Multi-AP WiFi best practice

Slightly OT, so I apologise, but this is the closest group, I think.

I visit a school that, like many, has a 'notebus' - a trolley
containing 16 laptops that is pushed to a classroom for the pupils'
use. They complain of a frequent inability to logon and very poor
speeds.

When I checked from my laptop I could see 12 APs and could connect to
every one of them. They are all configured identically (same SSID and
security settings) but an attempt has been made to spread the channels
around.

A walk around the school showed 2 APs in every classroom. The APs are
all Zyxel G570U devices that can be set up in many ways (WDS etc.) but
are all set up as wired APs.

So, how would a WiFi expert set this network up? I have considered
changing half of the APs to another SSID,and changing half of the
laptops to use the new one, thus avoiding all 16 using the same AP
(which is a risk otherwise) but is there any other guidance the sages
herabouts can offer?

And how to force XP to wait until the connection is established before
logging on? At least I assume this is what is preventing users from
logging on when their credentials have not been cached (it's a AD
domain-based RM CC3 network).

On Nov 4, 12:30 pm, k...@birchanger.com wrote:
> Slightly OT, so I apologise, but this is the closest group, I think.
>
> I visit a school that, like many, has a 'notebus' - a trolley
> containing 16 laptops that is pushed to a classroom for the pupils'
> use. They complain of a frequent inability to logon and very poor
> speeds.
>
> When I checked from my laptop I could see 12 APs and could connect to
> every one of them. They are all configured identically (same SSID and
> security settings) but an attempt has been made to spread the channels
> around.
>
> A walk around the school showed 2 APs in every classroom. The APs are
> all Zyxel G570U devices that can be set up in many ways (WDS etc.) but
> are all set up as wired APs.
>
> So, how would a WiFi expert set this network up? I have considered
> changing half of the APs to another SSID,and changing half of the
> laptops to use the new one, thus avoiding all 16 using the same AP
> (which is a risk otherwise) but is there any other guidance the sages
> herabouts can offer?
>
> And how to force XP to wait until the connection is established before
> logging on? At least I assume this is what is preventing users from
> logging on when their credentials have not been cached (it's a AD
> domain-based RM CC3 network).

Hi
Why not have a unique wireless AP on the trolley and plug that into a
network port in the room its used in?
Al

(E-Mail Removed) wrote:

> Slightly OT, so I apologise, but this is the closest group, I think.
>
> I visit a school that, like many, has a 'notebus' - a trolley
> containing 16 laptops that is pushed to a classroom for the pupils'
> use. They complain of a frequent inability to logon and very poor
> speeds.

Start by turning off all bar one of the APs and laptops, and test
connectivity. Then gradually re-add laptops and APs and see what causes a
drop in performance.

> When I checked from my laptop I could see 12 APs and could connect to
> every one of them. They are all configured identically (same SSID and
> security settings) but an attempt has been made to spread the channels
> around.

It could be possible that they just have too many APs. If the APs are
adjacent to each other and are on overlapping channels, then you'll see
worse performance rather than better. Directional antennae on the APs might
help.

> A walk around the school showed 2 APs in every classroom. The APs are
> all Zyxel G570U devices that can be set up in many ways (WDS etc.) but
> are all set up as wired APs.

Having them wired and set up as ordinary APs will give you the best
performance [well, better than WDS anyway]. Obviously not as good as wired,
but presumably that's not an option otherwise they'd be using it. Make sure
that if any are set up with WDS that you have STP enabled to break any
loops.

> So, how would a WiFi expert set this network up? I have considered
> changing half of the APs to another SSID,and changing half of the
> laptops to use the new one, thus avoiding all 16 using the same AP
> (which is a risk otherwise) but is there any other guidance the sages
> herabouts can offer?

Make sure that adjacent APs aren't on overlapping channels. Obviously with
only three non-overlapping channels you might struggle. If that's the case,
try turning some of the APs off and see if that improves things.

--
<http://ale.cx/> (AIM:troffasky) ((E-Mail Removed))
13:04:29 up 2 days, 5:49, 2 users, load average: 0.15, 0.28, 0.27
50,000 watts of funking power

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>
> And how to force XP to wait until the connection is established before
> logging on? At least I assume this is what is preventing users from
> logging on when their credentials have not been cached (it's a AD
> domain-based RM CC3 network).

Hi - I understand Active Directory domains (I administer a few) but I've
never heard of "RM CC3 network" - off to Google I go.

