Multiple APs

Hi all,

We need an 802.11b/g network to serve 50 clients. We have two WAPs,
each of which can handle up to about 30 clients. Can somebody comment
on the pros and cons of setting them to the same or different channels?

Perhaps pros and cons is the wrong term, more like what functionality is
gained and lost with each method.

I am aware that if they are on different channels, the channels need to
be well seperated.

Antony

Antony Gelberg <(E-Mail Removed)> hath wroth:

>We need an 802.11b/g network to serve 50 clients. We have two WAPs,
>each of which can handle up to about 30 clients.

Could you kindly disclose the maker and model of your existing WAP's?

Does it really have a hard limit of 30 users or is that the estimated
number of users per access point based on "typical" traffic?

The number of users served are fairly simple to estimate:
100 users doing light surfing and email.
10 corporate or business users.
1 file sharing user.

>Can somebody comment
>on the pros and cons of setting them to the same or different channels?

Yes, I can.

>Perhaps pros and cons is the wrong term, more like what functionality is
>gained and lost with each method.

All on one channel with same SSID:
Advantages:
- Possible seamless roaming if the client support it.
- Least amount of interference to neighboring systems.
- Minimum user configuration issues.
Disadvantages:
- Maximum mutual RF interference. Needs physical isolation.

All on one channel with different SSID:
Advantages:
- Users can intentionally select a specific access point.
- Least amount of interference to neighboring systems.
Disadvantages:
- Seamless roaming is impossible.
- Somewhat complex user configuration.

Different channels with same SSID:
Advantages:
- Seamless roaming is possible with a smart client.
- Least amount of mutual interference from your own access points.
Disadvantages:
- Increased chance of interference from other co-channel users.
- Simple user configuration. Clients will scan for SSID.

Different channels with different SSID:
Advantages:
- Easy troubleshooting and identification of WAPs.
Disadvantage:
- Users must intentionally select their access point. No roaming.
- Most complex configuration for users.
- Increased chance of interference from other co-channel users.

>I am aware that if they are on different channels, the channels need to
>be well seperated.

You don't have much choice in channels. 1, 6, and 11 are the only
non-overlapping channels. If you select a channel in between these,
you risk receiving interference from both adjacent channels.

This is worth reading completely:

ftp://download.intel.com/business/bs...nt/hotspot.pdf
See 5.2.3.1 on channel re-use.

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:
> Antony Gelberg <(E-Mail Removed)> hath wroth:
>
>
>>We need an 802.11b/g network to serve 50 clients. We have two WAPs,
>>each of which can handle up to about 30 clients.
>
>
> Could you kindly disclose the maker and model of your existing WAP's?

Sure, Netgear WAP102.
http://www.netgear.com/products/details/WAG102.php

> Does it really have a hard limit of 30 users or is that the estimated
> number of users per access point based on "typical" traffic?
>
> The number of users served are fairly simple to estimate:
> 100 users doing light surfing and email.

I think that this will be the main use case. Netgear pre-sales has just
told us that the theoretical (as in defined by the standard, not
vendor-specific) maximum per channel is 32 users, and the limit on this
AP is more like 15 users in practice. How does that reconcile with your
figure of 100?

> 10 corporate or business users.
> 1 file sharing user.
>
>
>>Can somebody comment
>>on the pros and cons of setting them to the same or different channels?
>
>
> Yes, I can.
>
>
>>Perhaps pros and cons is the wrong term, more like what functionality is
>>gained and lost with each method.
>
>
> All on one channel with same SSID:
> Advantages:
> - Possible seamless roaming if the client support it.
> - Least amount of interference to neighboring systems.
> - Minimum user configuration issues.
> Disadvantages:
> - Maximum mutual RF interference. Needs physical isolation.
>
> All on one channel with different SSID:
> Advantages:
> - Users can intentionally select a specific access point.
> - Least amount of interference to neighboring systems.
> Disadvantages:
> - Seamless roaming is impossible.
> - Somewhat complex user configuration.
>
> Different channels with same SSID:
> Advantages:
> - Seamless roaming is possible with a smart client.
> - Least amount of mutual interference from your own access points.
> Disadvantages:
> - Increased chance of interference from other co-channel users.
> - Simple user configuration. Clients will scan for SSID.

Is simple user configuration not an advantage?

>
> Different channels with different SSID:
> Advantages:
> - Easy troubleshooting and identification of WAPs.
> Disadvantage:
> - Users must intentionally select their access point. No roaming.
> - Most complex configuration for users.
> - Increased chance of interference from other co-channel users.
>
>
>>I am aware that if they are on different channels, the channels need to
>>be well seperated.
>
>
> You don't have much choice in channels. 1, 6, and 11 are the only
> non-overlapping channels. If you select a channel in between these,
> you risk receiving interference from both adjacent channels.
>
> This is worth reading completely:
>
> ftp://download.intel.com/business/bs...nt/hotspot.pdf
> See 5.2.3.1 on channel re-use.

Reading it now.

Antony Gelberg <(E-Mail Removed)> hath wroth:

>> Could you kindly disclose the maker and model of your existing WAP's?
>
>Sure, Netgear WAP102.
>http://www.netgear.com/products/details/WAG102.php
>
>> Does it really have a hard limit of 30 users or is that the estimated
>> number of users per access point based on "typical" traffic?

Hmmm... Looking at the above data sheet, it proclaims:
"It supports up to 128 simultaneous wireless clients and
client types within the same coverage area."
There may be a 30 user limit in the bridge to bridge mode, but not the
access point mode.

>> The number of users served are fairly simple to estimate:
>> 100 users doing light surfing and email.
>
>I think that this will be the main use case. Netgear pre-sales has just
>told us that the theoretical (as in defined by the standard, not
>vendor-specific) maximum per channel is 32 users, and the limit on this
>AP is more like 15 users in practice. How does that reconcile with your
>figure of 100?

See above quotation from the data sheet. Netgear pre-sales support is
wrong. Actually, I'm not even sure 128 is the real upper limit for
simultaneous connections. In a past life (about 7 years ago), I did
quite a bit of bench testing to see how many simultaneous users and
connections could be handled by various access points. Unfortunately,
I didn't test this wireless access point. Many of the units tested
would literally roll over and die when faced with too many MAC
addresses. It's really a question of how much memory is available for
internal tables and what algorithm is used to clear the tables when
approaching overflow. Sorry, I'm not at liberty to disclose models
and numbers.

I've actually deal with a system that had about 100 simultaneous
connections with a T1 backhaul. The assumption is that not everyone
is doing something at the same time. That's what I mean by "light
surfing" and email. With the proper application of bandwidth
management (i.e. QoS) to prevent any one user from hogging all the
available bandwidth, it is possible to run with 100 simultaneous
users.

However, if it's an office environment, forget it. Office computers
are always doing something. The average useage is much higher. Users
expect instant response time. My guess is about 10-20 office users
per AP maximum.

The one user file sharing is not a joke. Most file sharing
applications are designed specifically to maximize thrutput, which
means opening up huge number of simultaneous streams. That will hog
literally all the bandwidth, all the buffer space available, and flood
any cache in between.

>Is simple user configuration not an advantage?

Oops. Sorry. It should be listed as an advantage.

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558