The cable-test standards environment continues to be something of a moving target, especially for higher frequencies. Rich helstrom, director of marketing at Wavetek Wandel Goltermann's LAN & Test tools devision in San Diego, USA, Investigates the situation.
In today's dynamically changing network environments, the need to 'future-proof' cabling installations is becoming more critical every day. Corporate customers want to be sure that every new cabling investment can effectively handle the potential migration to higher speed protocols, so they typically are leaning toward specifying cable that exceeds today's 100 MHz practical usage limits. On the other hand, the cable-test standards environment continues to be something of a moving target, especially for higher frequencies. This dichotomy, between the need to install higher speed cabling today and the need to have it work 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 factors:
* Emerging high-speed 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 tomorrow's requirements.
Straddling the shifting standards
Even though 100 MHz is essentially the upper bound of today's adopted standards, the reality is that cable manufacturers are building products capable of speeds in the 350 MHz range and higher. Although they obviously cannot put the full potential of this higher speed cabling to immediate usage, many organisations are opting for the 'insurance value' of investing in it now to ensure room for future migration.
Ultimately, installation contractors must be able to competitively respond to customer requirements for certifying cable to higher speeds as the standards develop. In order to accomplish this, installers must be able to anticipate the test requirements for upcoming standards.
Over 60% of all cable installations are already Category 5 and, with the worldwide wiring market growing at more than 18% per year, the dominance of Cat 5 wiring is rapidly increasing. Although Category 5 wiring has been nominally rated for speeds up to 100 MHz, the testing requirements for certifying it to its full capabilities (using all four wiring pairs) have lacked complete definition. In actual practice, the fact that most existing network protocols (such as 10Base-T and 100Base-T) only use two wiring pairs at a time means that there is usually sufficient headroom to spare. However, the movement toward higher speeds, such as Gigabit Ethernet or 622 Mbps ATM, is now demanding more stringent testing levels for Cat 5 cabling installations. The Telecommunications Industry Association is currently in the process of adopting an Enhanced Category 5 standard which will include new Level 3 testing and certification to support reliable transmission of 100 MHz traffic simultaneously using all four pairs of UTP wiring. The Enhanced Cat 5 requirements will include the use of simultaneous four-pair performance tests such as PowerSum ACR, PowerSum NEXT, and PowerSum ELFEXT as well as channel return loss testing.
Basically PowerSum NEXT assesses the multiple disturber crosstalk effects of three pairs simultaneously transmitting by measuring the coupled effect on each fourth pair. PowerSum 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 wiring assembly.
In addition to Enhanced Category 5, ISO/IEC and TIA are also jointly laying the groundwork for formal definition of next generation cabling standards to provide reliable transmission speeds at greater than 100 MHz. Tentatively, these are specified as follows:
* ISO/IEC Class E (TIA Category 6) - specified to 200 MHz, using UTP and the existing RJ45 connector standard.
* ISO/IEC Class F (TIA Category 7) - specified to 600 MHz, using individually shielded wiring pairs and a new as-yet-undefined connector design.
ISO/IEC working committees are still refining draft specifications for Class E/Cat 6. It is possible that committee drafts will be available early 1999 and formal adoption could occur as early as mid 1999 for ISO Class E. The working objective is for all the new classes/categories to maintain full backward compatibility with applications that run on lower categories.
Because Categories 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 Cat 3 to Cat 5 installations. At 200 MHz, Cat 6 is essentially being defined to represent the maximum practical transmission bandwidth that is achievable using UTP wiring and RJ-45 connectors. On the other hand Cat 7, with its requirement for higher cost individually shielded wiring, may find itself competing head to head with multimode fibre on a cost/performance basis.
As with Category 5, both Cat 6 and Cat 7 will require extensive simultaneous testing of all four wiring pairs for both near-end and far-end crosstalk (PowerSum NEXT & PowerSum ELFEXT), attenuation to noise (PowerSum ACR) and channel return loss characteristics. From the perspective of a cable installation contractor, this shifting standards picture definitely will dictate a need to quickly invest in both the equipment and training needed to routinely conduct higher level tests. In addition, it means that they 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 in Cat 7.
Planning for future tester migrations
For cable installers, the continued migration to higher speed cabling offers an attractive opportunity for increasing their value-added but also means extensive investment in both capital equipment and staff training. Installation contractors can't afford to wait too long to invest in new capabilities nor can they risk jumping in too quickly. Installers need to carefully plan their investment strategies over the next few years, in order to stay on the leading edge, but avoid over-spending or ending up with obsolete test equipment. According to Universal Cabling's Ron DuBeau, "A key issue for us is ensuring that the test vendors will participate with us in any required upgrades. If EIA and TIA change the upcoming standards, we need to know that we won't have to bear the burden of the whole cost."
The bottom line for both cabling installation contractors and their customers is that the world will continue to change. Recently, we have seen the widespread adoption of the Enhanced Cat 5 testing standards along with the further refinement of the Cat 6/ISO E standards. Throughout all of this change, contractors will continue to install new cabling while customers will continue to press it toward its physical limits. At 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.
The LT 8155 is Wavetek's new, portable cable tester for LANs, which meets the latest technical requirements for measurements on Category 5 cables and offers a broad palette of functions. Installers and network administrators can use the LT 8155 to install and certify networks for bit rates up to 155 Mbps with considerable cost savings, claims the company. Features such as an autotest takes less than 10 s, a built-in tone generator and an optional full-duplex talkset are also featured.
According to the company, the LT 8155 was developed especially for cables that push conventional Category 5 cable testers to their limits. The LT 8155 also offers high level III measurement accuracy, plus measurement of the NEXT reserve, return loss on both ends, ELFEXT, power sum NEXT and ACR up to 155 MHz. The tester has internal storage space for up to 1500 test results. It includes built-in project management and simplifies error analysis with detailed graphics.
Tests on challenging open architectures are simplified: The LT 8155 allows connection of up to four terminals and can handle fibre cables. Because the LT 8155 can be used to certify Fast Ethernet, 155 Mbps ATM and Gigabit Ethernet installations, the tester will stay viable for a long time to come says WWG. In conjunction with FIBERKIT+, the LT 8155 can be used to measure attenuation on diverse fibres. Adapters are used to access multimode and single-mode fibres. Functions such as automatic wavelength detection and switching is a further innovation.
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