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Article 08

 

Levels - The New Standard


"When all is said and done . . . more is said than done". This old adage is particularly accurate in describing what's been happening . . . or not happening . . . in filling in gaps in the existing CAT 5 standard and in developing new standards which go beyond CAT 5. For the past 18 months or so, it seemed that every well-informed article or update on standards reported that the standards bodies in the U.S. were either "discussing," "meeting," or "studying" what to do about these matters. Finally an industry leader has stepped forward and real action has been taken.

Anixter has announced its new Levels '97 Program. Anixter's Levels rating system has been introduced as a purchasing specification guide to assure their customers receive quality, and high performance cable. However, it's a safe bet that the Anixter initiative will provide benefits well beyond their direct customers.

Anixter Inc. has led the establishment of cabling standards and specifications for nearly a decade. Along with other key members of the standards bodies, Anixter monitors technological progress and revises standards and specifications to stay current with and anticipate technology advances.

In 1988, years before the 568 standard was established, cable consisted primarily of twisted pair for voice and proprietary coaxial for data. Distinguishing one copper cable from another was difficult, if not impossible, so most people believed that all cable was the same. However, twisted-pair cable construction and electrical performance varied widely among cable manufacturers, and no uniform standard of measurement existed to compare one brand of cable to another.

In 1989, Anixter began a dialog with customers about what seemed to be indiscernible differences in communications cabling construction.

The Anixter engineers, concerned that vendor hype would distort the facts, developed and published a "Cable Performance Levels" purchasing specification for communications cables that emphatically stated that all cables are NOT created equal. The Levels specification was their attempt to create some measurement of electrical uniformity and performance assurance in the cable manufacturing process. Three years later EIA/TIA published the cabling standard that set the baseline for interoperability in structured cabling and provided a consistent platform for networking devices.

In 1993, ANSI ratified TP-PMD (twisted pair-physical media dependent) for FDDI over Category 5 UTP. Shortly after that, EIA/TIA signed the "568" standard document, followed immediately by TSB-36, which adopted in total the "Levels" requirements set forth earlier by the Anixter Levels Program - although EIA/TIA defined these levels as "categories." The Anixter engineers then worked with Underwriters Laboratories, Inc. to create the UL LEVEL testing and follow-up program, which assured end-users that the manufacture of cables would fully meet these levels/categories programs, and would give them an independent yardstick for cable performance. In addition to UL, the National Electrical Manufacturers Association (NEMA) accepted the levels defined in this program.

The industry was off and running with a new set of standards that most believed would support long-range end user needs. That belief would prove to be short-sighted.

The seven years since these original Levels were defined have seen America being rewired, information transmission technologies advancing and standards ratified. Current applications such as intranet technology, three-dimensional imaging, multimedia programs, video to the desktop, computer-aided design and broadband video are driving the need for speed and for greater bandwidth.

It wasn't until the birth and availability of affordable 100BASE-T in 1996 that institutions and organizations saw a reason to enable 100 Mbps desktops, and then largely because it was an inexpensive and well-understood insurance policy. For a little extra money, whether turned on or left dormant, dual 10/100 Mbps Ethernet network interface cards became a "no-brainer" for network managers. Fiber optics and FDDI remained in the campus backbone, and became the server superhighways and intercloset infrastructures.

In five short years (since Level 5 was introduced), the physical layer transport of the most future-thinking planners has become "maxed out" in terms of the high-speed networking options. Somebody really screwed up. In response to todays critics of standards for faster speeds and more bandwidth, you don't have to look back very far to see what changes may be coming.

This past year the ATM Forum put its seal of approval on 155 Mbps ATM to run on existing Category 5 systems, and the first interface products have just recently started to appear on the market. You better be asking what applications will require more than 100 or 155 Mbps at the desktop. Will my Category "X" cabling system have enough additional "headroom" or TRUE electrical bandwidth to provide error-free transmission when I do need the extra throughput?

Network Managers cannot afford downtime. According to a study commissioned by LeCroy, a high-end test and measurements equipment manufacturer, failures at the physical layer (structured cabling) account for an average loss of $250,000 per year per 100 users. Couple this with the fact that the physical layer represents only about 10-percent of the overall network installation costs, when including the computers, software, structured cabling and support costs, and you can see a big reason to be concerned.

