Businesses today thrive and grow based on their ability to link employees, customers, suppliers, and distributors in local area networks (LANs). According to industry research by Cahners In-Stat Group's MarketAlert in 1999, about 60 percent of employees in the United States had access to an employer's internal network. By 2003, this figure is expected to grow to 80 percent. The demand for high-speed, high-performance, and high-bandwidth communications has never been greater, driven by the increasing role of computers and explosive growth of Internet-based communications.
At the heart of these LANs, and playing a key role in their performance, is the structured cabling system. Launched in the early '90s, the concept of a structured architecture for LAN and premise cabling was formalized as EIA/TIA 568-an interoperability standard for communications cabling developed by the industry to ensure cabling components and networking equipment would work together effectively to deliver the specified level of performance.
Futureproofing: hype or reality?
There has been much talk in recent years about futureproofing the network cabling system. But, lacking a crystal ball, is futureproofing really possible? If we examine the trends today and in the recent past, we can gain some idea of how networks can be structured with ample headroom for future developments.
For the most part, the installed base of cabling today will drive the electronics technologies of tomorrow, largely because businesses want to protect their existing technology and communications investments.
Next-generation cabling and electronics
LAN technology has experienced increasing capacity over at least five generations. These include Ethernet,10Mbps; fiber distributed data interface (FDDI), 100Mbps; Fast Ethernet,100Mbps; asynchronous transfer mode (ATM), 155 Mbps; and gigabit Ethernet (1,000 Mbps). Technical developments in unshielded twisted pair (UTP) premises cabling-Category 3, 4, 5, and 5e-and networking electronics have likewise advanced to keep up with increasing bandwidth requirements.
The next generation of high-performance cabling, intended for Category 6, has been available in the marketplace since 1997 and has been deployed in many installations. As a result, a study group has been formed to investigate the feasibility of creating a 10 gigabit Ethernet standard.
If we compare the electronics used for 10baseT with today's electronics (100baseT and 1000BaseT), today's not only run faster (more MHz) but also run smarter (more bits per MHz). We have gone from signals with two voltage levels (NRZI) to three levels (MLT3), and even as many as five voltage levels (PAM 5). Systems have moved from using one pair for sending and a second pair for receiving data to using each of the four pairs-for sending and receiving data simultaneously. This system complexity requires next-generation cabling performance.
These new faster, smarter encoding schemes do not just require higher pair-to-pair crosstalk performance or less attenuation, but also require more sophisticated cable specifications. One of the earliest examples of this is delay skew. In two-pair systems, delay skew is not a concern. With today's four-pair technology, however, timing of parallel signals is critical. More recent examples of today's critical parameters include return loss, powersum ACR, and powersum equal level far-end crosstalk (ELFEXT).
With the introduction of gigabit Ethernet, return loss became significant for cable manufacturers and specifiers. Critical to gigabit Ethernet, return loss measures impedance mismatches, which cause phantom signals that can lead to network re-transmission and overall degradation. Return loss of a cabling system is an excellent measure of the quality of the entire channel, because it qualifies individual components as well as how well they work together in a system.
Return loss in network cabling is covered by IEEE 802.3ab gigabit networking specifications. This requirement was further implemented into TIA/EIA's TSB95 and now the ANSI/TIA/EIA 568-A-5 enhanced Category 5e cabling standard.
Powersum ACR measures the speed potential of an interconnect solution, with greater Powersum ACR delivering higher bandwidth and increased network throughput capabilities. Powersum ELFEXT indicates the degree to which transmissions are affected by other data traffic and assures that the signal gets to where it is going.
These new parameters are critical to ensuring interconnectivity performance, Structured cabling system designers, integrators and installers should be familiar with these specifications when selecting and specifying cable system components.
Careful installation is critical
Proper installation techniques are a key factor in achieving maximum network performance of the structured UTP cabling system. Installation damage is one of the most common causes of degraded performance in Category 5, 5e, or 6 cabling. Even when following recommended methods of installation, channel failure due to return loss can occur as a result of the rigors of installation or commonly performed installation practices designed to facilitate moves, adds, and changes.
As an example, many installers routinely install cabling with excess material coiled up into what is known as a service loop. The intent is for this loop to be uncoiled at a future date if changes are required. Unfortunately, with many cables, this service loop can cause severe degradation of channel return loss and near-end crosstalk (NEXT). Another cause of reduced return loss from installation is cabling being bunched up into the outlet box behind the wall outlet. This bunching causes the pairs to open up and can reduce return loss. These two installation practices combined can be responsible for up to 3 to 5 dB degradation of return loss in a "correctly" installed channel. These perils can be avoided by selecting advanced bonded-pair cables that are not susceptible to this kind of installation damage.
The way of the future: a total systems approach
What do today's businesses expect of their high-speed data communications networks? For their mission-critical and business-critical LANs, they require virtually flawless transmission, integrity and security, as well as 24x7 uptime. In short, they demand solutions that work and last.
Therefore, many leading industry suppliers are forming alliances to provide well-designed, end-to-end structured cabling systems that meet the needs of virtually every networked application. The advantages of this total systems approach go far beyond the products alone-the cables, connectors, hardware and electronics. In addition to offering the convenience of a single source of supply from a vendor you trust, the longer-lasting benefits include product selection expertise, assured performance and connectivity, and extended performance warranties that protect your investment and ensure it can be upgraded far into the future.
ROTH is a technology development specialist for Belden Electronics Division, Richmond, Ind. He can be reached at firstname.lastname@example.org.