This chapter does not list feature information vendor by vendor. The quantity of information would be overwhelming and the listing would quickly become outdated. Instead, this chapter aims to help you understand the features and characteristics that are available on wireless equipment. When you understand the features and their significance, you will be in a position to select the equipment that best meets your network needs.
Any New Features This Week?
Wireless equipment is evolving rapidly. Wireless hardware and software features change each week. I have attempted to describe all the significant wireless hardware and software features that were offered (by at least one equipment manufacturer) at the time I wrote this chapter in 2002. Because of rapid equipment evolution, I suggest that you supplement the information presented here with your own feature research.
This chapter contains the following major sections:
A description of the equipment selection process.
A brief explanation of the International Organization for Standardization (ISO) Open Systems Interconnection (OSI) seven-layer reference model. An understanding of this model helps you understand how various wireless features fit into your network.
A list of equipment features, arranged by OSI layer. Following each feature is an explanation of the feature.
A summary of the features that are the most desirable for wireless backbone equipment, access points (APs), customer premises equipment (CPE), wireless network cards, mesh network nodes, and amplifiers.
A discussion of compatibility issues that can cause problems when mixing wireless equipment from different vendors.
Suggestions about evaluating and receiving vendor support.
Overview of the Equipment Selection Process
Your equipment purchase can involve spending only a few hundred dollars, or it can involve spending hundreds of thousands of dollars. The more money that you plan to spend, the more important it is that you include all of the following steps in your selection process.
Reviewing Your Wireless Network Needs
Before you select your wireless equipment, take the time to review your wireless network needs:
How many wireless end users do you want to serve?
What network architectural elements do you want your wireless network to include?
Do you need only point-to-point links or will you deploy point-to-multipoint APs?
Do you need wireless backbone bandwidth?
Do you need mesh network nodes or repeaters?
What features will your wireless network need so that it can connect to your wired network?
Will you need routing or only bridging?
After you have reviewed both the wireless network features and the wired features that you need, you are ready to begin researching specific wireless equipment features.
Researching Equipment Features
Now that you know your network needs, you can begin listing wireless equipment that matches your needs. The most difficult part of the research process is not learning what features a particular brand of equipment offers. The most difficult part is learning what features are not offered or which features do not work the way you expect them to work.
If you have not worked with wireless equipment before, it can be difficult to get an accurate picture by looking only at press releases and advertising flyers. Press releases are typically loaded with attractive buzzwords that promise wireless performance and wireless benefits that are sometimes exaggerated or theoretical. Advertising flyers and spec sheets do not lie about equipment performance, but they sometimes omit information that would reveal performance shortcomings.
Evaluate equipment that offers the specific features that you need, such as distance and bandwidth capabilities, but before you decide to buy, visit a network where that particular vendor's equipment is deployed.
Visiting Deployment Sites
After you have researched equipment features, you will have one or more equipment vendors who can provide equipment that appears (at least on paper) to meet your wireless needs. It is appropriate and proper for you to ask the vendors to recommend one or two existing wireless networks that have deployed their equipment. Visit these sites and talk with the network operators who have deployed the equipment.
Your visit will allow you to learn what features work especially well and what features do not work as expected. You will learn which expectations were exceeded (the good news) and which expectations were not met (the not-so-good news). You will learn if the equipment is easy or difficult to manage. You will also learn if vendor support is poor, good, or outstanding. This is information that you cannot obtain from a spec sheet or an advertising flyer. With the benefit of this information, can make an accurate and informed decision about which equipment to purchase.
Testing Wireless Equipment in the Lab
When you have completed your site visits, there will probably be one or two vendors that you think would be good equipment providers. At this point, consider making a small equipment purchase consisting of either a pair of wireless units or one AP and one CPE unit.
Set up these units indoors and become familiar with them. Configure the units and measure their throughput in both directions. Learn to use the diagnostics.
Practice safety when you are working near wireless equipment. High amounts of microwave energy can cause damage to the human body, so minimize your exposure to this type of energy. Do not point a directional antenna at yourself or at any other nearby person. Turn the wireless equipment off any time you are not testing it. Remember: When you double the distance between yourself and a wireless antenna, you reduce the amount of radiation reaching you to one-fourth the previous level. Whenever possible, maintain as much distance as possible between yourself and a wireless antenna.
When your indoor testing is complete and you are comfortable with the units, proceed to outdoor testing.
Testing Wireless Equipment Outdoors
Testing wireless equipment outdoors allows you to test the range, throughput, and reliability of the equipment in the presence of real-world noise, interference, and weather.
For your outdoor testing, perform the following steps:
|Pick two locations that are as far apart as the maximum link distance that you expect the equipment to cover. For example, if you plan to build a wireless cell with a 4-mile (6.4 km) radius, pick an AP location that is high enough to have at least two line-of-sight (LOS) paths that are at least 4 miles long.
|Test using an AP antenna system similar to the one that you expect to use in your actual network deployment.
|Temporarily set up the CPE at first one and then the other of your two test locations.
|Test during the busiest part of the day and repeat the throughput tests that you performed indoors. It is important that you test the throughput from the CPE to the AP. This is an important test of the AP's capability to receive in the presence of noise and interference. For more details about throughput testing, see the description in Chapter 7, "Installing Outdoor Wireless Systems."
If possible, repeat your performance testing several times over a period of several days or weeks. The equipment performance should remain constant throughout the entire test period.
Your outdoor testing will not tell you how many customers the AP will handle at full load, but it will give you a good preliminary performance indication. If all your test results are good, proceed to the following purchase decision step.
Making Purchase Decisions
Your testing should bring you to the point where you are most comfortable with the performance of one or two brands of wireless equipment. You can now make your purchase decision and be fairly confident that the equipment you buy will meet your performance expectations.