Keeping cable testing ahead of the curve

In today`s dynamically changing network environments, the need to futureproof cabling installations is becoming more critical every day. Corporate customers want to be sure that every new cabling investment they make can handle the potential migration to higher-speed protocols. So they typically specify cable that exceeds today`s 100-megahertz practical usage limits. At the same time, cable-test standards continue to be something of a moving target, especially for higher-frequency transmission.

Oct 1st, 1998
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Keeping cable testing ahead of the curve

In the face of constantly changing standards, does your cable tester measure up?

Rich Helstrom

In today`s dynamically changing network environments, the need to futureproof cabling installations is becoming more critical every day. Corporate customers want to be sure that every new cabling investment they make can handle the potential migration to higher-speed protocols. So they typically specify cable that exceeds today`s 100-megahertz practical usage limits. At the same time, cable-test standards continue to be something of a moving target, especially for higher-frequency transmission.

This need to install higher-performance cabling today while ensuring it works with tomorrow`s yet-to-be-defined standards presents most cable-installation contractors with a difficult challenge. To survive and thrive in this dynamic environment, cable installers must thoroughly understand and balance the following:

- emerging standards and the cable tests that they will require

- optimal field-test methods to get the most out of their equipment

- the changing capabilities of today`s cable-test equipment

- upgrade and migration strategies to meet future requirements

Straddling shifting standards

Even though the upper bound of today`s standards is 100 MHz, many cable manufacturers are making products capable of 350-MHz frequencies--some even higher. Although they cannot put the full potential of this higher-performance cabling to use immediately, many organizations are investing in it now to ensure room for future migration. Ultimately, cable-installation contractors must be able to competitively respond to customer requirements for certifying cable to higher frequencies as the standards develop. Installers therefore must be able to anticipate the test requirements for upcoming standards.

More than 60% of all cable installations are already Category 5, and with the cabling market growing at more than 18% per year worldwide, the dominance of Category 5 cabling is rapidly increasing. Although Category 5 cabling has been nominally rated for frequencies to 100 MHz, the testing requirements for certifying it to its full capabilities (using all four cabling pairs) have not been defined. Since most existing network protocols such as 10Base-T and 100Base-T use only two cable pairs at a time, there is usually sufficient headroom to spare. But, the movement toward higher-speed protocols such as Gigabit Ethernet and 622-megabit-per-second Asynchronous Transfer Mode demands more-stringent testing for Category 5 cabling installations.

The Telecommunications Industry Association and the Electronic Industries Alliance (tia/eia--Arlington, VA) are currently developing a standard for an Enhanced Category 5 (5E), which will include new Level 2E testing and certification to support reliable transmission of 100-MHz signals simultaneously using all four pairs in an unshielded twisted-pair (utp) cable. The Category 5E requirements will include the use of simultaneous 4-pair performance tests such as power-sum attenuation-to-crosstalk ratio (acr), power-sum near-end crosstalk (next), and power-sum equal-level far-end crosstalk (elfext), as well as channel return-loss testing.

Basically, power-sum next assesses the multiple-disturber crosstalk effects of three pairs simultaneously transmitting by measuring the coupled effect on each fourth pair. Power-sum acr measures the difference between attenuation on a particular pair and the power-sum next results of that particular pair measured with the other three transmitting pairs. Power-sum elfext performs a similar test to assess the far-end multiple-disturber crosstalk effects on a near-end received signal. Channel return loss measures the reflected signal caused by impedance mismatches along the entire structured cabling assembly.

In addition to the proposed Category 5E standard, the International Organization for Standardization and International Electrotechnical Commission (iso/iec--Geneva) and the tia are jointly laying the groundwork for formal definition of next-generation cabling standards to provide reliable transmission at frequencies greater than 100 MHz. Tentatively, these are specified as follows:

- iso/iec Class E (tia Category 6)--specified to 200 MHz using utp cable and the existing RJ-45-style connector

- iso/iec Class F (tia Category 7)--specified to 600 MHz using individually shielded cable pairs and an as-yet-undefined connector design

While Category 5E is already in the process of formal adoption, iso/iec working committees are still refining the initial draft specifications for Class E/Category 6 and Class F/Category 7. Formal adoption could occur as early as 1999. The objective is for all the new classes and categories to maintain full backward compatibility with applications that run on lower categories.

