Thursday, January 7, 2016

Questions about wireless access points and how many users you can expect to have on each one.

     Over the last few days, I have read dozens of posts pertaining to the number of users an access point can have on it at any given time. The responses have been overwhelmingly diverse to say the least but one thing is certain in all of them... There is no concrete answer to this question. In fact, most of the answers folks were providing had a lot to do with a manufacturer's chipset or the 802.11 protocol's statement allowing for 2007. The truth is that this is a loaded question waiting on hundreds of educated wireless experts to tear it apart. I am going to make a few statements about this question and then ask those experts to contribute to the information.

     First off, there are only suggestions from various manufacturers of 802.11 wireless access points as to how many users can be on each access point. These suggestions are no less than a sales point to allow a number to be mentioned. You can not designate a number of users per access point until you at least answer several other questions:

1) What applications will you be using on your wireless network?

2) What security measures will be in place on your wireless network?

3) What does the environment look like and what is in the environment that could effect signal?

4) How much area are you wanting to cover with a single access point in this environment?

5) What data rates are you going to allow on the wireless network?

and the list goes on and on..... but these are a few questions that NEED to be answered.

     The application is both processor and bandwidth reliant. What I mean is.... an application may require a lot of processing power and bandwidth, depending on the application. These two factors alone weigh heavy on the individual access point when you are talking multiple clients using the same application on the same access point.

     Securing the network takes processing power and bandwidth overhead. Off course you can avoid the use of this overhead by not using any security but your network will not be safe at all.

     The environment plays a role as well. Interfering devices can cause a higher noise floor in cases and the end result would be any of many things including rate shifting,  and using a less efficient modulation type to obtain a stable connection.

     If you want to cover a lot of area with your access point, chances are you are going to turn up the power by increasing the transmit power, using more powerful antennas, or a combination of the two. This could be tricky because of client power limitations and it could result in an array of issues. The Near/Far effect could occur, contention for the network could take longer due to the amount of users now in the cell and the data rates they are connected at. (just a few... I want to leave plenty of room for input here).

    Data rates are a big topic. If data rates are not controlled based on applications used, then the network is opened up to a multitude of issues. Clients closer to the access point will connect at a better modulation type and better data rate while those clients further away will use a different modulation type in order to secure an efficient connection resulting in lower data rates. If devices are allowed to connect at "B rates", then the whole network suffers the consequences of having to slow down to sync up with the slower slot times used by the single device utilizing the "B data rate".

     All of these are factors that play with the math. If you are going to use wireless as a network connection, you must assess the needs, applications, security, etc.. before you determine how many users you feel will efficiently operate on each access point.

Brett Hill, CWNE #147

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