My WiFi and HomePlug story

[jnitis]

Hiya folks, did a write-up for some friends and thought I'd share it here. Wasn't sure whether to put it in the HomePlug, Asus, Asus N, or Asus AC forum so mods please feel free to move it as you see fit. Cheers.

So my new Asus RT-AC68U finally arrived today and I spent this evening revamping my home setup. Now, I'm a bit nutty with WiFi and home IT projects lately so I also happen to have an Asus RT-AC66U and an Asus RT-N66U as well as my ancient but still trusty Linksys WRT54GL. The story goes something like this.

At some point I bought my first WiFi router which was the aforementioned Linksys. I went for that one because it was cheap, reliable, and known to run many of the interesting aftermarket firmwares. That router was a 1x1 (1 xmit and 1 receive radio path) 2.4Ghz-only b/g router only going up to 54Mbps max. It worked wonders for ages and happily ran my preferred Tomato firmware. Eventually I got sick of the mediocre signal reception in my condos in Asia (which are built with full-on concrete veneered masonry and/or rebarred concrete) and got wind of Asus' new N66 router with 3x3 MIMO (multi-in / multi-out, basically 3 xmit and receive paths simultaneously) being dual band (2.4GHz and 5GHz) and supporting the newer N standard so I snapped that up. The range and speed increases were amazing not to mention all of the funky new things you could do with the latest Tomato builds supported by the much newer hardware (file server, DLNA server, it can fail over to 3G mobile USB sticks if your DSL/cable goes down, and you could basically kit out the firmware to be a full-on server OS so you could install whatever you wanted like BT clients and etc.). Someone even discovered Asus left an SD card slot on the shipping motherboard so I slapped a 32GB stick in there and had transmission (a BT client built to run on a server that you can manage remotely) downloading data and I was super happy. (People also figured out how to plop a USB sound-card into one of the USB slots on the router, load up a streaming audio client, and turn it into a music player that you could connect to your HTS if it happened to be near your router. Imagine your WiFi router doubling as an audio-only Chromecast but this was done years before that came out and was done all with open source Linux based software, so we're talking way cool.)

My current condo provided a lot of challenges to get a reliable signal from one end to the other and that's when I went nuts deep diving into WiFi technical details and was barely able to tweak enough signal to reliably watch YT videos in HD from my master bedroom reliably enough. The other challenge was how to get Internet to my home study. At first I used a 50m network cable but I just got sick of having the eyesore and obstacle to step over a dozen times a day (and the maid would trip over it from time to time) so I got the bright idea to use HomePlug. Fail. The old HP standard was crap and had both crap latency and crap throughput to my study so I then got the bright idea to use a WiFi uplink instead.

I heard about the new AC68 router but it wasn't available in Malaysia yet so I settled for the AC66 which at least supported the new AC standard. I got that puppy up and running and with the latest WiFi driver from Asus (and Broadcom in turn) I was able to easily best the performance of HP with a nice clean 5GHz wireless bridge from my study to my main Internet router. Sub 1ms latency and great throughput.

Throughout all this I lost all my awesome tweaked settings so the reception in my bedroom went down to mediocre and instead of spending time re-tweaking I decided to use the HP devices I had laying around (one end plugged into an electrical outlet near my Internet router and then other in my bedroom) to extend the network to my old Linksys router via my home electrical wiring and again was happy watching YT videos at HD in my bedroom.

Then I heard devices supporting the new HP AV2 standard were available so I gobbled three of those up (one for the main point of entry for my Internet, one for my study, and one for my bedroom) and gave the new standard a try. The good news: latency was totally worked out and is now a consistent 2ms. The bad news: the throughput to my study is still the same at around 37Mbps max which is fine for accessing the Internet but not-quite-fine for streaming BluRay content from my NAS which is physically located in the study to my HTPC in the living room near my main router. With the latency issues resolved I decided to use the new AV2 based HP devices and shut down the WiFi bridge connection as I rarely stream stuff of that high of a bandwidth to my HTPC. And it makes sense to have my NAS in the study on local gigabit Ethernet with my PC since that gets way more use than my HTPC does. (Also, if I want I can probably rig a WiFi uplink directly from my HTPC to the WiFi router directly connected to my NAS in the study that will provide the required bandwidth for BluRay but I'll leave that project for another day. BTW, BluRay needs about 80Mbps for full audio/video, so call it 100Mbps.)

