Streaming through WLAN doesn't exceed 1.2MB/s

Question

Transfering files is slow even after I disabled RDC compression and Windows 7 autotuning. Link speed is 54Mb/s.

Answer 1

That's about all you can expect from 802.11g (or 802.11a) under real-world conditions. Especially if both the source and destination of your stream are wireless devices.

First, sometimes Wi-Fi link speeds are listed by their max possible PHY rate, but the actual PHY rate you can maintain at your distance may be somewhat lower. So instead of the full 54 megabit/sec rate, you may have stepped down to one of the lower rates in the standard: 48, 36, 24, 18, 12, 11, 6, 5.5, 2, 1.

Even if you're truly maintaining the 54 megabits/sec PHY rate, Wi-Fi is half-duplex and less efficient than wired Ethernet. On 802.11g or 802.11a, the rule of thumb is that your TCP-over-IPv4 throughput will be about half of your PHY rate. 802.11n and 802.11ac do "frame aggregation" to improve efficiency, but even those only get to 70% or barely 80% efficiency.

So, 54 megabits/sec * 0.5 (50%) efficiency = 27 megabits/sec = about 3.2 MebiBytes/sec. So even if you're truly maintaining the 54 Megabits/sec PHY rate in the direction that matters, you're not that far off from the best throughput you could expect.

If your stream is wireless-to-wireless through the same AP, then you can cut your expected bandwidth in half again, because every packet takes up airtime on the channel twice: once from the source to the AP, then again from the AP to the destination. So 1.6 MebiBytes/sec is the best you could expect.

If your stream is wireless to one AP, via a wireless WDS (relay, extender) link on the same channel, to another AP on the same channel, then to a wireless destination, then your traffic crosses the air three times, so your best expected throughput would be less than 1.1 MebiBytes/sec.

And this has all been assuming you're on a completely clean channel and with nothing else going on except this one stream. If anything else going on on your devices is using the network, or if you have other devices using the network, then they're taking up a slice of your airtime. So even though you may be getting the 54 megabits/sec PHY rate whenever you send or receive a packet, you might only be getting half of the available airtime.

If I may editorialize for a moment: Overall, you're overdue for ditching 802.11g. It's been over a decade since that stuff was state of the art. Back in 2002 or 2003, people were happy to get 1-3 MebiBytes/sec of file transfer throughput. But you're right that by 2014 standards, that's painfully slow. Moore's Law stops for no man. Make the leap to 802.11ac. Since you seem like the kind of person that keeps networking equipment for a long time, make sure you jump to the fastest flavor of 802.11ac, which is currently 1300 megabits/sec. Look for a dual-band concurrent AP that also does 450 megabit/sec or better 802.11n in the 2.4GHz band. Many vendors add up the max 5GHz (802.11ac) rate plus the max 2.4GHz (802.11n) rate, and then call it "AC1750". Also remember that to get the new speeds, you'll need to upgrade your wireless client devices as well.