On 22/08/10 02:42, Tim wrote:
> Tim:
>>> All your wireless devices transmit on the same channel.
> g:
>> yes and no. depends on manual assignment.
> Well, generally speaking, your access point only works on one channel,
> and all the clients use the same one. If you have two access points on
> the same channel, such as across a large site, your clients use the one
> with the strongest signal, with the clients being on the same channel
> two. But it's less problematic to have your access points on different
> channels (less likely to have spots where reception won't work), and the
> clients will change channels to suit the access point they're using.
> Generally speaking, an access point doesn't change the channel that it's
> using, after its setup.
Here's an interesting paper on "wifi" interference:
http://www.cisco.com/en/US/docs/wireless/technology/channel/deployment/guide/Channel.html#wp134132
Notice that the channel spacing is 5 mHz but the bandwidth is more
like 22 mHz. And I suspect that since these are spread spectrum
devices that the effect of interference to data is not as simple as
it would be between two broadcast stations having mutual
interference, probably less a problem for the data links.
And if I add a second router to the system I would most likely add
to the interference problems and ultimately reduce my end to end
data transmission speed?
Not only that but installing DD-WRT on this one which looked like a
klunk initially, has completely transformed it into a usable device,
possibly better than what I have been using. I have made no
measurements to prove anything but I think data is being transferred
faster.
We are in a rural location pretty well isolated from neighbors and I
don't think there are any sources of interference outside of our own
system except possibly the microwave oven and I imagined that would
just slow down things for the moment it was running, never very long.
> Going from what I understand of Bob's setup, he's got one access point
> and several clients. Those clients may have inbuilt wireless, or they
> may connect to a dongle/box to provide wireless networking. In that
> case, they would all be on the same channel. Even if he connected a
> separate DHCP server, it would be yet another client, rather than act as
> an access point (providing networking service to other clients).
>
Presently I have one access point and most of the clients are radio
to ethernet bridges. My equipment in this room is tied to a gigabit
switch and to the remainder of the LAN via a Buffalo ethernet to
radio adapter that is supposed to be dual band [2.4/5.x gHz] and
mode "n" capable. This modified router is supposed to have similar
capabilities without gigabit switching. And of course the satellite
ISP speeds are mediocre as such things go, claim 1.5 mb/s down, and
that only on a good day, upload is much slower. The fixed desktop
stations, video cameras, etc. are setup the same way, of course the
portables, iPods and such have whatever wireless is built in to them.
>>> With wired networking, through a switch or router, many devices can all
>>> talk simultaneously, if they're each talking to different devices.
>> again, yes and no. with a switch, yes.
>>
>> with a router, no. again, first to transmit/first heard.
> Only if you're talking about /through/ the gateway, or different clients
> wanting to talk with the same device. Half a dozen clients all talking
> to each other, or anything else within the LAN, can do so
> simultaneously. i.e. Pairs of chatting devices that aren't talking to
> something else that's busy.
>
>> for wireless, what is needed, if not already, is ability for each interface
>> to monitor in a delayed channel switch scan mode.
>>
>> when a signal is received, interface would listen for it's ip. if being
>> 'called', it then replies and communications are established.
>>
>> if interface needs to communicate, it would first scan for an open channel,
>> then send destination ip address and listen for reply.
> Generally, when there's more than one access point available to you,
> whether they're part of the same LAN or not, your client will do one of
> a few things:
>
> Connect to one, and ignore all the others, until /you/ quit.
>
> Use the same one as last time.
>
> Use the one with best reception that it's authorised to use.
>
> Switch between access points if reception drops off the current one.
>
> Use the one the user manually selected.
>
> What isn't going to happen, with the usual way things run, is:
>
> To connect and disconnect while idle. Once it's connected to one, it
> keeps using the same one for the whole session, unless a problem crops
> up. NB: I'm not talking about continuous RF transmission, I'm
> talking about continuous association with the same access point.
>
> To switch access points if the one that you're currently set up to use
> is too busy.
>
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