This article applies to PRTG Network Monitor 19 or later

The Meaning of the SNMP RMON Sensor’s Transmitted Channel

The SNMP RMON sensor monitors the traffic on an SNMP-compatible device and can show traffic data for each available port. For this purpose, the sensor uses the RMON MIB. Unfortunately, the RFC for this MIB does not exactly describe what is counted in etherStatsOctets (that is, the counter that is used for the Transmitted channel). For a description of the SNMP object etherStatsOctets, refer to Cisco’s SNMP Object Navigator.

Because the description refers to network and not to interface, we usually interpret transmitted as total traffic on the device. This corresponds to the sum of the Traffic in plus Traffic out channels of an SNMP Traffic sensor. Random tests on some HP switches in our labs confirm this assumption, as well as occasional feedback from our customers (for example, for the 3Com Superstack switches 3200, 3300, and 4400).

Apart from that, some manufacturers might interpret etherStatsOctets differently. Considering feedback from PRTG users, switches from D-Link (for example, DES-3200, DGS-3100, DGS-3120, DGS-3240, and DWS-4026) only count octets that go into an interface (Traffic in); the same goes for some Allied Telesyn switches (for example, the AT-3850GB).

Finally, the value that is shown in the Transmitted channel of the SNMP RMON sensor highly depends on the interpretation of your switch’s manufacturer. If the producer of your device does not interpret this counter as traffic total, you can manually rename the Transmitted channel to, for example, Received, depending on what is actually counted.