difxfilterbank is a simple program designed to catch UDP multicast messages from DiFX which contain autocorrelations. It is really just a test program, used to obtain data for offline processing. Ultimately, the searching described below will be integrated into an online, realtime program.
The autocorrelations contained in the binary messages which difxfilterbank catches are produced by DiFX if it receives a certain control message telling it to start producing dump data. The autocorrelations come the short-term accumulations (STAs) held at the Core nodes in DiFX. This allows quite good time resolution to be obtained - tens of ms in DiFX1.5, and sub-ms in DiFX2.0 (see this link for an explanation of the difference).
The reason for squirting these STA values to an external program to DiFX is for the purposes of transient searching. The STAs are buffered and searched for single pulses of varying duration and dispersion.