Hello Mikeatbosch
You can find information about it, here, at the NI-XNET Hardware and Software manual on page 4-15.
You can also find examples if you go to the example finder: open LabVIEW>>help>>find examples>>Hardware Input and Output>>CAN>>NI-XNET>>Intro to Sessions>>Frame Sessions>>CAN Frame Input Queued.vi
Regards
Frank R.