Template parameter TP_OUTPUT_PORTS will also determine the number of the pktmerge graph constructs used by the pkt_switch_graph class.
The pktmerge takes a number of input packet streams and merges them into a single output packet stream.
See UG1079 Packet Split and Merge Connections for more details.
Number of streams each pktmerge element merges is determined by the below formula:
N_STREAMS_MERGES_TO_PKT = TP_SSR / TP_OUTPUT_PORTS