Hello Carl,
your understanding is correct.
IPFIX is defined in RFC 5101 of January 2008
http://www.ietf.org/rfc/rfc5101.txt
and it is thought to be used for the same purposes as Netflow.
The network device will export flow based statistics data to a Collector.
the flow is defined based on the following:
A Flow is defined as a set of IP packets passing an Observation
Point in the network during a certain time interval. All packets
belonging to a particular Flow have a set of common properties.
Each property is defined as the result of applying a function to
the values of:
1. one or more packet header fields (e.g., destination IP
address), transport header fields (e.g., destination port
number), or application header fields (e.g., RTP header
fields [RFC3550]).
2. one or more characteristics of the packet itself (e.g.,
number of MPLS labels, etc...).
3. one or more of fields derived from packet treatment (e.g.,
next hop IP address, the output interface, etc...).
A packet is defined as belonging to a Flow if it completely
satisfies all the defined properties of the Flow.
Hope to help
Giuseppe