http://www.rfc-editor.org/rfc/rfc5473.txt
RFC 5473: Reducing Redundancy in IP Flow Information Export (IPFIX) and Packet Sampling (PSAMP) Reports, E. Boschi, L. Mark, B. Claise2009-03-01T23:00:00-00:00This method works by separating information common to several Flow Records from information specific to an individual Flow Record. Common Flow information is exported only once in a Data Record defined by an Options Template, while the rest of the specific Flow information is associated with the common information via a unique identifier. This memo provides information for the Internet community.