Communication by SNMP protocol

SNMP is a protocol that allows the SNMP manager (admin, PROMOTIC app) to control SNMP agent by transmitting the SNMP messages. SNMP messages is a packet sent via Ethernet UDP/IP on port 161. This message can be used to read or set parameter values from/into the agent.

The SNMP protocol exists in three versions 1, 2, 3. The 2 version contains additional authentication and the 3 version encryption. The most commonly used version of the SNMP protocol is the version 2. Unfortuantely this version is not in any way standardized and therefore the devices using such communication are often incompatible.

For this communication in the PROMOTIC system can be used:

PmSNMP - Driver for communication via the SNMP protocol


OID (Object Identifier):

Each value in the SNMP is identified by numeric identifier OID. OID consists of a sequence of whole numbers separated by full stops (e.g. "").

Each valid OID must begin with numbers "1.3...".

Each device supporting the SNMP should return at least the values of following objects:

- "" = Time period since device power on.
- "" = Text description of the device.

MIB database (Management Information Base):

Each SNMP agent has the list of all his parameters saved in the MIB database that contains the name, OID, data type, read/write capability and short description for each parameter. However this database is not stored in the device itself, but it is available in the form of (single or multiple) text file(s) with the extension .mib. In order to work with the SNMP the MIB database is not necessarily needed, in the SNMP packet there is only the OID, but if we do not know the right OID, then the database can help us find it.

Note: The Promotic driver PmSNMP does not use the MIB database. The MIB can be read by external programs in order to find the addresses (OID) of desired parameters for the PROMOTIC driver.


There is a possibility to configure the monitored side in a way that the agent sends the admin the information (SNMP MESSAGE) automatically without any request. This can happen after a defined condition is met (breakdown, colision, reaching some limit value, ...). This kind of agent configuration is called SNMP TRAP (i.e. trap for events).

Note: Promotic ovladač PmSNMP nepodporuje SNMP TRAP.

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