The tx and rx will be automatically added when you create a link from that device and choose the port to graph the bandwidth with. As shown below…
If you wanted to add the tx/rx to a label you can use the following oids.
1.3.6.1.2.1.2.2.1.10 will list the rx amounts on the device’s ports.
1.3.6.1.2.1.2.2.1.16 will list the tx amounts on the device’s ports.
I put the OID on the device label, without the need to create a link, as in the example attached.
In the example, I’m putting the “TX EX” purposely wrong, to be printed in the OID screenshot.
The OID proposal, is the Total Octets sent, but the link or else using another oid is some function to convert the octets and not being a total traffeged ..