform the SNMP manager of an "important" event.