Which are considered to be the oldest suttas?

Though I've seen dating of mahayana suttas here and there in passing with some analysis, I understand the pali canon has suttas of many ages. For example, one collection I've often heard to contain many old suttas is the *Itivuttaka*. However, I've don't recall seeing any information about dating of specific suttas, or what criteria for estimating the age are used. Is there a set of suttas which has been identified as the possibly oldest texts?