AT&T Labs This memo investigates a scheme to organize registry entries, primarily those defined in RFCs prepared in the IP Performance Metrics (IPPM) Working Group of the IETF. Three aspects make IPPM metric registration difficult: (1) Use of the Type-P notion to allow users to specify their own packet types. (2) Use of Flexible input variables, called Parameters in IPPM definitions, some which determine the quantity measured and others which should not be specified until execution of the measurement. (3) Allowing flexibility in choice of statistics to summarize the results on a stream of measurement packets. Specifically, this memo investigates registry entries that would follow from RFC 3393, the specification IP Packet Delay Variation that allows for many different forms of unique metrics, as a difficult and important test of the registry structure.