SNMP I/O Addressing
Object IDentifier. A part of the SNMP driver addressing system. values. The VTScada SNMP Address Select tool (Address Assist / Address Select) will help you build addresses for your I/O tags.
Before using the Address Select tool, you must first tell VTScada where to find the MIB Management Information Base. A hierarchy of the information available to an SNMP device, organized by numbered Object Identifiers (OIDs). file for your device. You will need to obtain a .MIB file from your equipment manufacturer. (If the user knows the OID there is no need for a MIB.)
It is possible to create a VTScada SNMP Agent service, to serve tag values over SNMP. But note that table addressing and reading tables is complex. As one example, the OID for a table entry contains the content of the entry and is not fixed. Therefore, for VTScada I/O the user must obtain the table entry using a third party SNMP software program, obtain the full OID, and then use it in VTScada IO address. While GetBulk and GetNext are useful in walking a table, VTScada I/Os do not use these functions (although they are implemented in the driver). The user must write a script to call these functions and pass their values to I/O tags.
SNMP data types influence your selection of I/O tag:
SNMP supports 12 data types. These are passed directly to the I/O tag, where further processing may be required.
- SNMP data types: Integer32, Unsigned32, Gauge32, Counter32, Counter64 and TimeTicks can be used with numeric tag types.
- SNMP data types: Integer(Enumerated), Octet String, Object Identifier, IpAddress, Opaque and Bits should be read in with a StringIO tag, with additional processing done using a Calculation tag as required.
SNMP Address Configuration
There are two parts to address configuration. The first is to obtain the required .MIB file(s) and import them into your application. The second is to build the address using the built-in SNMP Address Select dialog (shown later in this topic).
Importing a .MIB
- Obtain a .MIB file from your equipment manufacturer.
- Save this file to a folder on your VTScada server computer.
All .MIB files that will be used by an application will be stored a folder named "MIB" within your application directory. You can create this folder yourself and copy the files to it. If using the Import MIB button, VTScada will create the folder and copy the selected files to it.
- Import the file into the application's version control system.
There are two ways to do this:
- Click on the application's Import File Changes button in the VAM.
Or:
- Create and configure an SNMP driver tag in your application.
- Select that driver in an I/O tag, such as an Analog Input.
The address field of the I/O tag will now have a MIB button. - Click the MIB button - the SNMP Address Select dialog will open.
- Click the Import MIB… button.
- Select the file.
If the .MIB file depends on other .MIB or .MY files, you will get an error message in the Address Select tool (step d. above). Hovering over the error will open a tool-tip window, display the name of the missing file. Locate and copy this file to the MIB folder, then use the Import File Changes button in the VAM.
Building an address.
The following instructions assume that you are configuring an I/O tag that uses an SNMP driver and have reached the stage of building the address.
A MIB button can be found beside the address field when an SNMP driver has been selected as the I/O Device.
- Click on the MIB button.
- Navigate through the tree to select the device you wish to address.
Note that you can hover over a node to see extra information.
- If required, enter the Table Index number, specifying the row in the SNMP table.
The Table Index is the last number in the SNMP address string.
- Click OK.
The Disable Polling option will turn off regular polls for this OID. Use this when you want to receive data from traps only. Adding the :NS (no scan) suffix after the SNMP OID will cause the same result.
The result will be similar to that shown here:
