Key Steps in Designing and Installing a Structured Cabling System - Page 2

Just as Fast Ethernet was initially used in the Ethernet architectural hierarchy as a backbone technology to support Ethernet to the desktop, now Gigabit is going to be used primarily as the backbone technology to support Fast Ethernet to the desktop. The reason that Gigabit will be primarily utilized as a backbone technology initially is because although some servers and other high bandwidth users may necessitate Gigabit to the desktop, the cost of employing Gigabit to all but the most demanding bandwidth users is still relatively cost prohibitive.

In addition, network design issues are at play here. Any network design that has a backbone as part of the Ethernet Architecture will usually require that the bandwidth for the backbone should be exponentially higher than the desktop bandwidth, in order to support a large number of desktop users with any effectiveness. In other words, in order to support a large number of Gigabit-to-the-desktop users effectively, some other higher bandwidth application needs to be deployed as a backbone technology.

As of this writing, no higher bandwidth application yet exists in the Ethernet Architecture. But as we speak, the electrical components (hubs, switches and network cards) for 10Gigabit applications are currently being developed. Coupled with the eventual and inevitable drop in price of Gigabit networking, it won't be long before Gigabit will be randomly deployed as a desktop technology. In order to make sure that your network cabling system can properly support Gigabit, make sure that it is certified to minimum CAT 5E standards. In the computing world, Moore's Law states that computer processing speeds double every 18 months. Make sure that your cabling system is up to date so that you don't get left behind. And by the way, if your office is small enough that it only has one Telecommunications Closet, then Gigabit to the desktop would certainly work well in that environment.

CAT 5E
As stated previously in this document, CAT 5E was designed to support Gigabit Ethernet. The standards for CAT 5E were in the proposed stages before the EIA/TIA standards committee for well over a year before they were finally passed in late 1999. The reason that the old CAT 5 standards needed upgrading was because of some unforeseen problems with the way that the testing requirements were written for CAT 5 and the difference in the way that Fast Ethernet works compared to the way that Gigabit Ethernet works.

Basically, Ethernet and Fast Ethernet required just two pairs for signal propagation. One pair was used to transmit and one pair was used to receive. Although the CAT 5 standards required that all 4-pairs of the UTP cable be terminated and tested, each pair was tested separately and individually from the other three pairs.

With Gigabit, all 4-pairs operate simultaneously, transmitting and receiving, which creates more cross-talk issues. New "Power Sum" testing requirements needed to be addressed in order to ensure proper Gigabit functionality. Thus, the new CAT 5E testing standards were born. In a nutshell, Power Sum testing is a way of testing one pair while measuring the cross talk in the other three pairs. The added testing requirements for CAT 5E above and beyond CAT 5 are as follows: Delay Skew, Propagation Delay, Power Sum Near End Cross-Talk (PSNXT), Equal Level Far End Cross-Talk (ELFEXT) and Power Sum Equal Level Far End Cross-Talk (PSELFEXT).

And here's one more thing to keep in mind. Not all CAT 5E cabling is equal. The minimum Mhz rating for CAT 5E compliant cabling is 100 Mhz. There are various cables that exceed the minimum requirements. The extra bandwidth might come in handy. Although the minimum requirements for CAT 5E will support Gigabit applications, the lower the Mhz rating on your cabling, the lower your margin for error becomes. Therefore, the lower the Mhz rating of the cabling, the less room you have for installation errors. This will especially be of some consequence when the patch cords are installed (see Channel Link section below).

CAT 6
As of this writing, the standards for CAT 6 specifications are only in the proposed stages before the EIA/TIA committee. Therefore, there are no industry-wide accepted standards that everyone is agreeing on yet. But in this competitive business climate that we live in, manufacturers are always trying to get the edge on each other. They are all trying to beat each other to the punch, by being the first to release "CAT 6" compliant products. But since the standards have not been passed yet, these products can only rightfully claim that they meet the minimum specifications for CAT 6 standards as they now stand proposed.

If history is any indication, the standards will change a few times before they are passed and accepted in their final format. Most manufacturers have tried to build enough extra bandwidth into their products that no matter what specifications the EIA/TIA committee finally passes, most of their products now on the market should meet or exceed those product specifications. But it is important to note that no one can certify your present system to "CAT 6" specifications, since there are no final draft specifications. Testers can be set to test for the latest proposed specifications, and if your system passes this test, you now have a system that meets the "proposed" CAT 6 specifications in their latest incarnation. Keep in mind, that when the final revised standards are ultimately approved, it may be required that your system be tested again. Ask your contractor, who is responsible for the cost of re-testing.