Cisco Wireless Design

Hi Rene,

I don’t know if you can help me with problem correlate to cisco wireless design. Now we’re trying to use the wireless to replace the wired approach. However, I feel it’s pretty hard for me to calculate the AP coverage scope and capacity. I don’t know if you can share some input regarding this topic.

Thank you in advance.

Hello RSP.

This is a very open ended question, and it requires much discussion, but I can give you some general guidelines to go by that may help your decision making process.

The following are general issues that you need to determine depending on your specific deployment:

  1. First of all, why do you want to replace a wired network with wireless? Wired will almost always have higher robustness, availability and capacity. Use wireless ONLY if you absolutely need the mobility it provides or if running cables is absolutely not an option. If your users will be non-mobile PCs, don’t use wireless.
  2. If wireless is still the option of choice, then you’ll have to determine several things about the users:
    a) User density, which will determine the number of access points you’ll need per area
    b) What services will the users be using? This will determine the kind of throughput you require per user.
    c) Will the deployment be indoors? If so, what kinds of materials are the walls, floors, ceilings made of? Is there much metal that will absorb the wireless signals?
  3. What frequencies will you use? The 2.4 GHz range is limited to 3 non overlapping channels, and if you have neighbouring networks, this might limit you even further. The 5 GHz range has many more channels available, however, the disadvantage is that some older user devices may not support it, and it has less penetrating power through walls and other obstacles such as human bodies as well! So you might require more APs

The following are options that the available technology can provide for you:

  1. If you will have more than 4 or 5 APs, it is a good idea to get a Wireless Controller rather than configure access points individually. The tipping point for others may be 6 or 7 APs, but all that depends on budget. The controller will allow you to configure your network from one central location rather than configuring each individual AP. With a floor plan and frequency scanning of the area using the access points, a much better coverage can be achieved. You can also configure user bandwidth limitations, access control and optimum frequency usage. Also, any changes in the network such as frequency usage by neighbouring networks can trigger an alert to the admin.
  2. Although many manufacturers boast a large number of users per access point, they never actually tell you how many. I’ve seen huge ranges such as 50 to 100 users per access point!! Is it 50 or 100?!?! There is no real answer. It depends on many factors including usage per user and what the users are doing at any specific moment. Remember that everyone connected to an access point is one huge collision domain WITHOUT collision detection mechanisms, unlike a wired solution using a switch where each user is alone within a collision domain. A general rule to follow is 20 users per access point. You may be able to get more, you may get fewer, depending on usage, but it is a very general rule of thumb that you can use.

These are just some things to think about. I hope this has been helpful!