Trends in Technology: The Details of SNMP


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Of course there are plenty of other devices that support SNMP and will act as agents. After you obtain an SNMP manager you will then need to configure it with the agent's address and its appropriate MIB. Let's review the necessary steps again:
Obtain an SNMP manager (can be software or a device like Relio)
See whether or not the device you want to monitor supports SNMP (if not, stop right here)
Obtain the MIB of the device you want to monitor
Determine the write community and read community names. These are like rudimentary passwords. The manager will use these as it accesses the agent.

You'll need another piece of software now known as a MIB browser. The MIB browser reads the MIB, and after connecting to the device you want to monitor, reads the real-time data that is available, and tells you the OID that corresponds to pieces of information that you want. We use a freeware MIB browser from iReasoning that you can download at ireasoning.com/mibbrowser.shtml.

Figure 5

Figure 5.


I've used our microwave receiver at Times Square as an example. See Figure 5. I obtained this entire graphic by telling the MIB browser to perform what is known as a WALK command (which it does by sending get-next-request messages to the agent). What you see is a huge collection of information -- way more than you'll ever need to use. (If you look at the left window, you'll see the MIB opened with the tree icon at the top, and leaf icons all the way at the end of the branches. Leaves correspond to the actual data being read.) Experience has shown that it is much easier to use a GUI or Web browser to determine just what you really want to monitor later via SNMP. (Ask yourself which variables are the most important while you study a device in real-time by way of its GUI or a Web browser). Other times the descriptions of the OIDs are easier to figure out. In the example you can see that I've highlighted receive level and when I do so, the actual OID for that leaf is shown at the top/center of the picture. Copy and paste that OID in to the appropriate spot in your SNMP manager, so that it knows where to look for the data you want it to read. Configure your manager to read the data and let you know if something happens to it (like it goes to zero, for instance).

I've barely scratched the surface on what can be done via SNMP. This is the sort of thing you can teach yourself on a rainy day. It's nothing new -- our IT colleagues have been using it for years - but since network connectivity is still a relatively new feature at many remote broadcast sites, protocols designed for use over networks are just now making their way in to our technical vernacular.


Irwin is transmission systems supervisor for Clear Channel NYC and chief engineer of WKTU, New York. Contact him at doug@dougirwin.net.




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