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Wireless speed question

Smallclone

Well-known Member
Hello.

I have a nice fast wired connection on my pc (100MB). It's Virgin Media, in modem mode with an Asus RT-n66u router. But when I test the speed wirelessly, it is only around 25- 30MB. Happens on smartphone, laptop and tablet - even right next to the router.

I have tried changing channels, and changing from 20Mhz to 40Mhz but it's always the same.

One thing I have noticed is that on my smartphone, using the "wifi-analyzer" app - it always says I am on channel 6 - even though I change it to channel 1 etc

Advice appreciated
 

mickevh

Distinguished Member
First, be sure you know your bits from your bytes: Network link rates are usually reported in "bits" (small "b") whereas a lot of other computing quantities are reported in "bytes" (capital "B.")

Next be sure to understand that network "speeds" are a report of "rate" not "quantity." Like the speedometer in a car - the value indicated does not tell you how many miles you are traveling ("quantity" of miles - distance travelled,) it tells you your rate of progress. In an urban car journeys you are required to stop and start at junctions, traffic, etc. In data networks, the protocol rules mandate "pauses" in transmission, there's competition for the transmission medium, traffic, error correction overheads to name just a few, which affect the throughput of user data. However all the bits in flight proceed at the reported rates. Just don't fall into the trap of thinking "speed" means "quantity" ("distance" if you like in the car analogy,) "speed" means "rate."

Wi-fi link rates are a function of both the client device and the router. A lot of client devices, esp. things like phones and tablets are much less capable than a good router, less antennas for example, which affects max. link rates. You need to check your client device specs and see what they are capable of.

Getting 40MHz channels (which similarly affects link rates) is getting tough in the 2.4GHz waveband if you have neighbours as there are "rules" in the protocols about "playing nice together" which can prevent 40MHz transmissions.

And some protocols are simply slower than others. "A" and "G" standards max out at 54mbps which gives a user level throughput (in good conditions) of about 25-30mbps. If your client devices are "only" A/G capable then the throughput you observe is in about the right ball park. Again, check the specs. and see what they are capable of.

You set you wi-fi channel on your router/AP and the clients all tune in to it. There is another form of wi-fi called "ad-hoc" mode whereby wi-fi devices talk to each other directly without using a router/AP. If you are looking at channel setting on client devices, it's a setting only applicable to this "ad-hoc" mode. If you are using "infrastructure" mode wi-fi (ie wi-fi with a router/AP) then such client channel settings is irrelevant. The only place you set your wi-fi channel is in your router/AP.

Unfortunately, it is all rather complicated. :D
 
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Smallclone

Well-known Member
Thanks for that. I have been using the router dashboard to change the channel. I know the devices can pick up speeds of at least 60Mbps because I've seen them do it before.

Do you suggest changing from 20/40 Mhz to simply 20Mhz ?
 

Prem

Standard Member
RT-N66U is a dual band router which supports both 2.4 GHz and 5 GHz bands. 2.4GHz channel gives better range, but is prone to interference from other wireless devices. Try using the 5GHz channel and check if you get better throughout (it might as you said all your devices are close to the router)
 

mickevh

Distinguished Member
20/40MHz, just don't be disappointed if you have neighbours and it doesn't work 40Hz. There's no chance in the flats where I live, I only ever get 20MHz transmissions. To get 40MHz channels I have to use the 5GHz waveband which no-one else is using (yet.)

There's an FAQ in this forum about "wi-fi interference" which discuses how to survey your locale and choose the optimum channel. You might like to take a look at that and see if you can find a better channel.

Be aware that some client devices (and some routers, but not yours,) don't support 5GHz operation.
 

Smallclone

Well-known Member
Yeah the 5GHz works if you have direct sight to the router. But not really much use for the house.

It's not that the speed is unusable. It works ok, I was just very surprised at the difference between wired and wireless.

I don't suppose that my old router downstairs acting as an access point is causing this?
 

mickevh

Distinguished Member
Yeah the 5GHz works if you have direct sight to the router. But not really much use for the house.

Yep - 5GHz doesn't penetrate "stuff" (walls, doors, air,) as well as 2.4GHz. It's a fact of physics.

I don't suppose that my old router downstairs acting as an access point is causing this?

Could be. And not just the router, also all the clients associated with it. Wi-fi doesn't work by creating some kind of "energy field" (called "wi-fi signal") that surrounds a router/AP like a TV transmitter - that's the wrong model to have in your head. Wi-fi works like walkie-talkies - everything transmits and there's a "transmission footprint" surrounding every wi-fi device when it's transmitting. Any nearby transmitters can interfere with each other (routers, AP, clients and anything else) though the protocols are designed to try and minimise this so everything plays nice together.

If you have multiple AP's you need to ensure they are tuned to different radio channels that are at least "5 apart" if you are using 20MHz channels (say 1, 6, 11.) However, there's not enough frequency spectrum available to create multiple 40MHz channels. So you could create one 20MHz and one 40MHz (say C1 @ 20Mhz and C6+9 @ 40MHz) or do what we do in big installations with multiple APs's and constrain them all to 20MHz channels in the 2.4GHz band. EDIT (and accept that that means the link rates will be lower, but interference will be reduced, possible eliminated.)

In the 5GHz band, there's much more frequency spectrum so you can form more non-overlapping channels, (36+40 @ 40MHz, C44+40 @ 40MHz etc.)

With the new AC standard it gets even more complex as that permits 80MHz and 160MHz channels. Fun times ahead.
 
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Smallclone

Well-known Member
If you have multiple AP's you need to ensure they are tuned to different radio channels that are at least "5 apart" if you are using 20MHz channels (say 1, 6, 11.) However, there's not enough frequency spectrum available to create multiple 40MHz channels. So you could create one 20MHz and one 40MHz (say C1 @ 20Mhz and C6+9 @ 40MHz) or do what we do in big installations with multiple APs's and constrain them all to 20MHz channels in the 2.4GHz band.

I think this is a good starting point. I'll configure the AP and try some permutations. Thanks.
 

mickevh

Distinguished Member
Forgot to mention that ethernet and wi-fi performance can't be directly compared on a like-for-like basis. Because the wi-fi protocols and operating paradigms incur a lot more "protocol overhead" (as it's known) one expects lower application level throughput using wi-fi than ethernet.

By way of example, using as I type, using 300mbps wi-fi in close to "ideal" conditions (LOS between laptop & AP @ < 5 meters, only 1 client, no interference from the neighbours, 5GHz, 40MHz channels,) I see throughput of the order of 150mbps - 180mbps at the application level. If I had more contention for air time (more clients,) interference, intervening structure, greater distance, etc. one would expect that to get worse.

Compare with a fast ethernet link (100mbps ethernet was called "fast" when it was introduced way back when) in a switched ethernet infrastructure where I get or the order of 80-90mbps at the application level. Ethernet is much more efficient.
 
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