SNMP is based on the manager/agent model consisting of an

SNMP manager, an SNMP agent, a database of management

information, managed SNMP devices and the network protocol.

The SNMP manager provides the interface between the human

network manager and the management system. The SNMP agent

provides the interface between the manager and the physical

device(s) being managed.

The SNMP manager and agent use an SNMP Management

Information Base (MIB) and a relatively small set of

commands to exchange information. The SNMP MIB is organized

in a tree structure with individual variables, such as

point status or description, being represented as leaves on

the branches. A long numeric tag or object identifier (OID)

is used to distinguish each variable uniquely in the MIB

and in SNMP messages.

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.