Calculating Delta Values from SNMP Counters

I am looking to create gauges from the counters I am receiving via SNMP polling. The network equipment I'm monitoring simply counts packets received and transferred using a counter, yet doesn't provide any data regarding the rate over time.

I am attempting to poll these devices on a fixed interval, thus allowing me to create a delta function in order to extrapolate BPS per network device.

Is there a plugin for Elasticsearch or Logstash that will do this for me? I've tried using the 'metrics' plugin to logstash but that doesn't seem to work, nor do I understand how to isolate the metrics per device. I've also looked into metric aggregations, which is likely the way I'll end up going if no simpler solution is available. However metric aggregations seem a bit heavyweight for this simple task.

If metric aggregations are the easiest method of implementing this monitoring solution, are there any good examples out there for someone that's relatively new to ELK and doesn't know much about JSON? Thanks in advance.

Installed: 1:2.2.4-1
elasticsearch: 2.3.1
The switches are Mellanox Infiniband switches, SNMP polling their transfer rate gauges brings back generic numbers which signify they haven't enabled the gauges.