From the July, 2014 Issue of Cabling Installation & Maintenance Magazine
Copper-based 40GBase-T continues to make strides toward standard and market reality, while multimode-fiber-based systems get put to use.
For the 40GBase-T copper-based transmission technology, as well as the Category 8 cabling systems built to support it, the famous saying from Chinese philosopher Lao-tzu rings very true: A journey of a thousand miles begins with a single step. Every step along the way to these technological developments marks a milestone of sorts, and ultimately the finished products-standards, products, systems-will be an accomplishment akin to a thousand-mile walk. Progress is being made on each front; this article will focus primarily on the efforts of the Telecommunications Industry Association (TIA; www.tiaonline) to specify Category 8 cabling systems for deployment.
The TIA standard-development subcommittee that is working on Category 8-TR-42.7-met most recently in early June along with the overall TR-42 Telecommunications Cabling Systems Engineering Committee. During those June meetings the overall TR-42 committee approved a project authorization for High Performance Structured Cabling (HPSC) Applications. Though that official approval took place in June, the TIA had publicized the effort a month earlier. On May 6 2014, we reported that the TIA had issued a call for interest on behalf of TR-42.7 to develop a telecommunications systems bulletin (TSB) addressing HPSC applications.
Set to spec
When announcing the call for interest, the TIA explained, "The TSB document, initially titled 'High Performance Structured Cabling (HPSC) Applications,' will provide usage details for deploying Category 8 structured cabling in data centers and other premises environments that will have a need for data rates greater than 10 Gbits/sec. The information in this TSB document can then be used when designing networks and facilities for high-speed applications, including 40GBase-T, which is currently under development as IEEE 802.3bq."
According to the TIA, the task group's scope "is to identify, analyze and recommend use cases-e.g. switch fabric architectures, end-of-row, and top-of-rack-for high-performance structured cabling application environments utilizing technologies such as 40GBase-T … These use cases can be incorporated in data center or premise designs including equipment rooms, server rooms, laboratories, and high-bandwidth technology spaces." The TIA said stakeholders include cabling system designers and installers, IT professionals, cable manufacturers, datacom-equipment designers, datacom-equipment manufacturers, and PHY (silicon) suppliers, among others.
"Since its inception in the early 1990s, twisted-pair Ethernet, or Base-T, has provided end users and designers of high-speed computing networks with the most widely adopted physical interconnect technology ever developed," the TIA further explained when announcing the task-group call-for-interest. "The combination of twisted-pair Ethernet's low cost, high availability, structured topology, common physical interface and autonegotiation capabilities makes it an attractive option for the transmission of data and low-voltage power in office and data center application environments when compared to other available interconnect technologies. As twisted-pair Ethernet continues to evolve with increased data rates and improved performance, users of this technology will have a migration strategy for their computing networks that provides a high degree of flexibility and longevity."
The use cases and value propositions for 40GBase-T and Category 8 are highlighted by short-reach data center connections. Per the IEEE 802.3bq's specification, the TIA's TR-42.7 is working to establish a 30-meter channel specification for Category 8.
A far reach?
In a recent post to Panduit's Data Center Blog (www.panduitblog.com), the company's solutions marketing manager for application solutions, Tom Kovanic, discussed the appropriateness of this 30-meter reach specification. In the cleverly titled post "Reach for 40GBase-T," Kovanic noted that the length limit "is a tradeoff between power dissipation of the silicon physical layer (PHY) IC [integrated circuit] driving the cable, the complexity of the PHY which would impact cost, the implementation of the channel, and the reach of the link. The question is: Is 30 meters long enough?"
Devoting the rest of his post to answering that question, Kovanic continued, "Copper cabling, of one type or another, is the preferred media type for connecting servers to the first layer of switches. Deploying a 10G Ethernet copper link with Category 6A cable and RJ45 connectivity, or using SFP+ direct attach copper (DAC) cable assemblies, is less expensive than deploying those links with fiber optics. One other problem with DAC cables is compatibility issues. DAC cables have a memory chip on them that provides information such as the vendor, and this information is then sometimes used to shut down the port. Structured cabling does not have this problem.
