Hi all, The airtime_link_metric_get() function follows closely section 13.9 of the standard, except for the "channel access overhead" which is said to depend on the PHY, headers, etc. Hence I understand that a complete implementation is not trivial. The 'device_constant' variable is given the constant value '1<<ARITH_SHIFT', which means 1 microsecond if I am correct. But the smallest possible duration for the PPDU header is 20 microseconds in non-HT or 24 us in HT, as shown in section 20.3.2 For the test frame of 8192 bits, say at 300Mbps (MCS15), Bt/r = the currently computed airtime is 28 instead of 51, underevaluated by -45% ! Since the value accumulates on the mesh path, it may make a big difference for the path selection. Questions: Even if device_constant is kept as a constant, shouldn't we set it to something more realistic, like 20 or 24 ? (I mean 20<<ARITH_SHIFT) Does the standard really mean to include the PPDU header ? (By the way, I understand that this value should also include the DIFS, and maybe the ACK, so it should be much greater than 20) Regards, Jean-Pierre Tosoni -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
