IS-IS and OSPF are both link state. They both use SPF, but after SFP runs on IS-IS it then uses PRC making it just a bit faster/efficent than OSPF. If PRC is better why was it never integrated into OSPF? Afterall, OSPF is more widely used, and one would think OSPF would utilize every advanced feature that allows speed, and scalability. Hopefully this didn't seem like an uneducated question.