Traffic measurement should make it possible to obtain the spatial flow of
traffic through the domain, i.e., the paths or trajectories followed by
packets between any ingress and egress point of the domain. A method of
sampling packet trajectories in a packet switching network allows the
direct inference of traffic flows through a measurement domain by
observing the trajectories of a subset of all packets traversing the
network. A method which assumes that the measurement domain does not
change comprises the steps of selecting packets for sampling in accordance
with a sampling function of the packet content and generating a
practically unique label for each sampled packet. The method does not rely
on routing state, its implementation cost is small, and the measurement
reporting traffic is modest and can be controlled precisely. Using the
same hash function will yield the same sample set of packets in the entire
domain, and enables us to reconstruct packet trajectories. An alternate
embodiment which assumes no constraints and that the measurement domain
may change comprises the steps of applying a sampling function and
altering an invariant bit position as a signaling flag in each packet
selected for sampling.