"Putting aside 40G breakout cables," Kovanic continued-promising to cover these breakout cables in a future blog post-"the current copper solution for 40G Ethernet limits the architectures one can deploy. 40G Ethernet QSFP+ DAC cable assemblies have a reach of 5 to 7 meters. This means that one could use them to deploy a top-of-rack (ToR) architecture or where one uses a ToR switch to service two racks of servers, but that is about it. QSFP+ DAC cable assemblies cannot be used for most end-of-row (EoR) implementations or other architectures. Additionally, DAC cable assemblies are a point-to-point solution and therefore cannot support a structured cabling design. A structured cabling architecture uses a permanent link, or backbone, and patch panels and patch cords that connect the permanent link to equipment. This provides the maximum flexibility when it comes to deploying equipment and allowing changes in the future. 40GBase-T provides a flexible, structured cabling solution for 40G Ethernet."
Kovanic described 40GBase-T, with its 30-meter reach, as "a perfect solution for deploying 40G in an EoR architecture, not to mention a ToR architecture. Thirty meters is certainly long enough to implement virtually all implementations of an EoR."
While 40GBase-T may be a bit of perfection when it comes to end-of-row network schematics, the marketplace's understanding of the still-under-development Category 8 cabling technology that will support 40GBase-T can be less than perfect. As is often the case when products and systems exist primarily (or exclusively) in the hypothetical or research-and-development realm, the systems are not yet concrete for professionals who will be the ultimate users of them. That is true today for Category 8. Recently market researcher Sarah McElroy published a "fact and fiction" document on Category 8 cable (see sidebar).
Fiber options
Meanwhile, as Category 8 and 40GBase-T take the steps along their thousand-mile journey, the ability to transmit information in a local area network at 40 Gbits/sec has been well within reach for years for users opting for fiber-optic transmission systems. In 2010 the IEEE ratified the 802.3ba standard for 40- and 100-Gbit/sec Ethernet transmission over optical fiber.
In October 2011 we published an article by Leviton Network Solutions' (www.leviton.com) senior director of product management Gary Bernstein, titled "Are you ready for 40 and 100G?" Based on a white paper also authored by the company, Bernstein's article might be looked at as years ahead of its time because it foresaw the migration users would make from fiber-based 10- to 40- (or 100-)Gbit/sec Ethernet networks and in particular the connectivity options associated with such a migration.
Advocating for the use of 24-fiber MPO-style connectors as opposed to 12-fiber MPOs in a 40G-ready system, the article posed this question: "Is your network cabling optimized for inevitable growth? Create a simple, cost-effective migration path by installing a structured cabling system that can support your future 40/100G networking needs. An ideal system will include the following. A) One simple, modular connectivity solution for legacy 1G and 10G applications that is also compliant to 40G and 100G. B) One standardized connector theme able to support future high-bandwidth applications. C) Preconnectorized components compliant to all current and anticipated industry standards."
As we have covered more recently, the parallel-optics technology used for 40G requires 8 fibers per link (10 Gbits/sec/fiber x 4 fibers x 2 directions). Likewise, the soon-to-be-completed 100GBase-SR4 will specify 25 Gbits/sec/fiber x 4 fibers x 2 directions. So just as 8 is a "magic number" in copper cabling (i.e. Category 8), it has emerged as a number of importance in multimode-fiber-based transmission systems as well. Leviton and some other solution providers emphasize that a 24-fiber connector is a clean multiple of 8, thereby enabling 3, 8-fiber circuits to be connected. Back in 2011, Bernstein advised, "For 40G networks, choose a 24-fiber MTP wiring scheme that delivers true 100-percent fiber utilization-no dark fibers or empty pins." The idea soon will apply to 100G as well.
If 40G networking is in your future, the steps you take today can significantly influence the path to that destination, which may be far closer than the thousand miles of Lao-tzu's wisdom.
Patrick McLaughlin is our chief editor.
Separating Category 8 fact from fiction
Sarah McElroy, a research analyst with IHS, recently published a document titled "Category 8: Unraveling Fact from Fiction." With IHS's permission, we are reproducing that document here.
In the few months that I have been researching the network cabling market, I have heard a wide variety of perspectives and opinions about the pending introduction of the Category 8 copper cable, which will support 40-Gbit/sec Ethernet. Never have I encountered a topic where I have heard such opposite viewpoints expressed. In the case of Cat 8, the "facts" I hear from one supplier have completely contradicted the "facts" I hear from another, especially when relating it to a comparable fiber offering. For this reason, I have set out to clear up some misperceptions associated with Cat 8 copper cable.