With XP you can use a group policy to disable Fast Logon Optimization. See

http://support.microsoft.com/kb/305293

The policy setting you're after is

Computer Configuration\Administrative Templates\System\Logon\ Always wait
for the network at computer startup and logon

You can either link a GPO to an OU in AD containing your workstations or you
can deploy the setting individually in the local policy of each of
workstation.

hth


--
Peter <X-Files fan>

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Slightly OT, so I apologise, but this is the closest group, I think.
>
> I visit a school that, like many, has a 'notebus' - a trolley
> containing 16 laptops that is pushed to a classroom for the pupils'
> use. They complain of a frequent inability to logon and very poor
> speeds.
>
> When I checked from my laptop I could see 12 APs and could connect to
> every one of them. They are all configured identically (same SSID and
> security settings) but an attempt has been made to spread the channels
> around.
>
> A walk around the school showed 2 APs in every classroom. The APs are
> all Zyxel G570U devices that can be set up in many ways (WDS etc.) but
> are all set up as wired APs.
>
> So, how would a WiFi expert set this network up? I have considered
> changing half of the APs to another SSID,and changing half of the
> laptops to use the new one, thus avoiding all 16 using the same AP
> (which is a risk otherwise) but is there any other guidance the sages
> herabouts can offer?
>
> And how to force XP to wait until the connection is established before
> logging on? At least I assume this is what is preventing users from
> logging on when their credentials have not been cached (it's a AD
> domain-based RM CC3 network).

If you give me the telephone number for the school I will be happy to give
them a quote for correcting the system. It will save a lot of time and
effort.
Why have they asked you if you don't know much about computers?

On 04/11/2007 16:54, TKelly wrote:

> If you give me the telephone number for the school I will be happy to give
> them a quote for correcting the system. It will save a lot of time and
> effort.
> Why have they asked you if you don't know much about computers?

Oh yes, being condescending towards someone is a very good way to get
them to hand one of their customers over to you ...

On Sun, 04 Nov 2007 05:01:55 -0800, al <(E-Mail Removed)>
wrote:

>On Nov 4, 12:30 pm, k...@birchanger.com wrote:
>> Slightly OT, so I apologise, but this is the closest group, I think.
>>
>> I visit a school that, like many, has a 'notebus' - a trolley
>> containing 16 laptops that is pushed to a classroom for the pupils'
>> use. They complain of a frequent inability to logon and very poor
>> speeds.
>>
>> When I checked from my laptop I could see 12 APs and could connect to
>> every one of them. They are all configured identically (same SSID and
>> security settings) but an attempt has been made to spread the channels
>> around.
>>
>> A walk around the school showed 2 APs in every classroom. The APs are
>> all Zyxel G570U devices that can be set up in many ways (WDS etc.) but
>> are all set up as wired APs.
>>
>> So, how would a WiFi expert set this network up? I have considered
>> changing half of the APs to another SSID,and changing half of the
>> laptops to use the new one, thus avoiding all 16 using the same AP
>> (which is a risk otherwise) but is there any other guidance the sages
>> herabouts can offer?
>>
>> And how to force XP to wait until the connection is established before
>> logging on? At least I assume this is what is preventing users from
>> logging on when their credentials have not been cached (it's a AD
>> domain-based RM CC3 network).
>
>Hi
>Why not have a unique wireless AP on the trolley and plug that into a
>network port in the room its used in?
>Al

Some schools do just that (but usually 2 APs as it seems to be
axiomatic that you shouldn't try to use more than, say, 10 clients at
the same time).

On Sun, 04 Nov 2007 17:52:36 +0000, Andy Burns
<(E-Mail Removed)> wrote:

>On 04/11/2007 16:54, TKelly wrote:
>
>> If you give me the telephone number for the school I will be happy to give
>> them a quote for correcting the system. It will save a lot of time and
>> effort.
>> Why have they asked you if you don't know much about computers?
>
>Oh yes, being condescending towards someone is a very good way to get
>them to hand one of their customers over to you ...

So, in just a few hours, on a Sunday, I have had some very sensible
suggestions (plus a twat). Thanks to all (bar one - but if the twat's
as knowledgeable as (s)he claims then I suppose they may demonstrate
their ability by posting a constructive suggestion).

Your answers have reinforced what I thought - there's nothing
fundamentally wrong with the setup, but there are probably too many
APs. I will experiment by reducing them and seeing the results.
However politics makes it hard to simply turn some of them off. I will
also try splitting the network, as I suggested in my OP. The only
other users, apart from the notebus, are teachers' laptops - a maximum
of one per room and, in any case, normally connected by Ethernet.

I should have expanded the RM CC3 bit - it's Research Machines
Community Connect 3 and is based around Server 2000 or 2003 and
designed for schools. It manages applications, printers and so on,
almost entirely through GPOs. Problem is I'm reluctant to play with
the GPOs because I'm not sure what CC3 does in the background.

I am aware of the ability to manage fast logons, but have not played
with it in this school (see last paragraph). Partly this is because
Microsoft imply that fast logon is inhibited in a roaming profile
situation - this is not my experience with WiFi. Also there are
various articles around that imply that you CANNOT inhibit logon prior
to connect with WiFi unless you use 802.1x authentication - which
seems OTT.

But - thanks to you all.

