NCP transmission group trace

An NCP transmission group trace records the activity on all lines contained in a transmission group as if they were a single logical line, including lines in a token ring. The access method and NCP share this trace function. The access method controls, formats, and prints the trace, whereas NCP gathers the information in the trace records. For a detailed explanation of how this trace operates, see NCP and EP Reference, LY43-0029.

Table 1 shows the number of bytes the NCP transmission group trace records for each PIU.

Table 1. Number of bytes recorded for each PIU
Resource	Number of bytes recorded
Middle or last segment PIUs	(TH byte 16 = B'xxxx 0xxx'): (TH + 6 bytes)
PIUs sent to/from a non-SNA device	(TH byte 16 = B'xxx0 xxxx'): (TH + RH + 7 bytes)
Function management data (FMD) unformatted data PIUs	(RH byte 00 = B'x00x 0xxx'): (TH + RH bytes)
FMD formatted data PIUs	(RH byte 00 = B'x00x 1xxx'): (TH + RH + 6 bytes)
All other PIUs	(TH + RH + RU bytes, not to exceed 4096 bytes for any single PIU) See table note.
Note: Because all PIUs that flow over a transmission group are FID4s, the transmission group references are to the FID4 transmission header.

For NCP V5R3 and later, when blocked PIUs are received by NCP, the first PIU in the block is traced. Then the PIUs are unblocked and each of the PIUs are traced individually, which causes the first PIU in the block to be traced twice.