What is the bandwidth usage by Spectrum when polling a device?
For example: "What is the bandwidth utilization when polling a Cisco 2841 router and all its managed ports."
Bandwidth utilization very much depends on the type and size of the device being polled.
This means polling a huge router will deliver much more information than for example a server.
Running the Spectrum sizing wizard (available through pre-sales or support) gives you the approximate network usage in relation to polling many 100's of devices.
The results will provide details in Mbits/sec of SNMP traffic from polling and logging.
Calculating the bandwidth usage of a single device is very difficult to do however it would be nearly negligible with only a small number of packets being sent back and forth.
When polling 2000 devices (1000 servers and 1000 networking devices of various types) the bandwidth is only around 3 to 4% utilization with an occasional spike of 6%. This being based on a 100 BaseT line.
However as stated it should always be considered that calculations are always dependent on the device type and what you are asking Spectrum to poll for.
Also note that POLLING functions differently from MODELING. Spectrum will use a little more bandwidth when it is modeling a device (though not significantly more).
Even on an ISDN link a 2841 router should not use more than a few packets to poll and as such any utilization seen would be minimal for one device of that type.