This reports which direction of traffic on this source port is being mirrored into the monitoring session -- receive, transmit, or both. Mirroring only transmit traffic instead of both directions halves the volume of copied packets a capture appliance has to handle, so this field is a deliberate choice an admin makes based on which side of the conversation actually needs to be analyzed on Fi-A/1/5. A value of 'both' here means every packet in or out of Fi-A/1/5 gets duplicated to span-1's destination; a value of 'rx' would mirror only inbound traffic.