Because Category 6 and 7 cabling will use entirely different media types, it is unlikely that customers will simply skip over Category 6 in the same way that the industry went immediately from Category 3 to Category 5 installations. At 200 MHz, Category 6 is being defined to represent the maximum practical transmission bandwidth achievable using utp cabling and RJ-45-type connectors. On the other hand, Category 7, with its requirement for more-expensive individually shielded cabling, may find itself competing head-to-head with multimode fiber on a cost/performance basis.

As with Category 5, both Category 6 and 7 will require extensive simultaneous testing of all four cable pairs for power-sum next, power-sum elfext, power-sum acr, and channel return-loss characteristics. From the perspective of a cable- installation contractor, this shifting standards picture will dictate a need to eventually invest in the equipment and training needed to routinely conduct higher-level tests. In addition, contractors will need to carefully plan their equipment investments to include built-in flexibility for migrating to the as-yet-undefined connector form factors that will be used with Category 7.

Having the appropriate test capabilities to certify cabling to the customer`s specified bandwidth is the heart of any cable-testing investment. However, there is much more that must be considered for contractors to get maximum productivity out of their equipment investment and field staff. Key issues include

- procedures for faster testing

- storing tests, managing data, and generating reports

- protecting the tester from damage

Procedures for faster testing

Installers should be trained on the key disciplines required for efficient testing. For instance, field testing must integrate with a myriad of other activities, such as determining and tracking cable identifiers (often using customer-defined nomenclature); smoothly integrating the cable-labeling process; supporting rapid sequential testing of bundled cables; and easy movement from each location to the next. However, when a problem is encountered, the installer must be able to immediately "drill down" with more analytic testing to find and correct any anomalies.

To support the field installer, today`s local area network (lan) testers must deliver a balance of quick and easy auto-testing along with in-depth analysis capabilities. For instance, setting up the tester to automatically increment each cable identifier in sequence can greatly speed up the process of conducting a series of sequential tests. Instead of physically typing in the name of the cable and entering a command to store the results after each test, the installer can simply move from test to test, while automatically storing the results sequentially.

Testers with built-in earphone/microphone headsets also speed up field work by enabling technicians at opposite ends of the cable to communicate without the hassle or expense of separate walkie-talkies. By automatically using a pair of good cables to establish communications, these testers enable the voice link whenever testing is not in progress. In addition, testers with built-in tone generation can speed testing by automatically generating required test tones and continuing to broadcast until either the near end is detected or a specified "time-out" period has expired. This type of tester is especially useful for identifying jacks that have been mislabeled or not labeled at all.

"Tester ease-of-use features, such as quick-testing capability, are very important to boosting productivity in the field--especially when the installer has to keep moving from outlet to outlet in a large installation," says Ron DuBeau, a partner in Universal Cabling Systems Inc. (West Palm Beach, FL). "However, we also feel it`s very important to train all of our installers to understand and be able to use all of the features in the tester. For the most part, we want them constantly moving through routine tests at the full speed of the auto-test capabilities, but when necessary they`ve got to be trained to access and effectively use the lan tester`s full feature set. To us, the lan tester is a critical investment, and we can`t afford to have any of its capabilities go to waste because of a lack of knowledge on the part of our staff."

Test reporting

Although industry-wide standards for reporting formats have not yet been established, many customers are requiring detailed backup data in addition to summary certification reports. In the past, many customers only required pass/fail data; however, the trend is toward archiving complete sets of test results. As corporate management information systems (mis) departments become more sophisticated with their in-house test capabilities, having a full database of certification detail will help support their future moves, adds, and changes (macs) by giving them complete baseline data against which to compare future tests. In addition to assisting the customer, the archiving of an audit trail in the form of a detailed record of all the tests performed is essential protection for contractors to back up their certifications.

