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Wireless Networking Handbook
(Publisher: Macmillan Computer Publishing)
Author(s): Jim Geier
ISBN: 156205631x
Publication Date: 09/01/96

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Testing the Installation

In the software world, testing is extremely important—countless problems have resulted from defects in software. You might have heard, for example, about the farmer in a remote area of Nebraska who one day received thousands of the same copy of Time magazine? Apparently, the publisher’s label printing software had a defect that made it spend hours printing the same address. Defects in networks might not cause similar incidents, but improper configurations and unforeseen propagation impairments can easily discontinue the network’s operation. This is especially serious in hospitals where a doctor’s or rescue person’s access to information can create a life-or-death situation.

Concepts of Testing

Several definitions for testing exist. Some people say that testing is for checking if the system offers proper functionality, and others say the reason for testing is to find conditions that make the system fail. Actually, testing is a combination of the two: it ensures the network behaves as expected and that no serious defects exist. Figure 10.5 illustrates the elements of network testing.

Test Cases

A test case represents an action you perform and its expected result. For example, one test case might determine whether access to a database meets performance requirements. The action would be to run a particular query, and the expected result would be the time it takes for the query to return the corresponding data.

How do you write test cases? First, be sure to review the later sections on performing unit, integration, system, and acceptance testing before writing test cases. Then, referring to the network requirements and design defined earlier in the project, describe the tests necessary to ensure a network that behaves adequately. The following are attributes of a good test case:

  Has a good chance of uncovering a defect
  Can be performed easily
  The expected result is verifiable


Figure 10.5  The elements of network testing.

Test Execution

With a complete set of test cases, you’re ready to run the tests. As you’ll see later, testing takes place throughout the installation phase. You might have noticed that building contractors must carefully inspect the foundation before building the structure on top; otherwise, the building itself could hide support structure defects that could later cause a disaster. Network testing is similar; you should fully test the radio connectivity and cabling before installing and testing their interaction with the network operating system and application.

Test Results

The outcome of performing test cases is test results. Of course, you hope everything checks out okay. Poor results indicate the need for rework, meaning a design modification is necessary and components need to be reinstalled or reconfigured. This will take time to complete, possibly extending the project. Recording test results for observation later when supporting the network is a good idea. Test results offer baseline measurements support staff can use to aid in troubleshooting future problems.

Evaluation Comments

After obtaining the test results related to the portion of the network under testing, compare them to the expected values identified in the test case. The evaluation comments should explain any differences and, if necessary, recommend corrective action.

Corrective Actions

Figure 10.6 shows an example of a form you can use to document test activities. The data provides baseline information for later testing. When problems arise during the network’s operational life, you can run tests again and compare them to the ones run during installation, which can also help pinpoint problems.

The best method of testing the network installation is to follow a bottoms-up approach by performing the following types of tests:

1.  Unit testing
2.  Integration testing
3.  System testing
4.  Acceptance testing


Figure 10.6  A sample form for documenting test activities.

Performing Unit Testing

Unit testing verifies the proper internal operation or configuration of individual network components, such as network interface cards, servers, cables, printers, and so forth. You should unit test each component—before trying to make them work with other parts of the system—to ensure the components themselves are not defective. Knowing that individual parts work to make future troubleshooting problems easier. Figure 10.7 illustrates the concept of unit testing.


Figure 10.7  Unit testing makes future troubleshooting easier.

Ideally, you would want to fully test all possible functions and configurations of each unit; however, that’s usually not feasible. The following sections offer examples of unit tests you should perform.

Testing Individual Components

Be sure to test the operation of each component, such as printers, servers, and access points, before integrating them with other components. Most components have built-in self-tests that run whenever you turn the device on, or they have test utilities that you can run manually. Therefore, you usually won’t need to develop specialized test cases for most individual units. Proxim’s RangeLAN2, for example, comes with a utility called RL2SETUP which verifies whether you’ve chosen an I/O address, IRQ, or memory window that may conflict with other hardware.

Testing Category 5 Cable Installations

Cable problems rank high as causes of networking troubles. Mechanical elements, such as cabling, connectors, and wall plates, tend to fail more often than active electronic devices such as network adapters and switches. Approximately 85 percent of cable problems arise from the installation; therefore, be sure to fully test cable installations. Cable faults result from improper splices, improper connector attachments, lack of termination, and corrosion.

The good news is cable problems are relatively easy to find, especially if you utilize an effective cable tester conforming to TIA’s Technical Service Bulletin (TSB) 67, published by the Link Performance Task Group of the Telecommunications Industry Association (TIA). This TSB is not a standard, but it does describe how to test Category 5 twisted-pair cable. You should definitely consider TSB-67 when selecting a cable tester.

TSB 67 addresses two link configuration models: Channel Link and Basic Link. The Channel Link consists of the patch cords that connect the access points to the horizontal wiring, and the horizontal wiring itself can span a total of 100 meters. Channel Link testing covers a range that verifies wiring connections up to the user’s interface. The Basic Link only includes the horizontal wiring and two 2-meter tester equipment cords and can be 90 meters long. Installation crews commonly perform Basic Link testing after laying the cabling.


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