As cable testing standards evolve, installers must keep up with the changes or face extinction.
The demand for faster, more powerful local area networks (LANs) has led to the design of networks that handle more and larger transmissions -- at faster bitrates. As these networks continue to evolve, so do cable standards and the rules governing how cables are tested. Cable installers must keep abreast of these changes to continue building systems that meet new customer demands. Before looking at these changes, however, installers must understand the importance of two factors critical to LAN cable testing:
Transmission rate
. This is the issue most of us think about when dealing with LAN testing and the one we will pay the most attention to in this article. How quickly can we get signals from Point A to Point B? Will the cable, connectors, and associated devices permit this transfer speed, or will they distort the signal? These are critical issues.
Network management
. Can the network handle the traffic levels? Consider a network running at 100 Mb/s, with three nodes (or, computer stations) connected to it, each transmitting 30 Mb/s. This should work fine. But what if you connect another 10 nodes to the same network? Total network traffic can become a serious issue.
Organizations
. Several industry organizations, including the Telecommunications Industry Association (TIA), the Electronics Industries Alliance (EIA), the American National Standards Institute (ANSI), the International Organization for Standardization (ISO), and the International Electrotechnical Commission (IEC) have put specific standards in place that:
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Promote consistent cabling design and installation practices.
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Encourage conformance to physical and transmission line requirements.
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Act as a basis for examining a proposed system expansion and other changes.
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Serve as a consistent structure for uniform documentation of cabling installations.
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Increase interoperability across mixed-vendor environments.
The evolution of ANSI/TIA/EIA and ISO/IEC standards to encompass higher performance cabling links has also driven an expansion of test requirements to ensure reliable installation compliance at each level. The Table above displays the various test suite components, such as line map, link length, attenuation, impedance, crosstalk, and ELFEXT, and it relates each test to the applicable TIA categories and ISO classes.
Test requirements
Cat. 3 cables are mostly used for telephone and low-speed data applications such as 10BASE-T.
Cat. 4 cables have been omitted from the comparison table because they have essentially disappeared and been replaced by Cat. 5 cables, which have become the cable medium of choice for horizontal cabling to the desktop.
Cat. 5 currently supports 100 Mb/s (fast Ethernet) and 155 Mb/s asynchronous transfer mode (ATM). It is also the goal of the IEEE 802.3ab committee to rate Gigabit Ethernet (GBE) at 1000 Mb/s and make it backward-compatible to standard Cat. 5 cabling. Running GBE over Cat. 5 is still considered problematic, but if it is proven feasible, the largest installed base of cable infrastructure would immediately gain about 10 times the bandwidth capability over existing fast Ethernet.
Cat. 5e is the recommended cable type for copper GBE installations. It is an interim solution that uses the same frequency sweep to 100 MHz as standard Cat. 5 cable. It does, however, provide somewhat better pair-to-pair performance and improved return loss, near-end crosstalk (NEXT), and equal level far-end crosstalk (ELFEXT). From a test parameter standpoint, Cat. 5e and Level II-E accuracy essentially push each measurement category up by 3 dB over existing Cat. 5 requirements.
Cat. 6 cables (or Class E) are intended to offer significant improvements in transmission capabilities with a frequency capability as high as 200 MHz. The adoption of Cat. 6 and Level III is also targeted to harmonize TIA Cat. 6 with ISO Class E cabling. Field test equipment for Cat. 6/Class E will be required to sweep to 250 MHz (to cover any measurements in close proximity to the 200 MHz benchmark) and test to a new Level III accuracy. Level III accuracy will incorporate all of the existing tests used in TSB95 at the Cat. 5e level. However, the movement from 100 MHz to 200 MHz traffic levels (250 MHz for the test suite) requires a significant improvement (by as much as 10 dB) in each of the critical RF parameters that characterize the test device's accuracy. This is spawning a whole new generation of field testers to meet Level III requirements.
It's important to realize there is still no approved Cat. 6 standard for the industry. Companies have been selling Cat. 6 products made to various draft standards for quite some time, but there is no approved standard at this time. You should make your customers aware of it when they request Cat. 6 cabling.
Future cabling standards
. The future definition and adoption of Cat. 7/Class F cabling standards is intended to push effective transmission speeds into the 600 MHz range. Manufacturers must increase the capabilities of unshielded cabling and the RJ-45 connector configuration to achieve this objective. Most industry participants have accepted that the most likely candidate for cabling will consist of individual shielded wire pairs, with an overall shield around all four pairs. Existing cabling such as the PIMF used in some European countries can potentially provide positive ACR values at 600 MHz. However, the high attenuation characteristics result in a relatively weak signal. In addition, the use of shielded cabling and the need for an entirely new connector design are likely to make the installation and certification of Cat. 7/Class F cabling significantly more expensive than other alternatives.
Evolving with the standards
. For installation companies entering the LAN market, a standards-based migration path (that is, installing Cat. 5 systems to gain competency, then moving to Cat. 5e, and then onward) allows them to equip their initial teams with entry-level devices and then add higher-end systems as they grow, without the headaches and expense of wholesale retraining programs.
For the large installer, the availability of several price/performance levels and support for ongoing upgrades enables them to efficiently equip and deploy more installer teams with targeted capabilities, while effectively managing their overall equipment investments. In addition, with cable installers and their customers using equipment from a common family of devices and staying abreast of changing standards, activities such as over-the-phone troubleshooting become much easier, saving both parties significant time and money in the process.
Because the need for higher performance continues to push the evolution of cabling standards and testing/certification requirements, it is imperative that professional installation companies maintain an awareness of the current state of all standards. In this environment of changing standards, professional installers must take advantage of the smooth migration paths offered by front-tier test equipment manufacturers.
