Part 3: Understanding the MIB (Management Information Base)
Each snmp element manages specific objects with each object having specific characteristics. Each object/characteristic has a unique object identifier (OID) consisting of numbers separated by decimal points (e.g., 1.3.6.1.4.1.2682.1). These object identifiers naturally form a tree as shown in the below illustration. The MIB associates each OID with a readable label (e.g., dpsRTUAState) and various other parameters related to the object. The MIB then serves as a data dictionary or codebook that is used to assemble and interpret SNMP messages.
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| Figure 2. The branch of the MIB object identifier tree that represents managed elements used by DPS Telecom equipment. |
When an SNMP manager wants to know the value of an object/characteristic, such as the state of an alarm point, the system name, or the element uptime, it will assemble a GET packet that includes the OID for each object/characteristic of interest. The element receives the request and looks up each OID in its code book (MIB). If the OID is found (the object is managed by the element), a response packet is assembled and sent with the current value of the object / characteristic included. If the OID is not found, a special error response is sent that identifies the unmanaged object.
When an element sends a Trap packet, it can include OID and value information (bindings) to clarify the event. DPS remote units send a comprehensive set of bindings with each Trap to maintain traditional telemetry event visibility. Well-designed SNMP managers can use the bindings to correlate and manage the events. SNMP managers will also generally display the readable labels to facilitate user understanding and decision-making.
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