Thank you all for the quick response. Unfortunately I'm still having some trouble. This is what I have so far ( Its a lil messy but just for testing it should work ) This is based on the Client implementation: http://cgit.osmocom.org/gr-osmosdr/tree/lib/rtl_tcp/rtl_tcp_source_f.cc#n275 #define COMM_SET_FREQ ((unsigned char) 0x01) struct command{ unsigned char cmd; unsigned int param; }; unsigned char cmds; int iFreq = 500000000; cmds = COMM_SET_FREQ; struct command cmd = {cmds, htonl(iFreq)}; answer = send(sConnect, (const char*)&cmd, sizeof(cmd), 0); and the response is : client accepted! set freq -858993635 ll+, now 1 ll+, now 2 ll+, now 3 I'm sure I'm missing something I just don't know what. Thanks