Wi-Fi 802.11ac 1.7 Gbps (160MHz channels) advisory

Discussion in 'Networking and Wireless' started by downloads, May 1, 2018.

  1. downloads

    downloads Super Moderator Super Moderator

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    Hello and welcome to a thread dedicated to 802.11ac Wi-Fi and specifically to questions and issues related to 160 MHz channels.
    802.11ac standard has been with us for a while now and so were - in theory - 160 MHz channels, however there were no Wi-Fi cards capable of 160Mhz channels until Intel 9260 came along, so that part is new.

    As such people are not aware of specific issues that arise only or mostly when those channels are used.

    Let's get through some of the basics:

    1. How 160 MHz channels came to be?

    These channels are either two continuous 80MHz channels bonded together (usually designated as 160) or two separate (not continuous) 80 MHz channels working together (usually designated as 80+80).

    The second type - 80+80 is far better for a couple of reasons - one is that it's hard to find a clear/free 160MHz of 5GHz band but it's much easier to find free 80MHz, so one could use two free channels to form one super-channel
    Secondly one could use two non-DFS channels to form 160MHz channel i.e. one from the lower part of spectrum (channels 36-48) and one from the upper part (149-165) omitting the middle part where DFS is required.

    This all sounds great but not all of the routers support 80+80 and moreover we are not sure that Intel 9260 and its twin Killer 1550 even support that.

    2. What the hell is DFS?

    DFS is Dynamic Frequency Selection - it's goal is to stop routers and other 5GHz devices interfering with weather radars (see this file if you're interested in details - PDF).

    The idea is that the router will detect specific radar patterns and will switch channels to avoid causing interference.
    Also once the router is booted up, before the 5 GHz radio starts it's going to scan the channel to make sure it can be used without causing interference to any radar installations.

    On most channels that scan takes 1 minute and in that time it might seem like 5GHz radio is not working, but on some channels it takes 30 minutes (I don't have a source for that but it seems on upper channels)
    See this for details.

    Oh and the channel the radar got detected on gets blacklisted for 30 minutes. o_O

    3. On what channels is DFS required?

    That depends on where you live - as usually rules are different all around the world.
    In the US DFS requirement starts from channel 52 (lower boundary is 5250 MHz) and goes all the way to and including channel 144 (upper boundary 5730 MHz).

    As a result in the US non-DFS frequencies are 5170 MHz to 5250 MHz (that's 80MHz wide) and 5735 MHz to 5835MHz (100MHz wide).

    As you see there is no way to for a continuous 160MHz channel on any of non-DFS frequencies.


    4. What's wrong with DFS?

    Almost everything, really. What happens is that once the router discovers what it thinks is a radar (based on the characteristics hard coded in the driver for your wireless chipset that are supposed to recognize radar patterns) your device has 10 seconds to vacate the premises.

    It does so in an elegant and sophisticated manner - by dumping any and all connected devices and switching to another channel. And I mean that literally - it disassociates all wireless client immediately regardless of whether any data is transmitted. Also there is no roaming here, so clients do not get moved to another frequency/channel.

    Before the router can establish new network on a new channel it has to scan it - which as mentioned above takes no less than a minute.

    As a result your wireless connection might get dropped at any minute stopping any transmission and possibly damaging data and then there will be no SSID to connect for another minute.

    Mind you once the wireless connection is reestablished you're not out of the woods yet. Any backups you might have had going are down at this point, any secure connections that require authentication will requite re-authentication (often manual) and anything you've been doing - streaming, downloading, VoIP is down at this point.

    5. I don't live near the airport so radars are not a problem for me. Why should I care?

    First of all what is near? According to this source "near" is defined in DFS documentation as anything within 35km (21 miles) of a radar installation. That does not really sound like "near", does it?

    If you live in a city your chances of being within 21 miles of an airport are rather large - welcome to DFS zone :cool:

    Secondly I very much doubt this patterns are correctly recognized. My router drops 160 MHz connection on multiple 5GHz channels roughly twice a day. Does it sound plausible that the weather radar would be switched on twice a day? Are the electricity bills that high?

    I seriously doubt that whatever my router discovers is a radar. While I do live within 21 miles of an airport I do live in a large city and I do not live in a skyscraper. Basically I live on a low floor of a building some 8/9 miles from the airport and between me and the airport there are lots of tall buildings and skyscrapers.

