Passage of Category 7 hinges on stp connector interfaces

There are many end-users and installers out there who will be the first to say that shielded twisted-pair (stp) cable is bulky, difficult to install, and expensive. And many will go so far as to say that is all anyone really needs to know about it. After all, unshielded twisted-pair (utp) and fiber-optic cable have produced extremely successful results for the North American premises-cabling market. And the triumphs of utp and fiber will continue, but that does not mean stp and the proposed stan

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iso, iec eye RJ-45-compatible proposals but consider a non-RJ-45 design as "plan B."

Mark A. DeSorbo

There are many end-users and installers out there who will be the first to say that shielded twisted-pair (stp) cable is bulky, difficult to install, and expensive. And many will go so far as to say that is all anyone really needs to know about it. After all, unshielded twisted-pair (utp) and fiber-optic cable have produced extremely successful results for the North American premises-cabling market. And the triumphs of utp and fiber will continue, but that does not mean stp and the proposed standards to regulate its implementation will go away.

Europe is making sure of that as its strives to see through the next generation of stp, for it is the preferred medium there, especially in Austria and Germany. "In North America, a contractor would say, `I don`t want to mess with that stuff,` " says Tony Beam, director of global systems marketing for amp Inc. (Harrisburg, PA). "However, Europe, especially central Europe, is very comfortable with stp cabling systems."

For almost two years, committees and subcommittees of the International Organization for Standardization and the International Electrotechnical Commission (iso/iec--Geneva) have collaborated to hammer out a Class F/Category 7 standard. The proposed standard will optimize bandwidth, versatility, and ease of use for stp installations. Although the proposed Category 7/Class F standard is limited to a bandwidth of 600 megahertz, several proposed connector interfaces aim at boosting bandwidth over twisted-pair cabling that is needed for applications like broadband video. The bandwidth-hungry video application has a frequency requirement of more than 860 MHz. A single Category 7/Class F channel can also support connections of other diverse applications such as analog voice and high-speed local area networks (lans).

"The most critical issue to resolve is the connector interface to finalize the standard and provide 600-MHz transmission," Beam says. "The cable is already capable of meeting the standard. The connector interface is at the heart of finalizing it."

At a meeting in Cancun, Mexico, last January, the iso/iec`s joint technical committee, Working Group 3, which deals with cabling specifications, and the iec`s Subcommittee 48, which reviews connector specifications, agreed to select one rj-45-compatible interface out of two and one non-rj-45 stp connector interface from a field of six proposals.

During that meeting, the committees reviewed presentations from Alcatel (Malvern, PA), amp, The Siemon Co. (Watertown, CT), and Thomas & Betts Corp. (Memphis, TN). The Siemon Co. and Thomas & Betts submitted non-rj-45 proposals, while amp and Alcatel submitted designs that incorporated the rj-45 compatible design. Telesafe (Norway), Sofim (France), btr (Germany), and bks (Switzerland) also submitted non-rj-45 proposals. In the end, the committee agreed that interfaces should have direct backward-compatibility, which stipulated the rj-45 design. That meant proposals from amp and Alcatel were subject for further review, and both will be the subjects of another meeting of the iso/iec in Berlin later this month. An assessment panel of the iso/iec`s Subcommittee 25 will be conducting a survey of the non-rj-45 proposals, narrowing the field to one as plan B.

"We decided to take a neutral approach," says Dunn Harvey, senior manager of standards at nordx/cdt Inc. (Pointe- Claire, QC, Canada) and Canada`s only delegate of the iso/iec`s joint technical committee. nordx/cdt is not involved in the stp market, but other cdt companies like montrose/cdt (Auburn, MA) are. The ad-hoc assessment panel will look at the interfaces with rj-45 jack designs as well as the six other proposals with non-rj-45 designs. "This ad-hoc committee is supposed to report back to us at the end of June with a fallback connector," he says. "We will vote on the number one rj-45 connector interface, and we will also vote on the fallback interface connector."

As for amp and Alcatel rj-45-design proposals, Harvey says the iso/iec has asked them to combine their efforts to develop one connector. amp`s Beam and David Hess, Alcatel`s vice president of product marketing, declined to comment on whether the two companies are working together. "We`ve been asked to work together, but we do not have any official statement on that. As far as I know, neither of us does," adds Hess, who is also the secretary and vice chairman of the U.S. technical advisory group to iso/iec Subcommittee 25. "Obviously, we are going to be talking to amp about something. It would not be prudent to show up in Berlin without investigating the possibilities," he says.

Comparing interfaces

There are a number of similarities between amp`s and Alcatel`s proposals. The two interfaces aim to offer performance beyond Category 7`s 600 MHz. They are also mechanically compatible with the rj-45 design and aim to be backward-compatible with Category 5 and should be with proposed Category 6 connectors. The connector interfaces will also be available in stackable, multiport, and side-entry versions with 1- and 2-pair modularity provided by an adapter. Possible combinations of pairs are pins 1, 2, 7, and 8 for Asynchronous Transfer Mode; 1, 2, 3, and 6 for Ethernet, and 3, 6, 4, and 5 for Integrated Services Digital Network and Token Ring. Pins 0 and 9 are grounds.

But there is one major difference: amp`s and Alcatel`s stp conceptual connector interfaces may aim to be backward-compatible, but they are not attuned with each other, says Marcus Rademacher, product marketing manager for amp in Langen, Germany. "Both proposals are rj-45-compatible, but they are not compatible with each other," he adds. "This is something that needs to be sorted out."

