+ length - length of buffer to read or write,
+ (default 128 KB for TCP, 8 KB for UDP)
+ type: int
+ unit: k
+ default: -
+ window - set window size / socket buffer size
+ set TCP windows size. for UDP way to test, this will set to accept UDP
+ packet buffer size, limit the max size of acceptable data packet.
+ type: int
+ unit: k
+ default: -