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| Taking Technology to the Next LEVEL
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| Before the existing Category 5 standard was signed in late 1995, billions of feet of cable had been installed based on the hint of a standard known as TSB-36. To make a complete cabling system operable TSB-40, and then -40A, were used to cover the connectivity issues for the installation. Much later came the development of the final piece of the puzzle called TSB-67, which established guidelines for the installed performance of the system and how it should be tested and verified in the field. These "NEAR" standards were brought together in late 1995 with the signing of the ANSI/TIA/EIA-568-A revised standard. We still do not have standards for patch cable assemblies or for how to test and measure system performance reliably. Nor is the definition of the "Link" or "Channel" completely clear. If a company has installations across country boundaries, what standards should they adopt for the structured cabling system infrastructure? They can pick from an ever-increasing list, not limited to just the ANSI/TIA/EIA-568-A, -569-A, -607 and -606 series, but including ISO 11801 and CENELEC 50173 as well. They could also choose from among the emerging standards for UTP, STP and ScTP systems being developed by IEC, NEMA, IECA, DIN and on and on. Today there really is no one single overriding standard to turn to that covers everything for a true interoperability guarantee when installing a structured cabling infrastructure.
Establishing Performance Requirements
By late 1995, there were over 37 manufacturers of Category 5 cable products certified by the two main independent testing labs in the US. Of these, approximately 21 were North American-based companies. About 15 of these companies were also selling cables with claims of "Enhanced" Cat 5, or "Better" then Cat 5, or "Exceeds" Cat 5 performance. Most warranted these based on a "margin" of performance to the Cat 5 specification. The problem was this margin was never of the same magnitude or the same parameter. The claims ranged from a low of 3 dB to a high of 16 dB better than Cat 5 in either NEXT or ACR, or some times both. These claims were for "Average", or "Worst Case" or "Worst Case Average" or "90% Average" or "90% Worst Case." The cables were either new designs or just tighter test controls. It seemed that for some manufacturers if they could improve even a single parameter it became a revolutionary breakthrough design. A truly new design should effect an overall increase in true usable bandwidth.
On top of these higher-rated designs were the construction changes caused by the FEP shortage during 1994 and 1995, which severely impacted the availability of plenum cable. Manufacturers were using non-FEP materials on a single pair or two pairs and mixing these with the FEP-insulated pairs under new jacket materials and designs to maintain market demand volume, not to enhance cable performance. As the FEP situation has eased, these mixed-material designs are being maintained because they are cheaper to manufacture as these products are being commoditized. This mixed-material design causes electrical performance conditions not originally thought to be potential sources of problems during the development of TSB-36 or TIA-568-A. The test parameter for delay skew was added this April 1997, and requires a propagation delay skew of less than 45 ns for Category 5 cables. Is this now Cat 5.1?? What about cables manufactured before this date? Will they work on all current and future applications requiring four-pair
technologies?
In order to provide our customers and our supplier-partners with a clearly defined choice of workable and eventually interoperable solutions, the Anixter Levels Purchasing Specification for UTP, which has been in place since mid-1988, was completely rewritten to incorporate the performance issues of 1997 (Anixter Levels '97SM). The following information is a result of the cable and link testing and technical information gathering that was completed in order to establish the foundation for this document. It is being offered here as background data to enable our customers and the structured cabling community to better understand the factors that caused us to open the book on Level 5, 6 and 7.
There are three Levels of performance that make up the division of the Category 5 cable solutions that we now recommend to our customers. (Contact Anixter for information on the performance specifications.) These requirements are based on a variety of standards, not just a single document. The requirement for NEXT is the power sum calculation per ASTM and is mandatory for all three Levels. All of the new increases in usable bandwidth of UTP will need to rely on using all four pairs as signal pairs. The Category 5 standard is only a two-pair specification and never was intended to supply signaling on more that two pairs (see the delay skew fiasco above). The extended frequency testing and performance requirements are added to assure stable electrical properties and manufacturing quality of all cables inventoried and supplied by Anixter. Some results of the extended frequency testing for both cables and links are presented in the following section. The ultimate goal is to establish the link and channel requirem
ents for all three Levels and also develop the purchasing specification for Level 6 and 7 connectivity products. The cable portion was the most critical issue because it is the most substantial component decision that is made in a system. The product development for cables has matured to the point that the parameters required for good performance are readily understood and measurable. We start with the cable and everything else builds from it.