Given the extremely long warranty periods currently applied to cabling (some as long as 25 years), it is vital that each contractor retain meticulous records of all test data. While cabling rarely deteriorates by itself over time, there is always the potential for change-inflicted damage to some part of the structured cabling system. Without detailed records of the original test results, contractors have no firm basis from which to determine the legitimacy of subsequent warranty claims. In these instances, it also helps if both the installer and the customer`s mis personnel have similar equipment. When the customer is able to conduct exactly the same tests that were used by the contractor, it quickly eliminates tester variability as the source of disagreement.

For larger or rapidly growing installation companies with a mix of skills and knowledge levels, it is often useful to be able to deploy a variety of tester configurations with capabilities to match the technicians` skills and duties. For instance, the ability of the tester to locally store many days` worth of tests is becoming increasingly important, especially for installers who may spend long periods on the road without returning to their headquarters. But, it may not be practical or desirable to outfit all the staff with high-end testers that can store 1500 sets of tests, when in practice the entry-level staff may only conduct 150 tests before reporting in and uploading the results. Another function that many contractors find useful is the capability to undelete the last action. No matter what the skill level of the operator, there is always the occasional risk of erroneously deleting test data.

One emerging issue regarding test storage is the potential use of laptop computers for uploading and managing data in the field. Obviously, laptops give installers more flexibility for storing extensive test data that outstrips the internal capacity of the tester. A laptop also can provide quick options for generating customer reports in the field.

Over the past year, some of our cabling installers have successfully used laptops directly integrated into the test environment. On the other hand, many cabling installers do not feel that laptops in the field are the best way to go. For instance, "We`re concerned about putting the responsibility on the installer to manage another expensive piece of field equipment," says Universal Cabling`s DuBeau. "We`d rather see a continuation of the trend toward testers that provide more internal storage and communications options. The more the tester can help minimize the overall physical load on the installer, the more productive we can be in the field. As a matter of fact, we`d be interested to see an option for testers with a built-in 3.5-inch diskette drive to download a quick copy of the test results in the field. This would allow for more internal storage and to give the customer access to review the test results on-site."

When working in "live" environments, such as testing operational cabling or making macs, the contract installer or in-house mis person must also take special precautions to avoid damage to the tester. An RJ-45 connection for the lan can look and feel exactly the same as one used for any of a number of different functions, such as telephone or digital private branch exchange services. However, the pin-outs and voltage risks can be significantly different. Compounding the problem is the possibility that outlets may have been mislabeled in the original installation or that labels may have been lost or changed during previous mac activity. The risk of erroneously applying 48 volts (96V during a ringing cycle) into the lan tester can do immediate damage, impacting both the contractor`s capital investment and loss of staff time until the tester can be replaced. In addition to carefully training their staff to avoid making erroneous connections, contractors should look for built-in protective features or automatic warning messages on the display to allow disconnection before permanent damage occurs.

Planning for future migrations

For installers, the continued migration to higher-performance cabling offers an attractive opportunity but also requires extensive investment in both capital equipment and staff training. They cannot afford to wait too long to invest in new equipment or risk jumping in too quickly. Installers need to carefully plan their investment strategies over the next few years to be at the leading edge but avoid overspending or ending up with obsolete test equipment. DuBeau cites another concern: "A key issue for us is ensuring that the test vendors participate with us in any required upgrades. If the tia/eia changes the upcoming standards, we need to know that we won`t have to bear the burden of the whole cost."

The industry will continue to change for both cabling installation contractors and their customers. Throughout this change, contractors will continue to install new cabling while customers will continue to press it toward its physical limits. Each step of the way, the cable-testing industry will have to provide cost-effective and extensible solutions that always stay abreast of users` current needs while anticipating and planning for future requirements.

Click here to enlarge image

Testers with built-in headsets enable technicians at remote ends of the cable under test to communicate easily without separate walkie-talkies.

Rich Helstrom is director of marketing at Wavetek Corp. (San Diego, CA).

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