Then I read the AC68 was finally available in Malaysia and I just had to have it. So now I have the AC68 as my main Internet router, the AC66 as my study router, and my first Asus router the N66 as my bedroom router (sadly my ole Linksys has been retired yet again). All three routers are linked with HomePlug. All three routers are 3x3 (3 simultaneous send/receive channels) and dual band (2.4 and 5GHz.). Two of the three support the AC standard, and the one in my bedroom supports N. The newest one supports the new TurboQAM (256 QAM) N-standard enhancement on the 2.4GHz band as well. I've got all three running the latest version of Tomato and broadcasting the exact same SSID on all 6 radios (2 radios per router: 1 2.4Ghz and 1 5GHz). Walking around my condo doing a wireless survey is awesome, all my devices (laptops, phones, and tablets) automatically switch from AP to AP and between 2.4GHz and 5GHz depending on which signal is strongest and offers the most bandwidth.

The whole thing is a hoot but I'm sure my neighbors aren't pleased. With all the RFI if I hang around home long enough maybe I won't need that vasectomy after all..

 

[stevech]

Number of WiFi access devices matters not much, as compared to the WiFi clients that may hog bandwidth streaming video and file downloads 24/7.

 

[azazel1024]

Multiple base stations on a channel though does eat in to available bandwidth. Each one broadcasts an SSID beacon and it'll eat a few percent of available bandwidth.

You can of course shuffle the base stations to different channels, if possible and then that doesn't matter.

That and, it starts taking a really ridiculous number of base stations to really making an impact (you are talking 2-4% per base station). Multiple SSIDs plus multiple base stations is where you start getting in to serious overhead, at least if they are all on the same channel.

3 base stations, with a main and a guest network SSID would be 2-4% x 3 base stations x 2 SSIDs broadcast. So there you can be eating between 12-24% of your bandwidth.

That is part of why having a whole ton of surrounding networks (if at medium to high power) can really hammer your wifi bandwidth even if those networks are dormant. The base station(s) is always broadcasting its beacon. So if you have a dozen really strong networks near you, even if they are only a single base station making up that network, they are chewing up (at least nibbling) your bandwidth with interference with their SSID beacons.

In a situation where other base stations are at rather low receive signal strength compared to the base station you are connected to, the impact is marginal though.

 

[stevech]

Multiple base stations on a channel though does eat in to available bandwidth. Each one broadcasts an SSID beacon and it'll eat a few percent of available bandwidth.

You can of course shuffle the base stations to different channels, if possible and then that doesn't matter.

That and, it starts taking a really ridiculous number of base stations to really making an impact (you are talking 2-4% per base station). Multiple SSIDs plus multiple base stations is where you start getting in to serious overhead, at least if they are all on the same channel.

3 base stations, with a main and a guest network SSID would be 2-4% x 3 base stations x 2 SSIDs broadcast. So there you can be eating between 12-24% of your bandwidth.

That is part of why having a whole ton of surrounding networks (if at medium to high power) can really hammer your wifi bandwidth even if those networks are dormant. The base station(s) is always broadcasting its beacon. So if you have a dozen really strong networks near you, even if they are only a single base station making up that network, they are chewing up (at least nibbling) your bandwidth with interference with their SSID beacons.

In a situation where other base stations are at rather low receive signal strength compared to the base station you are connected to, the impact is marginal though.

What's the time duration of a standard 802.11 (empty payload) beacon transmission as compared to an empty IP packet?

 

[azazel1024]

Beacon size varies depending on which standard you are using, a/b/g or n or ac. The higher protocols use bigger beacon frames as they have to encode more rate information in to the beacon payload.

Basically from everything I have found "size varies". Not including CTS or RTS/CTS, the beacon size seems to vary from around 65 Bytes to ~225 Bytes (for 11n, 11ac is probably bigger). I am unsure if that includes the CRC and header or what. I know that size does NOT include the preamble, which, is 192us for long and 96us for short.

The best I've found is this calculator http://www.revolutionwifi.net/p/ssid-overhead-calculator.html

This guy also has a nice break down of his testing http://wifinigel.blogspot.com/2013/08/its-well-known-rule-of-thumb-when.html

Basically two things you can do, supposing your router/AP supports it, is set higher minimum data rates on the network, as the beacons are sent at the lowest mandatory speed, which is generally 1Mbps, and cut down on the number of SSIDs broadcast.

In effect, at 1Mbps, each SSID and base station consumes ~2.5% of the total bandwidth. At 11Mbps it is 1.05%.

So if you have 2 SSIDs and 3 base stations all within earshot of each other, you'd be burning 15% of your bandwidth if the minimum WLAN speed is 1Mbps, but if you set it to 11Mbps it would be 6.3%.