Hess agrees: "It`s not clear how they can be made compatible, and that is being explored."

According to Alcatel`s proposal, its GigaGate connector interface jack will have the normal eight contacts of an rj-45 design and will have four additional pins at the bottom of the jack, two in each corner. The plug will also incorporate a switch that shifts between high or low transmission speeds. "For high-speed, Category 7/Class F performance, the extra four contacts are used instead of the upper four," Hess says. "That allows the use of four separately shielded transmission paths through the connector. The isolation gives us the crosstalk level--at least 30 decibels across the board--that we were looking for."

The protruding part in the front of the GigaGate plug, he adds, closes the contacts of the switch. The result is no signal transmissions occur on the middle, upper two pairs of the jack. Only pins 1, 2, 7, and 8 transport signals, "enabling a very good crosstalk performance." A normal rj-45 configuration is achieved with pair one running over pins 4 and 5, while pair three runs over pins 3 and 6, the presentation indicates.

amp`s Category 7 modular plug and connector system will use flexible, multisurfaced, printed circuit boards instead of banded wire pins. "The whole idea is to have eight totally shielded wires, and it works like on the coaxial principle," Rademacher says. "When the jack and plug meet each other, everything around the contact zone is shielded."

While the rj-45 design seems to be the format of choice, Alcatel`s Hess says the non-rj-45 design will not fade away. "There is a lot of nice work there, and there`s a lot of commercial interest there as well," he adds.

One non-rj-45 stp connector interface design proposal comes from Thomas & Betts, a company with deep roots in the stp market that has signed an agreement with ibm to develop structured-cabling products for the PC giant`s Advanced Connectivity System. Several telephone calls to officials at Thomas & Betts to learn the details on the company`s connector interface proposal were not returned.

Another non-rj-45 connector interface proposal comes from The Siemon Co.`s tera system. "We sat down and we asked ourselves, `What are the key characteristics that would give us Category 7 transmission performance?`, and we concluded that complete isolation of the pairs from each other is the key for Category 7," says Denny Lo, engineering group leader at The Siemon Co.

With Category 5 and the enhanced versions that have made their way into the market, Lo says the key to good transmission performance is to design in precise amounts of capacitive and inductive compensation between contact pairs to offset inherent crosstalk in an rj-45 interface. "That rj-45 interface is a liability when you are trying to achieve Category 7 performance," he adds. "In our case, as with some of our competitors`, we ditched the rj-45 design and we got rid of the liability."

The tera outlets, Lo says, have features and benefits similar to those of Siemon`s Category 5 and 6 connectors. A slim, compact design allows outlets to be stacked side-by-side or inserted from the front or rear of the faceplate. Outlets also feature a hinged door to prevent exposure to dust and other contaminants.

"The plugs and outlets take up very little space, and they can be terminated quickly. We developed a special tool as well as some innovative techniques that allow for fast termination," Lo adds. "I can terminate in about two-and-a-half minutes."

In addition, the tera system, according to Lo, allows a cable to support up to four applications at performance levels beyond 600 MHz. "A non-rj-45 design gives you the ability to be completely modular. In addition to using a 4-pair plug in an outlet, you can also have combinations of 2- and 1-pair plugs all sharing the same outlet," Lo says. "The pairs are so isolated from each other that we have been able to successfully demonstrate acceptable crosstalk performance up to 1 gigahertz." We had to stop at 1 GHz because the test equipment couldn`t handle it."

STP and North America?

One question remains: Will stp make its way into the North American premises-wiring market if and when the Class F/Category 7 standard is finalized? Beam and Lo say it is highly unlikely it will become a commodity here, while Hess believes once the standard is finalized, a medium that provides extremely high bandwidth will be available.

According to Beam, amp expects very little penetration of Category 7/Class F systems into the North American marketplace. "The industry here has a preference for unshielded systems, and fiber presents a more viable option," he says, adding that if an stp system were installed in North America, it would probably be driven by a European influence. "We expect North America to shift from utp to fiber, and what little knowledge North American consultants, contractors, and designers have of stp is often referred to in a negative light."

Lo says if stp makes its way into the market, it would most likely be for "applications like broadband video or for information-intensive applications that are used on financial trading floors, for example.

stp proponents, namely the Germans, Hess explains, initiated the movement. stp provides more bandwidth than utp. "What`s holding its popularity up here is the presence of very successful results using utp, which used to be known as telephone wire," he says. "Up till now, it has been assumed that some type of connector was needed to extract the bandwidth from stp. Alcatel and amp have shown that getting that bandwidth can be done with rj-45-compatible connector interfaces. We`ve both demonstrated with models that stp is feasible."

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amp`s conceptual stp plug and jack connector system for the proposed Category 7 standard would use printed circuit boards instead of pins that are normally found in the rj-45 design.

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Alcatel`s concept for an stp plug and jack to meet proposed Cate-gory 7 performance is modeled after the rj-45. Although both amp and Alcatel hope to offer backward-compatibility with Category 5 and 6 connectors, their concepts are not compatible because of a difference in design.

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The Siemon Co. has already brought an stp connector interface to the market that meets proposed Category 7 performance requirements. The tera system is one of six non-rj-45 designs that committees and subcommittees of the iso/iec are reviewing.

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