RPI as Related to Scan Time

I have a CompactLogix and some Remote I/O, which I am communicating to using implicit messaging over EtherNet/IP. I'm curious as to the relationship between scan time and Requested Packet Interval (RPI). In setting up my implicit messaging to the remote I/O I'm promted to put in an RPI, which I do (arbitrarily picked 200 ms). My question: I come from a Modicon background, and with Modicon PLCs you don't set an RPI. Bascially, remote I/O is serviced at the end of PLC scan. In Allen-Bradley, which "prevails"...RPI or the scan time? i.e. if my scan time is slower than the RPI or faster for that matter), then what happens? Arun