Cat 8 is even larger in diameter than Cat 6A: TRUE
While it is true that Cat 8 is slightly bigger than Cat 6A cables, the difference in size is far less than what is often claimed. A source close to the standards creation has stated that Cat 8 cables will only be a few hundredths of a millimeter larger in diameter. When looking at the two cables side-by-side, the naked eye would not recognize the difference in size.
Compared to fiber, however, there is certainly no contest with regard to size. Fiber-optic cables are often anywhere between one-fourth to one-half the size of a copper cable. One fiber is about the same size as a human hair, so these cables will inevitably be only a fraction of the size of copper cables, especially since they do not require shielding.
Size is a concern due to the limited space available in a patch panel or switch, especially as densities increase. For example, there are now 48-port patch panels, and with the current size of copper cables and connectors, there is barely room to fit all those cables. There is really no room for cable or connector size to expand if high densities are to be achieved. Airflow is also a concern because it becomes increasingly difficult to get adequate airflow to switches with higher densities of cords attached to them.
The increased weight of Cat 8 cable will cause problems for cable management and switches: FALSE
Cat 8 cable will indeed be slightly heavier than Cat 6A cable. However, a source involved with standards creation claims that the increased weight amounts only to a couple more pounds per reel of cable. This small amount of extra weight is not anticipated to cause problems for cable management or to create a dangerous amount of weight pulling on switches. Fiber-optic cable, by comparison, is much lighter than copper and, additionally, will never suffer from the added weight of shielded layers.
Cat 8 requires more power than fiber-optic cable to run at 40-Gbit/sec speeds: TRUE
It is true that copper-based systems require more power to run at high speeds than fiber-optic-based systems do. The power that will be required to run a 40GBase-T system can be depicted as a U-shaped graph, with power on the vertical axis and frequency on the horizontal axis. Thus, there is a certain range of ideal frequencies-at the bottom of the "U"-at which the power needed is lowest. While it is possible to optimize the power used by the Cat 8-supported 40GBase-T system, it will still always exceed that required by a fiber-based 40G system.
When thinking about power usage, heat becomes an additional consideration. Because copper-based systems require more power, they also generate more heat than fiber-based systems, and contribute to the need for increased data center cooling efforts.
Cat 8 cables will be standardized for a shorter length: TRUE
The Telecommunications Industry Association (TIA) did a survey that showed cable lengths of 50 meters or less will cover 90 percent of the cabling needs in a data center. However, to make absolutely sure that they did not run into the same problems that prolonged the application of Category 6A-supported 10GBase-T, the Institute of Electrical and Electronics Engineers (IEEE) decided that the standard for 40GBase-T be created for 30 meters. This may be completely adequate for some data centers; however, those needing cables longer than 30 meters will be limited by this length, and may find fiber-optic cabling to be the most viable option.
Cat 8 does not have as much longevity as fiber-optic cabling: TRUE AND FALSE
It is true that fiber-optic cabling lasts more than one cycle of install, and because of this, it usually lasts much longer than the typical copper installment. Therefore, when looking purely at the length of time a deployment will last, fiber usually wins. However, Cat 8 copper (along with all other category cables) provides another type of longevity in that it supports Base-T applications that autonegotiate. Therefore, it has the ability to endure a multistage deployment. Because of Base-T's autonegotiation capabilities, customers are able to upgrade electronics gradually instead of installing an entire new deployment all at once in order to implement a 40-Gbit/sec system.
Copper is easier and better understood than fiber: HONESTLY, THIS IS SUBJECTIVE
People don't like change, and that is just a fact. It is frequently claimed that copper is easier to install and all installers can do it. You do not need any extra training or certification to install or maintain a copper infrastructure. Proponents of Cat 8 will continue to cite this as a compelling reason to stick with a copper infrastructure to satisfy 40-Gbit/sec needs as opposed to switching to fiber optics. To be fair, there are many differences, and terminating fiber cables is definitely a bit trickier. However, fiber has been around long enough by this point that there are many skilled installers, the fiber isn't as fragile as it used to be, and many of the concerns surrounding installation difficulties no longer apply.
While fiber continues to be more competitive, copper continues to strive to achieve the quality and speeds that fiber handily provides. Will contractors and customers stick with what they know, or try something new? We will have to wait and see. Hopefully we won't have to wait too long. The TIA will likely have standards completed by the end of 2015, while the IEEE standards are predicted to be completely shortly after, perhaps by the beginning of 2016.
