From Wireshark capture, it looks like DSP sent the echo packets back but didn't get the response from PC within time, so the packets re-transmitted via TCP, the PC received duplicates. The echoc.exe is not the way to benchmark DSP throughput, however you can use the HUA demo under mcsdk_2_01_02_06\demos\hua for TCP and UDP TX/RX throughtput purpose.
Regards, Eric