802.11g - 54 Mbit/s
802.11n - up to 600 Mbit/s depending on your hardware
However, for most people, whose 802.11n will run in the 2.4 Ghz band, you'll only get over 54 Mbit/s if you have no 802.11g or other 2.4Ghz ISM devices anywhere near your setup, and that's unlikely. If any of your devices are 802.11g then you are likely to be running at 802.11g speeds i.e. 54 Mbit/s. If you run your 802.11n at 5GHz your chances of getting a higher line rate improve dramatically, but this usually requires two things:
- a wireless router with two radio access points, one for 5Ghz and one for 2.4Ghz. Only the expensive ones have this feature.
- 802.11n client devices that work in the 5Ghz band, and these are rare, because the standard doesn't require this mode of operation.
Bottom line: you're far more likely to be running at 802.11g line rates of 54 Mbit/s, regardless of what your router is rated for.
It gets worse. From the 54 Mbit/s you have to deduct the overhead for the contention process, interframe spacing, PHY level headers (Preamble + PLCP) and acknowledgment frames. You also get the problem that wireless is half duplex, so can only transmit in one direction at a time, so as well as the PHY acknowledgement frames you also get higher layer protocol acknowledgement. The rule of thumb for this is that the overhead will take 10% of the bandwidth, and the higher layer protocol acknowledgement will potentially halve the throughput depending on the protocol - so now you're down to 25 Mbit/s. Factor in the bits to bytes conversion (divide by 8), remove another ~10% for higher layer protocol overhead (packet headers etc.) and you have ~3Mbytes/sec of real data.
That 3 Mbytes/sec is shared between all devices on your wireless. Oh, and any interference from neighbours wireless LANs, cordless telephones, microwave ovens, video senders etc. will reduce the throughput even further. Hence, as Aldanga says, you end up in the 1-3 Mbytes/sec range, but typically nearer the bottom end, unless you have specifically designed your system and selected your components to operate over 802.11n in the 5Ghz band.
This post has been edited by Heimdall: Sep 5 2010, 09:44 AM