Verifying to the Performance Requirements
From 1988 to 1994, when our original purchasing specification was in place, all product in our inventory was routinely subjected to random electrical verification testing by contracting through independent testing facilities. If any product was found non-compliant, the entire inventory of that product was returned. With the increasing requirement to provide our customers with complete infrastructure solutions, it became clear that we would have to be able to test and simulate actual applications running on actual structured cabling solutions. We also wanted to be able to provide our structured cabling systems engineers with guidelines as to the performance characteristics of the cable and components we are offering as systems solutions.
In early 1995, the $2 million Anixter Interoperability Lab was added to the Technology and Training facility in Mount Prospect, Ill. This lab afforded our network systems engineers with the capability of trying out solutions for their customers from permanently installed components of all supported suppliers products. This represented all network applications from Ethernet (standard and switched), Token Ring, and early ATM and remote access switching. All possible combinations of hubs, routers, switches and NICs were present and available to any port in the lab through a structured cabling system containing UTP, STP and fiber backbones to all devices, along with all major LAN manager software packages and LAN administrator software. Later that year Anixter invested another $2 million in the lab, which doubled its size and added full remote access capabilities with internalized Frame Relay and ATM clouds in the static lab and inclusion of all seven supported ATM switches in the Dynamic lab.
Anixter's Dynamic Lab offers facilities for testing interoperability for all network infrastructure hardware.
With an application laboratory of this magnitude it was decided to install a structured cabling test facility internal to the lab. We permanently installed cable products of all designs that were sold as Category 5 from 1991 to 1997, e.g., plenum, non-plenum, standard Cat 5, enhanced Cat 5, also STP and ScTP. In total, there are more than 110 90-meter cable runs in the lab today. We also installed in cabinets all connectors, patch panels and blocks available through our inventory in the same period. To facilitate rapid test set-ups for sample verification on 100-meter lengths, a series of interducts and pulleys was installed overhead; new cables can be pulled in for testing in less than two minutes. Patch panels were installed to patch any cable, connector, block or second patch panel to any other, and to any active component or components in the lab or the entire building. We are currently evaluating various BERT devices for future expansion.
Anixter's Structured Cabling Lab
The primary purpose of the Anixter Structured Cabling Lab is to assure our customers that solutions and products provided by us will work as intended and will work with the active components in their overall enterprise solution. A secondary purpose is to constantly monitor the Anixter Levels '97 Purchasing Specification through random testing of actual product from inventory. We are also working closely with our partner suppliers on the next generation of products, and making the lab available as a beta site for new networking and structured cabling concepts and equipment. In addition, we are working with the TIA/EIA 41.8 group, along with the NEMA and ICEA enhanced performance cable committees, to assist with their discussions. As a charter principal member of The ATM Forum and ENR, we are constantly evaluating components relative to those requirements.
Contact Anixter for information on the components and test equipment available in the Structured Cabling Lab. Samples of the actual tests that have been performed over the past year to establish our inventories of Levels-compliant cables are also available on request. These are all measurements above 100 MHz, and show anomalies in cable performance that were all traceable back to defects in manufacturing processes or cable design.
Link and Channel Defined
The Link and Channel parameters have just been added to the Levels specification and will be followed with the specifications for Level 6 and 7 connectors. The basic Level 6 Link and Channel requirement is the same as that for the Category 5 under TSB-67, except the values for NEXT are power sum not simple worst pair. The patch cord requirements are the same with the tighter NEXT measurements. The Level 7 requirement is much harder to meet as the attenuation of the patch cables must be lower than either Level 5 or 6 at no more than 10 percent greater than the Level 7 cable requirement. Graphs are available of the actual test results of various Levels of components installed in Links and how they interact with each other in ACR plots. The testing was made at frequencies up to and over 300 MHz to show the effect of cable and connectors out to where the ACR = 0.
Summary
The Levels specification is not intended to be a standard but only a document provided to assure our customers that the performance they expect is what they get. In some cases the parameters are not easily met, and not all manufacturers are willing to expend the costs to modify manufacturing and test equipment to comply. In those cases, we would not support those products. As the standards are changed and adopted, and new test and design parameters are added to the structured cabling solutions -- such as EMC, FEXT, ELFEXT, LCL and NEXTrms -- then we will change the purchasing specification to address these requirements.
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