    As such I suspect my router is not picking up any radars - more like something on 5GHz operated by one of my neighbors.

    6. Why not disable DFS, than?

    This can't be done - it's built in the driver and as such if it's deployed by the manufacturer of the wireless chip, it can't be disabled.
    What's more if you've managed to disable scanning somehow, you wouldn't be able to connect to any 5GHz networks anyway because DFS scan has to be complete before SSID can be created. Remember that 1 minute wait I mentioned before - that's when the scan takes place and unless it's finished SSID won't be created.

    I tested that on a router that has a separate radio which seems to be only used for scanning. It seems not to have been enabled before the latest firmware, but with the latest firmware it seems to be on and once I disconnected antenna from it 5GHz radio never got enabled. To clarify 5GHz radio was a separate radio that still had its antenna connected at the time.

    7. But speeds are great with 160MHz channels. 100MB/s over Wi-Fi!

    That is true - it looks nice and all. On a free channel in the DFS zone I managed 96MB/s download over ftp from NAS.
    Not that the connection was able to stay reliably on for 24 hours...

    What would you rather have - a slower connection that's reliable or a flakey one that's insanely fast?

    8. My router does not disconnect like that!

    Maybe it doesn't - maybe you live far from radars and there is no interference that your router picks up and wrongly recognizes as radar interference.

    Or maybe you just don't know it happens. :rolleyes:

    When a router disconnects you from 5GHz network your notebook will most likely automatically reconnect you to 2.4 GHz network (which is still working).
    If that doesn't happen your 5GHz SSID will reappear on a new channel after 1 minute and your computer will re-connect to it.

    And there is no point going to router settings to check the channel - UI doesn't get updated by the radio driver.
    If you chose channel 36 and you ended up on channel 122 as a result of DFS intervention, your router's GUI will still show 36. The only way to check is to use a network scanning software.

    9. What can I do?

    Not much really but when upgrading to 160MHz router buy one that supports 80+80 MHz non continuous channels.
    If this option is not available, you will not be able to avoid DFS channels.

    Also make sure to research what channels are supported - 80+80 needs to consist of lower channels an upper channel to avoid DFS ones. If your router supports lower and middle channels but not the upper ones, that won't help either.

    Also in some countries like Japan, Israel or Turkey upper channels are not available by law anyway.

    And in case you think that you can just choose a different country from a drop-down list to circumvent that - it might not be the case. Some wireless devices ignore that setting.
    I have one Wi-Fi card that completely ignores location set in driver advanced settings and goes with whatever location it has in its firmware. I also own a US bought Linksys router that will not accept the fact that I don't live in the US. Location is set in its eprom along with Wi-Fi transmission power tables and it just won't budge regardless of what you do.

    While it's still not clear if Intel 9260/Killer 1550 support non-continuous 80+80MHz channels, if it does you're in luck, if it doesn't some other card will come along and replacing a $25 card is much easier than a $250 router.

    Any questions, clarifications are welcome.
     
  2. nosauce

    nosauce Notebook Consultant

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    Thanks @downloads! This is very informative and I feel like it clarifies and pieces together a lot of the bits and pieces of knowledge about 160MHz that I've picked up here and there.

    It's sad how we own these cards, and we don't know what it's capable of. I assume the specification doesn't state it clearly, because the 1550 is touts 160MHz as a selling point, but I guess they don't specify which type?

    Let me make sure if I'm following you correctly. You're saying...
    1. that if the router doesn't support continuous 160 (only 80) then as long as the wifi card supports 80+80 we can use discontinous 160
    2. if the router supports some sort of discontinuous 160 then the wifi card doesn't have to support 80+80? and we can still use discontinuous 160?

    Do you know if NetGear R9000 is capable of 80+80. I read in one post over at netgear forums that it does, but then why is it that the router works only at low channels? and constantly disconnects? That sounds like continuous 160
     
  3. downloads

    downloads Super Moderator Super Moderator

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    @nosauce

    1. If the router just supports 80MHz there is no way for it to do 80+80 MHz. Radio has to be capable of doing that so older routers that just supported 80 MHz won't do 80+80 and there is nothing resembling link aggregation here.
    In order to be able to use 80+80 both router and card have to be capable of explicitly that.

