RFC3720 10.19. NOP-In NOP-In is either sent by a target as a response to a NOP-Out, as a "ping" to an initiator, or as a means to carry a changed ExpCmdSN and/or MaxCmdSN if another PDU will not be available for a long time (as determined by the target). ... Signed-off-by: Peter Lieven <pl@kamp.de>