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Defining Your Technology Requirements

As you learned in Chapter 1, the three primary technologies available today are 802.11a, 802.11b, and 802.11g. Now it is time to decide which one fits your needs (or at least try). Before you can decide which technology to use, you first must answer more questions. As mentioned previously, there are many different types of WLAN uses and applications. These variations can cause major differences in WLAN designs.

One thing that is important to discuss here is the difference between 802.11b and 8702.11g, from the AP perspective. If the system being installed is a new purchase, you should use 802.11g APs. These support both 802.11b and 802.11g clients and are typically priced at the same level. In fact, the availability of 802.11b APs will start to diminish. However, 802.11b clients will be around for several years still because of the current ubiquity of laptops with embedded 802.11b radios.

As you move forward toward a decision regarding technology, answer the following questions:

What present applications will be used and what is their bandwidth requirement per user?

This question is vital. If you plan to use the network for simple network connection and average office-type applications (MS Office, e-mail, web browsing, database access, and so forth), the bandwidth of a normal 802.11b/g system will probably suffice (depending on the answer to the following question).

What is the average and maximum density of WLAN users in any given coverage area, and will this density increase over time?

You need to determine how many users will be in a given area, both on a routine basis and on a maximum-user basis. For the average office application (as defined by your answer to the first question in this list), you can get reasonable performance with 10 to 20 users per AP when using 802.11b data rates. For small-transaction applications with a low-bandwidth requirement, such as a stock trading floor or bar coding, the number of users per AP can increase dramatically. Remember that the aggregate throughput (not data rate) of an 11-Mbps 802.11b system is about 5.5- to 6-Mbps aggregate per AP (and the average throughput of a 802.11b and 802.11g mixed system, with an 802.11g AP, is about 8 Mbps).

Chapter 12, "Installing WLAN Products." Remember, however, that some 5-GHz AP antennas have limitations. In public-access sites, schools, health-care facilities, and other public mini-PCI interfaces. Because 802.11b is only 11 Mbps, a PCMCIA interface to the radio is perfectly acceptable. If you are moving to 802.11a (or 802.11g), however, you need Cardbus support or mini-PCI support, because a PCMCIA interface is not fast enough to provide a 54-Mbps data rate. If there will be an array of various client devices, interoperability will be a greater issue, which means you need to select an AP with the greatest degree of proven interoperability, from a company that has been deploying WLANs for a considerable amount of time.

What regulations govern the use of IEEE 802.11 in this region?

As explained Chapter 3, some countries still do not permit 802.11a systems. Other countries require the use of dynamic frequency selection and automatic power control (both of which are part of 802.11h) for 802.11a or other 5-GHz radio systems.

Other regulatory issues, such as Effective Isotropic Radiated Power (EIRP) limits, frequency allocation, and antenna limitations, can come into play as well. Even 2.4 GHz has many different regulations from country to country. You need to check the local regulations for the countries in which you will be using the systems. The last thing you want to do is choose a technology or product line, install it in half of your facilities, and then find out you have to use a different system in the remaining facilities because what you selected is not permitted in certain countries. You can avoid much of this problem by selecting a vendor that provides this technology on the open world market, as opposed to a vendor that does not export any of this technology. Also ensure that the security assets you purchase are appropriately configured, and legal, to export; again, this issue will be greatly alleviated if you select a vendor that routinely ships this technology to many countries around the world.

Will anything in the building construction interfere with the RF signal?

You need to determine whether the facility is built such that RF will penetrate into the necessary areas or whether you require special antennas to get coverage in certain areas. Remember that 2.4-GHz signals will penetrate standard construction easier than 5-GHz signals. A good practice is to actually do some on-site testing with both technologies to verify performance in your typical environment.

Does the facility use any other 2.4- or 5-GHz equipment, such as Bluetooth systems, cordless phones, microwaves, wireless security cameras and alarms, and so on?

If other systems are installed and actively used, this may be a reason to choose one technology over another. However, it may also just require your attention during the site survey and installation to be certain the interference is kept to a minimum. Many times this can be achieved by proper placement of APs and antennas.