Its at least in small part why I question router manufacturers that allow you to have a whole slew of SSIDs on a router. I get a primary and a guest, that makes total sense. I don't really see why some let you have, say, 4 primarys and a pair of guest SSIDs. The use cases for that seem tiny and the amount of bandwidth, especially if you don't fiddle with things like WLAN speeds (like, for example, setting g/n as the rates instead of b/g/n, assuming you know you'll never have any 11b clients) and for some reason decide to toss a bunch of SSIDs up...just because, you can be seriously hampering your network speeds just by all of the beaconing going on.

 

[stevech]

Beacon size varies depending on which standard you are using, a/b/g or n or ac. The higher protocols use bigger beacon frames as they have to encode more rate information in to the beacon payload.

Basically from everything I have found "size varies". Not including CTS or RTS/CTS

Aren't beacons broadcast and thus wouldn't use CTS?,

the beacon size seems to vary from around 65 Bytes to ~225 Bytes (for 11n, 11ac is probably bigger). I am unsure if that includes the CRC and header or what. I know that size does NOT include the preamble, which, is 192us for long and 96us for short.

The best I've found is this calculator http://www.revolutionwifi.net/p/ssid-overhead-calculator.html

This guy also has a nice break down of his testing http://wifinigel.blogspot.com/2013/08/its-well-known-rule-of-thumb-when.html

Basically two things you can do, supposing your router/AP supports it, is set higher minimum data rates on the network, as the beacons are sent at the lowest mandatory speed, which is generally 1Mbps, and cut down on the number of SSIDs broadcast.

In effect, at 1Mbps, each SSID and base station consumes ~2.5% of the total bandwidth. At 11Mbps it is 1.05%.

So if you have 2 SSIDs and 3 base stations all within earshot of each other, you'd be burning 15% of your bandwidth if the minimum WLAN speed is 1Mbps, but if you set it to 11Mbps it would be 6.3%.

Its at least in small part why I question router manufacturers that allow you to have a whole slew of SSIDs on a router. I get a primary and a guest, that makes total sense. I don't really see why some let you have, say, 4 primarys and a pair of guest SSIDs. The use cases for that seem tiny and the amount of bandwidth, especially if you don't fiddle with things like WLAN speeds (like, for example, setting g/n as the rates instead of b/g/n, assuming you know you'll never have any 11b clients) and for some reason decide to toss a bunch of SSIDs up...just because, you can be seriously hampering your network speeds just by all of the beaconing going on.

Comparing beacon overhead in 802.11's shared channels should assume a 1 or 2 SSID per AP/router case, as very few consumers even have 2. And the percentage of channel capacity lost to beacons should assume an average client 802.11 bit rate of far more than 11Mbps (802.11b); perhaps 54Mbps average. These make the beacon overhead much smaller and not worth worrying about.

 

[azazel1024]

On your last, if you mean setting your router to higher minimum speeds, yes, that would pretty much aleviate any real overhead.

It isn't based on what clients are connected though, it is based on the minimum advertised speed that the base station will support. If it is set so that 11b clients can connect, in general it'll broadcast the beacon at 1Mbps for most all base stations.

Some base stations you can set to 11g/n compatibility, in which case, I would think, it would only broadcast the beacon at 54Mbps, or maybe 11Mbps. There may be a setting to tweak what speed the beacon is transmitted at, but I have never seen it on a router or access point. The best I have seen is minimum supported standard, which I would assume would change the beacon transmit speed.

My Netgear routers have no option to set 802.11 speed/standards, just the maximum. My TP-Link router only lets me set b only, b/g only, b/g/n or n only. Fortunately I think every single one of my clients is 11n, so I could set that.

 

[stevech]

My post was trying to say that calculating the capacity of the 20MHz channel lost to beacon transmissions, and assuming the channel on average has the low 802.11b speeds, doesn't seem prudent.

It would be like calculating your average gas mileage only while going uphill.

 

[azazel1024]

Dunno, it does to me. Most routers/access points are going to be set with a default of 11b enabled, which means most are going to have a beacon overhead of about 2.5% per SSID/AP. There are certainly going to be exceptions out there, but most consumer gear will be setup that way.

Same on 5GHz, most is going to have 11a enabled, and thus similar beacon overhead.

I think its more ap. to say you should figure it that way, unless you are a hypermiller who has 11b disabled or can set a custom minimum speed on your router/access point so that beacons are transmitted at higher speeds.

 

[stevech]

Horse is dead.