On Wed, Jan 14, 2015 at 08:24:02PM +0000, Christian Weisgerber wrote: > On 2015-01-14, Stefan Sperling <s...@stsp.name> wrote: > > > 15Mbit/s sounds as if it maxes out at 18Mbit/s (the highest QPSK rate) > > and never switches to OFDM rates (24 - 54 Mbit/s). > > IEEE 802.11 still uses a shared medium and CSMA/CA, right? (Wikipedia > says so.) So the transfer between two nodes is effectively > half-duplex. The overhead from switching the transmission direction > back and forth will alone reduce your throughput substantially. > Leaving TCP ACKs aside, the 802.11 layer 2 protocol also acks data > frames, so even strictly unidirectional data transfers on a higher > layer will suffer from underlying carrier turnaround.
That's right. Also, labels like "54Mbit/s" apply to the transmission rate of the data part of a frame. There is still a preamble and header which is always transmitted at 1Mbit/s for legacy compat. Not all bits fly at the same speed in wifi.