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Slightly OT, so I apologise, but this is the closest group, I think.
>
try alt.internet.wireless

cross posted for the discussion.

> I visit a school that, like many, has a 'notebus' - a trolley
> containing 16 laptops that is pushed to a classroom for the pupils'
> use. They complain of a frequent inability to logon and very poor
> speeds.
>
> When I checked from my laptop I could see 12 APs and could connect to
> every one of them. They are all configured identically (same SSID and
> security settings) but an attempt has been made to spread the channels
> around.

sounds like the power levels are too high - too many APs with overlapping
signals is going to generate lots of interference.

the thing to remember is the PC driver switches APs - so the key is to find
a working driver that reliably finds the "stongest" signal.
>
> A walk around the school showed 2 APs in every classroom. The APs are
> all Zyxel G570U devices that can be set up in many ways (WDS etc.) but
> are all set up as wired APs.

simplest test is turning off 1 AP and see if things improve.
>
> So, how would a WiFi expert set this network up? I have considered
> changing half of the APs to another SSID,and changing half of the
> laptops to use the new one, thus avoiding all 16 using the same AP
> (which is a risk otherwise) but is there any other guidance the sages
> herabouts can offer?

the key is when you make a change - test it and compare results. This is
meant to be engineering, not black magic.

you have to wonder why have the complexities of wireless if you can just
have a small switch on the trolley and plug a cable in?
>
> And how to force XP to wait until the connection is established before
> logging on? At least I assume this is what is preventing users from
> logging on when their credentials have not been cached (it's a AD
> domain-based RM CC3 network).
--
Regards

(E-Mail Removed) - replace xyz with ntl

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Sun, 04 Nov 2007 17:52:36 +0000, Andy Burns
> <(E-Mail Removed)> wrote:
>
>>On 04/11/2007 16:54, TKelly wrote:
>>
>>> If you give me the telephone number for the school I will be happy to
>>> give
>>> them a quote for correcting the system. It will save a lot of time and
>>> effort.
>>> Why have they asked you if you don't know much about computers?
>>
>>Oh yes, being condescending towards someone is a very good way to get
>>them to hand one of their customers over to you ...
>
> So, in just a few hours, on a Sunday, I have had some very sensible
> suggestions (plus a twat). Thanks to all (bar one - but if the twat's
> as knowledgeable as (s)he claims then I suppose they may demonstrate
> their ability by posting a constructive suggestion).
>
> Your answers have reinforced what I thought - there's nothing
> fundamentally wrong with the setup, but there are probably too many
> APs. I will experiment by reducing them and seeing the results.
> However politics makes it hard to simply turn some of them off. I will
> also try splitting the network, as I suggested in my OP. The only
> other users, apart from the notebus, are teachers' laptops - a maximum
> of one per room and, in any case, normally connected by Ethernet.

[snip]

As others have suggested, wireless networking has the very severe limitation
that it is in effect a single collision domain for each AP, so having more
than a very few clients per AP per channel will be a serious performance
limitation. This will be especially noticeable if users have roaming
profiles and are allowed to store their documents within the profile - since
each profile can potentially be many tens or hundreds of Mbytes.

The other issue is political. I was involved for a while with a local
school because one of the governors asked me to try to resolve a
similar-sounding problem (a class of students could not all log on at once
at the beginning of a lesson, thereby wrecking any lesson plan that the
teacher had prepared). In this instance all the workstations were connected
via 100 Mbits/sec ethernet and a Gigabit backbone to a reasonably powerful
server, which was clearly not being significantly stressed. But the system
had evolved, rather than been designed. The school managed the budget, but
had nobody with the combination of relevant experience and management
ability to commission work. They bought in the major management service
from a privatised offshoot of what had been the county education authority
computer services department; and while there were some good principles
established in the system much of the everyday detail seemed to be
misguided. One craft technician was left with the responsibilty of
day-to-day mangagement - he had a good idea of the difficulties he faced but
was totally the wrong personality to get anything done.

My recommendation from this experience would be install a gigabit network
throughout and install diskless workstations for student use. Then you
stand a sporting chance of maintaining security and managing updates by
having all the workstations boot from the server via the network.

Also, I wouldn't entertain the idea of laptops anywhere!! I've just heard
of a school where trolleys of laptops were supposed to be locked away in a
secure room when not in use; this room was broken into (while there was a
dance or some such noisy event in progress) and the trolley used to move all
the laptops across the playing field to a waiting vehicle.

I am also very strongly of the opinion that computers add very little to the
chance of pupils actually learning anything - everywhere I've seen them
used, they have simply been a distraction. I doubt that many pupils even
learn they way around the keyboard - I'm sure formal typing lessons would be
more use! The quality of grammar and spelling demonstrated by the students
is abysmal, and there's very little idea of decent presentation of work.
The computer certainly does not show itself as an aid to communication.

I would seriously recommend getting rid of all the computers and buying in a
few more skilled teachers!

-- Graham J