gtps2m3yACF/SNA Data Communications Reference

Appendix D. Using the Path Information Unit (PIU) Trace Facility

The path information unit (PIU) trace facility provides a detailed trace of the data transferred between the TPF system and remote resources. Each time the TPF system sends or receives data, some, all, or none of that data is stored in an entry in the PIU trace table depending on the resources that you are tracing. Later, you can display the entries in the PIU trace table online, or write the PIU trace table to a real-time tape and create a PIU print (PIUPRT) report to view or print offline.

The data stored in a PIU trace table entry can be a PIU in FID2 or FID4 format, a network layer packet (NLP), or an 8-byte channel-to-channel (CTC) header (which is included in all read and write channel programs during normal CTC data transfer operations). You can trace the data for all of the resources in the network or for only specific resources in the network. You can also trace only particular types of data, such as data for high-performance routing (HPR) traffic or data for network control (NC) commands and virtual route (VR) pacing requests and responses.