All high-speed standards need to conform to SNR (Signal-to-Noise Ratios) and maximum noise thresholds. But pair skew and propagation delay characteristics are important supplemental requirements for 100BASE-T, 100BASE-VG and for ATM above 100MHz. Pair skew applies to technologies using multiple pairs for signaling. In essence, signals are divided between pairs and must be reassembled at the receiving end. If they arrive at different times, skewing of the signal occurs, resulting in transmission errors. Propagation delay, the time it takes for the signal to travel to the receiver, is a factor of the efficiency of the cable in moving the signal relative to the theoretical speed of electricity (light). Also known as the velocity of propagation, it is expressed as the percent of the speed of light represented by the cable's speed.


Network electronics manufacturers deal with electrical loss across cable distances by incorporating equalizers into their receivers. These equalizers attempt to amplify the received signal based on what they assume happened through attenuation or the electrical loss during transmission through the channel. This same received signal must also be identified within the noise picked up during its transmission and receipt, and in most cases a little bit of the noise is also reamplified. If this results in an incorrect representation of the original signal it is called a "bit error". Bit errors often lead to garbled information and/or retransmissions of the data.

As in the case of 155 Mbps ATM running on Cat 5 cable, anomalies can occur above the Cat 5 maximum signal frequency (in excess of 100 MHz and as far out as 200 MHz) that when seen by the equalizer are amplified as if they were part of the signal. This results in higher than acceptable bit errors and therefore corruption of the information. No additional headroom will help in this case. If the attenuation performance of the cable is not smooth, then the ATM signal will probably not be interpreted correctly even though the cable installation passes Cat 5 requirements below 100 MHz!


STANDARDS BY DEFINITION ARE DERIVED BY CONSENSUS.

The ANSI/TIA/EIA-568-A Commercial Building Telecommunications Cabling Standard took years to ratify. Portions have become obsolete. Politics, Politics, Politics!

For example, "Delay Skew" is an addendum to the ANSI/TIA/EIA-568-A specification that requires another test be performed on the cable before it leaves the manufacturer. The TIA task group has rejected suggested names for the addendum (Category 5.1 or Cat 5-1997), and has elected not to have the cables that would comply with the new standard marked differently from the other seven billion feet of four-pair cable already manufactured and currently installed in North America.

The only way to know for sure if your cable meets this new requirement will be to get a copy of the actual product specification the manufacturer used to make the exact cable you purchased at that time. When was the last time you consulted the cable manufacturer's spec sheet? So, enhancements to cable can only be determined by looking at exactly what parameters the manufacturer has tested and guaranteed.

Performance is directly related to the chemical compounds used in the manufacture of cable. There are more than 105 different electrical designs of plenum cables, including 15 high-end Cat 5 plenum designs and 33 standard and high-end nonplenum designs - all with varying electrical performance characteristics, yet still Cat 5-compliant. F.E.P. (Fluorinated Ethylene Propylene) remains the dominant insulating material for high performance constructions.

A high-speed system must display Category 5 characteristics from input to output: across all connectors, cross-connects, patch panels and outlets. Assuming our Cat 5 cable tests out at 155 MHz, we still must contend with the variety of the components. Some of the plenum construction used different numbers of Polyolefin insulated pairs mixed with the FEP insulated pairs. This mixing of different materials can cause the propagation delay skew to exceed the 45 ns specified in the revised TIA-568 standard and has resulted in a recent addendum. (Mo' Politics!)

Immediately after the standard was issued, the committee came out with TSB-36 (Technical Systems Bulletin) for "Additional Cable Specifications for Twisted-Pair Cables", which defined the new Category 3, 4 and 5 electrical performance requirements (based on the Levels Program and the work done at NEMA [National Electrical Manufacturers Association] and ISO).

Frost & Sullivan, an information company specializing in high-technology market research, addresses the effect of standards on cable manufacturing in its 1997 report on the North American Premises Wiring Transmission Media Market, stating, "Standards have become so prevalent that brand awareness has become less of an issue. . . Because of this, many manufacturers tend to minimally meet specifications, which in turn fosters a market environment where the products become commodities. . . As a result, the advent of standards has impeded manufacturers from developing products that exceed the qualification of standards."


