Several cabling options are available to support this latest technology. Which one makes the most sense? I could tell you what you've always heard - install fiber and it will be the last cabling infrastructure you will ever need. That's the simple answer, but unfortunately it does have limitations especially with respect to affordability. Fiber may surely be the best choice in that it has the most bandwidth and is easily upgradeable to future applications that are yet to be developed.

If fiber is your preference, there are several options on the market providing different bandwidth capabilities based primarily on the distance the signal needs to travel and how much you want to spend. Singlemode fibers are essentially the same so there are no secrets there. Selecting a multimode fiber, however, is not as easy. Various multimode fiber types are available today based on how much you have to spend and how far your 10 Gigabit signal needs to travel. Keep in mind that the more bandwidth and distance required increases the cost and the performance. Installing a multimode fiber that is not standards based just because it is less expensive even though it will meet your distance requirements today may not make the most sense.

Twisted Pair Copper Options

Here's where things get more complicated because there are so many choices to make. What are the options? How can you be assured that you are installing a cabling infrastructure that will confidently support 10 Gigabit Ethernet?

Let's begin by reviewing what we know to be fact. I already mentioned that IEEE has released a standard stating that 10GBASE-T can be deployed over twisted pair cabling. The IEEE 802.3an standard does state what cabling requirements are needed for this new technology. One thing that's important to note is that the bandwidth required for 10GBASE-T is 500 MHz. The chart on page 3 reflects the IEEE 802.3an standard.

Look at all the cabling options for 10GBASE-T! Hold on a minute. There are some exceptions that need to be explained before you get too excited.

The chart indicates that Cat 6 will support 10GBASE-T but only to a limited distance. 55 to 100 meters is the supported distance but that is achieved only if cable runs comply with TSB-155. TSB-155 is a TIA standard entitled, "Additional Guidelines for 4-Pair 100W Category 6 Cabling for 10GBASE-T Applications." This standard describes additional guidelines for Category 6 cabling that has been installed in accordance with TIA-EIA-568B.1 to support the IEEE 802.3an 10GBASE-T application standard. This standard has raised the bar to the 500 MHz bandwidth requirements for the traditional performance parameters such as Insertion Loss, Pair-to-Pair NEXT, PSNEXT, Pair-to-Pair ELFEXT, PSELFEXT, etc.

The TIA standard also describes another parameter, Power Sum Alien NEXT loss - the most crucial parameter for successful deployment of 10GBASE-T. Alien NEXT is the coupling of a signal from one cable to an adjacent cable. All cables in a bundle will produce some degree of ANEXT which must be mitigated by some means in order to support 10GBASE-T. Standard compliant UTP Cat 6 by design is not capable of controlling ANEXT to any degree especially for adjacent cables. Separating UTP cables or connectors slightly would solve the problem but that obviously creates other problems with real estate.

Can a Cat 6 cable run be tested for PSANEXT? Yes according to TSB-155. However, only two adjacent cables can be tested at one time. All of the other combinations that contribute to the degradation the 10G signal cannot be measured with existing field test instruments. Two PSANEXT loss tables are referenced in the TSB; one for 100 meters and one for 55 meters. If the numbers referenced in the 100 meter table are met then the cable run will supposedly support 10GBASE-T to that distance. If the 55 meter table numbers are met, then the cable run will support 10GBASE-T to that distance only. There are also tables for 100 and 55 meters for PSAELFEXT.

Now let's go back to the IEEE chart. IEEE does feel that 10GBASE-T will be supported in an existing installation up to 55 meters with a standard compliant Cat 6 cable. It's that 55 - 100 meter distance that they are unsure of. They are also indicating that confirmation of the cable per TSB-155 will ensure support to the applicable distance. The important thing to note is that there are no assurances that an existing Cat 6 cable run will support 10GBASE-T.

Are there any copper cabling systems that IEEE says will support 10GBASE-T without any conditional issues? Yes there are. The next one down on the list is the Cat 6 screened (shielded) twisted pair cabling. IEEE says this cabling will support 10GBASE-T to the full 100 meter distance; however it also references TSB-155. What do we know about shielded Cat 6 cabling? One thing's for certain, there are no ANEXT issues as the shield has automatically taken care of that for us. Most of the other parameters defined in TSB-155 extended out to 500 MHz are also easily met assuring full 100 meter support of 10GBASE-T.

The chart also refers to Class F as being capable of supporting 10GBASE-T to 100 meters. For those who are not familiar with this cabling, consider it a Cat 7 cable. It is also a shielded cable but considerably more robust; it has a higher bandwidth, it's more expensive, and is much stiffer than a Cat 6 shielded cable. It is predominantly used in the European community and is not readily available here.

One cable listed is a new Augmented Cat 6 cabling that is capable of supporting 10GBASE-T to 100 meters as well. The Augmented Category 6 cabling requirements are presently being defined by TIA and a standard should be released by the end of 2006 or sometime in the first quarter of 2007. This standard has raised the limits across all existing parameters, including the new parameters ANEXT, PSANEXT, and PSAELFEXT to 500 MHz. This standard will apply to both UTP and shielded cabling components.

An Augmented UTP installed solution can only be tested by sampling two adjacent cables in a bundle. Once again, this does not provide assurance that all combinations of ANEXT are not contributing to performance degradation in any way. One other thing that is significant is that the diameter of the UTP version is larger than the shielded version. In order to mitigate ANEXT issues from cable to cable, space is added which results in a larger cable. This is not necessary when there is a shield surrounding the pairs.

In conclusion, the best option in terms of performance is fiber. Copper cabling systems are still prevalent and may be the desired choice due to costs primarily associated with the equipment. A shielded cabling infrastructure positively ensures full 100 meter support especially since field testing of PSANEXT cannot be performed with the test equipment that exists and may never be capable of performing tests of all combinations. It is also smaller in diameter than the UTP Augmented Cat 6 cable while also being less expensive. Also, it is based on an existing standard.

Special thanks to Bob Zahr RCDD/NTS, for writing this article. Bob is Systems Engineering Manager at Tyco Electronics.