Proposed enhancements to the XDR UDP metric packets

High-level requirements and possibilities

include a source UUID representing the source host
security
- include an authentication digest similar to the 4 byte signature on SRTP packets
- encryption of the packets
network efficiency
- combine multiple metric values into a single UDP packet up to the permitted MTU
metric namespace
- support for arrays of metrics (e.g. cpu[0], cpu[1])
- support for metric hierarchy/tree structure
- possible use of a UUID instead of a metric name for each metric
timestamp
- include the timestamp when the metric was sampled (which may be earlier than the moment it was transmitted on the wire)

backwards compatibility:
- new version of gmond should be able to receive packets from the current version as well as receiving the new format
- it should be possible to represent the data in the same XML schema (so that gmetad and other in-house scripts for parsing the XML will still work)
- it may be possible to offer an enhanced XML schema to support the new features, and a config file option should exist in gmond.conf to select new or old XML output format
not all features will be implemented immediately
- e.g. the packet format may reserve space for an authentication digest, but gmond might not have any code for generating such a value until further in the future