    2. That's the same as above - if the router supports discontinuous 160 (80+80) than the card had to be able to support that as well for it to work.

    Netgear is capable of 80+80 for sure but I don't know how well does that work. Typically 80+80 would be better than 160 because in theory you could do both continuous 160MHz (by choosing neighboring channels) and discontinuous 160 by choosing two 80MHz that are apart, that said I can't test that with my WRT3200ACM/WRT32X as I don't have an option to do 80+80 to begin with.
     
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  4. Aivxtla

    Aivxtla Notebook Evangelist

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    Continuous 160Mhz is basic, nosauce. It’s the 80+80Mhz split bonding combining uppper and lower channels (Avoids DFS at least in US) is the one that the 9260ac doesn’t seem to support. The QCA9984 supports 80+80 split bonding in addition to contiguous 160Mhz. That’s the WiFi chip in the R7800 and R9000.
     
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  5. downloads

    downloads Super Moderator Super Moderator

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    @Aivxtla Does the R9000 support DFS channels? I seem to remember that smallnetbuilder said it did not. Is that correct or was it just some early firmware issue?
     
  6. Aivxtla

    Aivxtla Notebook Evangelist

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    It does there were updated FCC permission requests by Netgear later on. Even the new R9000 revision has DFS testing (Only difference with new revision according to FCC filing is removal of unused Bluetooth chipset). However I don’t know if it’s selectable in firmware. I gave mine away after the beta.
     
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  7. downloads

    downloads Super Moderator Super Moderator

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    Yeah I have a Bluetooth chipset in my router as well. Very useful - to the point where neither driver nor firmware for it are even present in the router's firmware ;)
     
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  8. Aivxtla

    Aivxtla Notebook Evangelist

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    I wonder how much design and underlying firmware work is really done by the actual contracted manufacturers ie Delta Networks, Foxconn etc rather than the brands Netgear/Linksys etc.

    Foxconn aka Hon Hai Precision (Taiwan) just bought Linksys, might actually be beneficial.
     
  9. downloads

    downloads Super Moderator Super Moderator

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    So I bought a router from Linksys who had been bought by Belkin who now has been bought by Foxconn that is in fact Hon Hai Precision. Yap. Crystal clear :cool:
     
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  10. t456

    t456 1977-09-05, 12:56:00 UTC Moderator

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    That's just ... idiotic.

    I've done some batch-analysis work using weather data gathered by such radars (HDF5) and they normally operate on 5 minute intervals or less. And even if they were using 1h intervals; what's the point of re-trying the same band over and over again? That radar won't switch bands or move lock-stock-and-barrel any time soon ...

    More humor from a Cisco sheet:
    So let's say channel 108 and 136 both have radar interference;
    1. Listens for 1m on dfs-required 108, finds radar and switches to random new channel
    2. Listens for 1m on dfs-required 138, finds radar and switches to random new channel
    3. Listens for 1m on dfs-required 108, finds radar and switches to random new channel
    4. Listens for 1m on dfs-required 138, finds radar and switches to random new channel
    5. ...
    Hmm ... maybe that explains the weird 30-minute black-list ...

    Do see the need for radar-avoidance though. Certain squares in our grids supposedly see excessive rainfall peaks over and over again, but these are obviously caused by interference. The trouble then is that this makes sewage load and surface drainage predictions completely unreliable for these areas. And that's just the known unknowns; the unknown unknowns have far greater consequences.

    However, this DFS-scan method is an absurdly blunt instrument. These (weather) radars are known, relatively static quantities and there's not that many of them. A simple IP traceroute/ping query to a bunch of pre-set IPs (e.g., one for and at each radar location) and you'd know the rough distance of the router to the nearest radar within a second. Next, send a magic packet to that radar's IP and you'd know the frequencies to avoid and blacklist. Could make the query mandatory, if so desired, but you'd only need to do this once after the router boots; that dish isn't going anywhere. Might even force a weekly check-up, just in case a new one is being built or the nearest one switched frequencies (also for any new, changed or disused IPs). And even then you'd have a grace time; the radar operator can be required to broadcast its new frequencies in response to packet-ing for at least a week prior to actually switching over to them. No need for that stupid 10-second-disconnect rule then.
     
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