gpg: failed to create temporary file '/var/lib/lurker/.#lk0x57d89100.hantslug.org.uk.14309': Permission denied
gpg: keyblock resource '/var/lib/lurker/pubring.gpg': Permission denied
gpg: Signature made Wed Mar 28 21:43:22 2007 BST
gpg: using RSA key ED1319F325A97448
gpg: Can't check signature: No public key
Cayenne-uk wrote:
> Why are channels 1,6 and 11 the only effective channels to use? As I
> mentioned, my router is set at 9 and can make a connection - but can I
> expect more trouble if I settle on this channel?
>
It's to do with frequency overlap. Basically the available spectrum in
the 2.4GHz band (the band used by 802.11b and 802.11g) is divided into a
number of notional sub-bands, called channels. In the US there are 11
channels allowed. The UK, Europe and Japan use the same 11 channels but
can also use 2 extra ones, making up 13 channels.
Each channel actually covers a small range of frequencies in the 2.4GHz
range, and they overlap with the two adjacent channels in each
direction. So channel 3 overlaps with channels 1, 2, 4 and 5. Channel 7
overlaps with channels 5, 6, 8 and 9. It should be fairly obvious that
the non-overlapping channels are 4 channels apart, so 1, 6 and 11. In
the UK we also have the option of 2, 7 and 12 or 3, 8 and 13. However,
as the US only has the choice of 1, 6 and 11 it is common to deploy
Wireless Access Points using those channels. (It is impossible to
provide 3D coverage of a space using just three channels - there is I
believe some complex maths to prove that statement too.
What happens if you /do/ use overlapping channels? Well, there will be
increased interference with your wireless signals. This will effect the
throughput of the WAP and wireless clients and will reduce the effective
bandwidth achieved. Some wireless network designers find that you can
use wireless channels with a three channel gap in the UK rather than
four (i.e. 1, 5, 9 and 13) as the frequency overlap is small enough not
to cause a large impact on bandwidth under most circumstances. This
obviously gives the designer a little more freedom and flexibility when
implementing wireless networks.
Of course, you don't have control over which channel your neighbours use
for their WAPs. You could go round and ask them to move to a different
channel. You might even want to explain why. However, it's probably just
easiest to change your WAP to the least congested channel and check to
see if another channel looks to be a better bet every so often. It's
also worth remembering that just because you are in range of your
neighbours wireless networks, that doesn't mean they are in range of
each other's. So they might not actually be noticing any interference,
even if they are looking.
Cisco have a good paper on channels at [1], but any good wireless
network design books should cover the same thing.
HTH,
Tony
[1]
http://www.cisco.com/en/US/products/hw/wireless/ps430/prod_technical_reference09186a00802846a2.html
