Investigation showed that DCMTK unfortunately always set TCP send and receive buffers by setsoc
bufLen = 65536; // a socket buffer size of 64K gives best throughput for image transmission
setsockopt(sock, SOL_SOCKET, SO_SNDBUF, (char *) &bufLen, sizeof(bufLen)); (void) setsockopt(sock, SOL_SOCKET, SO_RCVBUF, (char *) &bufLen, sizeof(bufLen));
This was probably good approach before TCP autotuning was introduced, but since it is available in newer kernels (>2.6) setting SO_SNDBUF or SO_RCVBUF is switching off the TCP autotune feature that results terrible performance over 10 Gb/s (see https://www.psc.edu/index.php/networking/641-tcp-tune)
When I commented out these setsockopt lines in
the newly built tools could reach ~5.2 Gb/s bandwidth utilization.