[HOW TO] Diagnose Wireless Issues

Chaihana Joe

It looks like my neighbours favour the lower order channels, so I have moved to 11 (though I have a Netgear DGN1000, which also uses channel 7 when I select channel 11). It's possible that things have improved, though too early to say with confidence.

I hope you can also expand on the issue of hard coded IP addresses as a solution to possible DHCP problems. Beerhunter suggested this was best avoided, though I am still tempted and would like to know what the pitfalls might be.

beerhunter

DHCP will manage your IP Addressing perfectly well and whether one uses DHCP or Fixed Addressing has no effect on WiFi connectivity because that is done further down the stack.

The pitfalls of Fixed Addressing are that one needs to ensure that any Fixed Addresses are not within the DHCP Server's Address Pool and keep a record of the IP Addresses that one has allocated (the DHCP Server does that for DHCP) so as not to give two devices the same addresses.  (These things often get overlooked, especially as new devices are brought into the house and added to the network.)

I let DHCP do the work more than 99% of the time, using Fixed Addressing only in extremis.

beerhunter

Yes that is more accurate.

Kristian

I agree with Beerhunter about DHCP use for the home/SOHO, especually as you can reserve addresses in the home routers.

Another pit fall of static addresses is that the DHCP service also gives out DNS server info (amongst other info), so if you change the DNS servers you use, or your ISP does (DHCP to your router's WAN interface), these changes are not propagated to the static devices and you'll have to change these yourself.

Chaihana Joe

OK, having moved from channel 5 to channel 11 and given it a few days, I'd say that we're getting disconnects pretty much as often as before the change.

What I hadn't twigged before, is that Homeplug connected devices are losing their connections at the same time as devices using wireless connections.

For a bit, this made me think the router was a source of the problems. The router is a Netgear DGN1000, which we bought recently to replace a Netgear DG834. We made this change because we thought the DG834 might be faulty - we were having the same connection dropouts. But it seems unlikely that both routers are faulty in the same way.

So now I'm thinking there may be a problem with the wiring on the far side of the router. Which takes us well off topic for a thread devoted to wireless issues. But thanks for your help, anyway guys.

Perhaps another thread on fault finding beyond the router/modem is called for?

chuckles1001

Great good info given

mickevh

That may be a reference to the "40MHz" AKA "channel-bonded" modes available in 802.11N.

The 2.4GHz band channel numbers - 1 through 13 - are just "labels" for a particular set of radio frequencies. These frequencies are 5MHz apart. C14 is a bit of an oddity and IIRC not available in Europe, so lets ignore that one.

So the channel numbers are essentially a shortcut to avoid having to remember what the actual radio frequencies are - C6 is easier to remember that 2.437GHz. Wiki's article contains the actual numbers for anyone interested.

Wifi transmissions don't use a "single" radio frequency like music radio stations (hence the "bell curves" InSSIDer sometimes draws are somewhat inaccurate.)

Wifi uses a "set" of 50 or so radio frequencies 0.3125 apart spaced out over 10MHz (ish) either side if the nominal centre frequency. Hence, a wifi radio "tuned" to C6 is also transmitting in the frequencies denoted as C4,C5,C6,C7,C8. Again, Wiki's 802.11 article illustrates this quite nicely. These are known as "20MHz" channels as used by 802.11 A/B/G.

802.11 N, in addition to 20MHz channels, allows "40MHz" channels, basically doubling(ish) the number of sub carriers which thence means the radio transmissions extend even further either side of the nominal centre frequency. So using 40MHz mode tuned to C6, the radio is transmitting sub carriers in the range C2 thru C10.

This is why 40MHz mode 802.11N can be a bit of a pain in the 2.4GHz waveband - 40MHz modes are taking up a lot of the available frequency spectrum and given the ever increasing number of wifi devices in the world, it's getting hard to find that much spectrum all to yourself (or at least, sufficiently free of interference to be reliable) unless you live in the middle of a large field.

For this reason, some people restrict their 2.4GHz "N" to use only "20MHz" channels to get a more reliable connection, albeit with a penalty of lower link rate.

EDIT 2015:  The "AC" Wi-Fi protocol extends the "channel bonding" ideal even further by availing  80MHz and 160MHz "wide" channels. The details of how the "extra" channels are placed above/below the nominal channel are a little complex, so I won't describe them here, but doubtless Google is your friend for anyone that really wants to know.

beerhunter

Just a quick point about how 'good' the WiFi is on ISP supplied routers.

Many people post on these forums asking for a recommendation for a new router because the ISP supplied one is "rubbish".  Their problem is usually caused by the classic channel conflict and so using inSSIDer or Kismac will help solve it without the need for new kit.

As evidence for this point of view: most of the subscribers around me (deepest Hampshire) use the ISP supplied router, including lots of BT Home Hub 1.0/1.5s & 2.0s.  WiFi problems around here are unknown.  (I mean that literally.) I refuse to believe that the ISPs send us all the good kit and supply the "rubbish" to the more populated areas.  Which must mean that the reason for our better WiFi performance is simply that our houses are further away from each other and thus interference.

Iccz

Couldn't agree more, there seems to be a lot of users spending money on new modem/routers when they don't need to. The main reason I see people buying them is because they believe the wireless or connection will be better with a different one. I can understand if someone requires features that are not provided on the ISP provided one but otherwise it seems like a waste of money. Generally wireless issues can be solved quickly and easily.
I think there are a lot of people who believe that a "known brand" like Netgear, D-Link or Belkin will be better because of the name and because it's going to cost money, I disagree - no ISP will provide duff kit as that would increase support calls and in turn their operating costs.

charleyfarley

This is a nice sticky and one that i expect thousands to visit and learn from.  Good work chaps

I hadn't had any problems with my broadband connection until i recently installed an old AppleTV.  It works fine wirelessly most of the time but since installing i have seen a fair few dropped signals on my 2wire HG1800... however, in my limited experience i sense interference and not hardware, this thread adds confidence to my convictions.  Thank you

Is there a simple to follow instruction for Kismac somewhere?