4170t-ams.ib.rev0.doc Page 7 of 14 17/10/2007
SNMP
What Is It?
SNMP stands for Simple Network Management Protocol. It is an application layer protocol for managing IP
(Internet Protocol) based systems. SNMP enables system administrators to manage system performance, and to find
and solve system problems. SNMP runs over UDP (User Datagram Protocol), which in turn runs over IP.
Three types of SNMP exist: SNMP version 1 (SNMPv1), SNMP version 2 (SNMPv2) and SNMP version 3
(SNMPv3). It is not the intention here to discuss the differences between various versions, only to bring attention to
the fact that IRT Electronics modules, fitted with SNMP capability, use SNMPv1.
An SNMP managed network consists of three key components: Network Management Systems (NMS), agents, and
managed devices.
An NMS is the console through which the network administrator performs network management functions, such as
monitoring status (e.g. alarm states) and remote controlling, of a set of managed devices. One or more NMSs must
exist on any managed network. Generally the NMS is a computer running third party SNMP control software. There
are a number of third party SNMP software applications currently available on the market.
An NMS polls, or communicates with, an agent. An agent is a network management software module that resides in
a managed device. An agent has local knowledge of management information and translates that information into a
form compatible with SNMP. The agent, therefore, acts as an interface between the NMS and the managed devices.
The NMS sends a request message, and control commands for the managed devices, to the agent, which in turn
sends a response message, containing information about the managed devices, back to the NMS.
A managed device contains an SNMP agent and resides on a managed network. Managed devices collect and store
management information and make this information available to NMSs using SNMP.
Managed device agent variables are organised in a tree structure known as a Management Information Base (MIB).
Within the MIB are parameters pertaining to the managed device. An Object Identifier (OID) number within the
MIB defines the managed device type. This is a unique number specific to the model of managed device. Other
information relating to the device is also stored, information such as alarm states, controllable settings, etc. The MIB
tree is organised in such a way that there will be no two MIB files with conflicting placements.
Normally an NMS polls an agent for information relating to the MIB in a managed device to be sent back to the
NMS. When certain conditions are met within the MIB, such as major alarm conditions, for example, the agent
automatically sends what is known as a trap to the NMS without any prompting from the NMS. This allows
automatic notification of a predetermined event.
NMS
NMS
IP
Network
MIB
SNMP Agent
Protocol Engine SNMP Agent
MIB
SNMP Agent
Protocol Engine SNMP Agent
MIB
SNMP Agent
Protocol Engine SNMP Agent
SNMP Block Diagram