Five years ago, we were told that Cat 5 would be the ultimate cable design in the horizontal cable infrastructure. Now, it appears that "headroom" and "structural return" concerns will open the books again (with the help of the new Level '97 Program). The Anixter Levels '97 Program is based on a stringent purchasing specification that requires Anixter suppliers to qualify their high-performance unshielded twisted-pair products.

The Levels '97 Program aims to clear up the confusion in the industry, fill holes in existing standards, and provide its customers with the information they need to select the best, most cost-effective product for current and future applications. To accomplish these goals, Anixter has worked with 40 leading structured cabling and systems manufacturers to create an unbiased method of specifying cable. Levels '97 sets guidelines for electrical bandwidth in excess of 100 MHz by reaching for a performance mark that has more than twice the actual usable electrical bandwidth of the current Cat 5.

The New Levels:

  • Level 5 : Cable specified as Level 5 must meet the stricter requirements for Category 5 as spelled out in the international standard ISO 11801, which allows cables meeting its requirements to be used globally. Both Category 5 and Level 5 achieve 10 dB ACR at 100 MHz. However, Level 5 tests for delay skew-the difference in timing between pairs in a cable-while Cat 5 manufactured before December 1996 does not. In fact, the current standard says it is up to the user to determine if cable was tested to meet delay skew. Also, Level 5 cable must meet stringent four-pair NEXT requirements, referred to as powersum testing. This test measures the crosstalk influence from all pairs in the cable on each pair, providing a more accurate picture of the cable in operation. Level 5 requires a powersum measurement to 80 MHz, which assures that this cable can also be used for four-pair technologies-unlike Cat 5, which allows for only using two pairs at a time. Furthermore, splicing of the insulated conductor is not allowed in the Levels program. Manufacturers of category-type cables can splice together pairs that break, possibly decreasing performance. (Since 1989, random tests have been performed to weed out spliced cables.)

  • Level 6 : Increases UTP cable performance by requiring 10 dB of ACR at 155 MHz. In addition, Level 6 cable must meet more stringent four-pair NEXT (powersum) requirements than Level 5, ensuring a performance level suitable for the newest four-pair-based network protocols through 100 MHz.

  • Level 7 : A new generation of recently launched products that meet at least twice the Cat 5 bandwidth requirement constitute Level 7. Level 7 cable achieves 10 dB ACR at 200 MHz and must be powersum-tested to an even higher NEXT value than Level 6. Ideal for future bandwidth-hungry applications, Level 7 cable can support multiple applications at different frequencies under one jacket, and will support Gigabit Ethernet at 100 meters.

Levels '97 ensures the quality of UTP cable. High-performance unshielded twisted-pair products are tested for compliance with the specification through a lot sampling procedure at the Anixter Structured Cabling Lab.

ALL CABLING PRODUCTS CERTIFIED TO LEVELS '97 MUST:

  • Fully meet the electrical requirements for the level.

  • Be marked with a sticker indicating level of performance met.

  • Come from a manufacturer registered to ISO 9000.

  • Be manufactured with only virgin materials.

  • Not include factory splices in insulated conductors.

Furthermore, manufacturers of levels-rated cable must submit initial qualification test data and agree to annual follow-up retesting at the Anixter Structured Cabling Lab for three samples taken randomly from Anixter stock.

The ultimate benefit of the Levels '97 program is a more reliable network with less down time, which is especially important as more companies depend on their systems to handle mission-critical applications. As Gary Conrad, Anixter senior vice president-structured cabling systems, notes, "We're uniquely qualified to serve as customer advocates, which is what Levels '97 is all about. We understand the needs and wants of both the installer and the manufacturer, and we can help both sides deliver a reliable, efficient network today and in the future."

As for the future, Anixter will continue to take a proactive stance in the industry and continue to revise its cable-performance specifications program - Levels '97 is the ninth revision to date-as technology and the needs of customers dictate.

When announced in April, Levels '97 defined the performance characteristics of unshielded twisted-pair (UTP) cabling beyond 100 MHz, a parameter necessary for advanced applications such as intranet technology, three-dimensional imaging, multimedia programs, video to the desktop, computer-aided design and broadband video.

For more information, go to www.anixter.com

 

  Friday, July 18, 2003
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