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Bandwidth/Simultaneous Users Question

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Anonymous
October 5, 2004 10:43:32 PM

Archived from groups: alt.internet.wireless (More info?)

I was wanting to know how bandwidth is distributed on 802.11g wireless
access points amongst simultaneous users? Am I incorrect in assuming
that if I need for each one of my 2000 simultaneous users to have
reliable duplex speeds of 750Kbps I would need a 2000 x 750Kbps = 1500
Mbps? Or if each 54Mbps 802.11g access point supports 250 SU's that
each user has only 216Kbps available to each of them? Also if I have a
3Mpbs T3 line hooked into a 802.11g 54Mbps wireless access point can I
really expect speeds of 54Mbps or am I limited to the 3Mbps to its
internet backhaul. I don't see how a wireless access point can speed
up data rates but perhaps that's one of the secrets of the radio
technology that's involved.

Just looking for some clarification. Thank you all for your input.

Jacob
Anonymous
October 6, 2004 6:48:12 AM

Archived from groups: alt.internet.wireless (More info?)

jacob_chaney@hotmail.com (Jacobs Scooter) wrote in
news:298e35bd.0410051743.44a7fdab@posting.google.com:

> I was wanting to know how bandwidth is distributed on 802.11g wireless
> access points amongst simultaneous users?

Use split available bandwidth. An 802.11g AP provides about 35mbps of
bandwidth.


> Am I incorrect in assuming
> that if I need for each one of my 2000 simultaneous users to have
> reliable duplex speeds of 750Kbps I would need a 2000 x 750Kbps = 1500
> Mbps?

You're calculating guaranteed speed... but in reality you don't need
that much speed. Not everyone will be logged in at once, and not
everyone will be transfering constantly. I'm not sure the exact
calculation to use though...

> Also if I have a
> 3Mpbs T3 line hooked into a 802.11g 54Mbps wireless access point can I
> really expect speeds of 54Mbps or am I limited to the 3Mbps to its
> internet backhaul.

You're limited to 3mbps to the Internet. However, interally you'll be
able to hit ~35mbps. 802.11g never really hits 54mbps.

> I don't see how a wireless access point can speed
> up data rates but perhaps that's one of the secrets of the radio
> technology that's involved.

???

The "speed-up" is only between the client and the access point. From the
access point to the Internet... that can only be sped up by your network
administrator or your internet connection.
Anonymous
October 6, 2004 9:04:00 AM

Archived from groups: alt.internet.wireless (More info?)

On Wed, 06 Oct 2004 04:20:23 GMT, Jeff Liebermann
<jeffl@comix.santa-cruz.ca.us> wrote:

>My guess(tm) is that you'll have no more than 10%
>loading and can easily live with 128-256Kbits/sec per user per access
>point when active. You'll be stuck with using 802.11b at 5.5Mbits/sec
>because of the increased range an penetration of the lower speeds.
>That gives you about 200 users per access point. If you put 3 radios
>on each poletop, that will give you 600 users per hot spot. If you
>try to deliver anything more or faster, you will have problems. The
>aggregate bandwidth at each poletop will be about 6-10 Mbit/sec which
>can easily be handled by just about any kind of transparent bridge
>(that can handle 600 MAC addresses). Your backhaul to the ISP will be
>6-10Mbits/sec times the number of hot spots. Note that this is only a
>guess based upon what little information you've supplied.

Oops. I forgot to mention that my back-o-de-envelope guess is based
on 100% bandwidth utilization, with no retransmissions, no
interference, and 100% efficiency. That never happens. You will get
collisions, interference, retrans, and other airtime burners. You
also don't wanna use all your bandwidth all the time or you end up
with really bad performance. Figure 50% or less is good safe value
with room for some overhead. That's about 100 users per access point
or 300 users per hot spot.


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# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# jeffl@comix.santa-cruz.ca.us
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