Almost every data center manager has seen firsthand examples of data center cabling gone wrong, which is why a great deal of time and energy is spent on cabling planning and management best practices
This article will provide data center managers with an overview of current data center cabling offerings and the key differences among the cabling specifications. It will also address how to effectively select proper data center cabling and factors for data center managers to consider when matching cabling to the right application.
Primary considerations for data center cabling
Before deciding on which type of cabling to use, a data center manager should consider the following factors.
Applications and switching infrastructure. In addition to carrying traditional voice and data, the network is also transmitting video applications. This has created the need for a cabling system that is capable of transmitting simultaneous multimedia signals.
Switching infrastructure also drives cabling requirements. For example, data center managers increasingly require switching infrastructure capable of handling 10 Gigabit Ethernet (GbE). In order to take advantage of that potential bandwidth, the cabling infrastructure must be rated to that speed. Most frequently the switching infrastructure is designed to handle application requirements, and the cabling selection can be determined by the specified network infrastructure.
Bandwidth requirements. Category 5 is no longer supported and has been replaced by Category 5e, which is made to support 10Base-T, 100Base-T and 1000Base-T (GbE) applications. Category 5e systems are often sufficient, but data center managers running 1000Base-TX applications need to be sure to use Category 6 equipment; and those running 10GBase-T (10 GbE) will need to utilize Category 6a cabling (Category 6a is a minimum requirement for data centers to be ISO certified).
Port density and space constraints. Data center managers reviewing the aforementioned considerations might conclude that 6A is always the way to go. However, port density needs to be taken into account. It has become increasingly affordable to configure servers with at least four network connections (primary, secondary, backup and management), which has at least doubled the port density in a single cabinet. Therefore, data center managers need to evaluate cabinet selection and cable management in order to determine if there is enough space to use Category 6a.
Pricing considerations. Later in this article we will address the fact that most data centers are going to Category 6 cabling, but it is important to note that it usually runs at a 30-40% premium over Category 5e; 6A typically runs at a 70% premium over 6. Depending on the size of the cabling project, these premiums can add several thousands of dollars to the cost of the project and may cause the project to exceed budget.
Data center cabling offerings
Data center cabling products are currently offered to meet Telecommunications Industry Association/Electronic Industries Alliance (TIA/EIA) standards for 5e, 6 and 6A requirements. International Organization for Standardization and International Electrotechnical Commission also define cabling standards for Category 7 and 7A, which TIA/EIA does not yet recognize.,/p>
The primary difference among these specifications is the higher bandwidth rating for the cabling system. Greater bandwidth is made possible by using increasingly higher frequencies to carry signal. However, system response at higher frequencies is more susceptible to cross talk and noise interference. Therefore, cable design is distinctly refined to reduce the impact of noise and cross talk at high frequencies.
Manufacturers have many design techniques that allow the cabling system to carry higher bandwidth while circumventing the impact of noise interference.
- Increasing conductor thickness (lowering the gauge of conductor wire)
- Improving the characteristics of conductor insulation
- Using a filler or filament between the pairs to increase their relative distance
- Re-orienting the pairs with respect to each other
- Refining the insulating properties of the jacket
- Increasing the number of twists per inch
- Screening or shielding the individual pairs
- Screening or shielding the collection of pairs
As seen in the list below, these design improvements support higher frequency usage among the consecutive standards.
- Category 5e: 100 MHz
- Category 6: 250 MHz
- Category 6A: 500 MHz
- Category 7: 600 MHz
- Category 7A: 1000 MHz
Category 5e cable is tested to 100 MHz and is suitable for applications of 10Base-T Ethernet, 100Base-T and 1000Base-T (GbE).
Category 6 cable is tested to 250 MHz and is suitable for applications of 10Base-T Ethernet, 100Base-T and 1000Base-T/1000Base-TX (GbE).
Category 6A cable is tested to 500 MHz and is suitable for applications of 10Base-T Ethernet, 100Base-T, 1000Base-T/1000Base-TX (GbE), and 10GBase-T (10 GbE).
Category 7 cable is not commercially available and the TIA/EIA has not yet developed this standard. The specification is expected to support 100G by shielding both the individual pairs and the entire cable to minimize cross talk and system noise.
Data center cabling selection and applications
When it comes to selecting the right data center cabling and matching it to the right application, each primary cabling offering has its benefits and potential drawbacks. Category 5e offers a minimally compliant Gigabit Ethernet solution. Category 5e conductors are typically 24 AWG and less expensive compared with Category 6 and 6A. However, data center applications rarely use 5e because of the inherent performance requirements.
Category 6 cable, on the other hand, is designed to handle voice, video and data simultaneously. Category 6 conductors are typically 23 AWG and well suited for power transmission in PoE applications. Category 6 has 2.5 times the bandwidth, half the attenuation and one-tenth the cross talk of Category 5e cabling.
Since the debut of the Category 6 product, manufacturers have reduced the price relative to Category 5e in order to up-sell users on the higher performing product. Currently, Category 6 cable carries about a 35% price premium over Category 5e. Twice the performance for a 35% premium is an attractive tradeoff for a data center project.
Category 6A tops the performance of Category 5e and Category 6 products by offering 10 Gb speeds. However, it's larger cable diameter blocks air flow and can create cooling issues. The increased size and weight also make it more difficult to install. Low installation volumes mean that manufacturers have not yet been able to lower prices with economies of scale. Category 6A is priced at a 70% premium relative to Category 6. If planning to use 10 Gb network gear, ensure the cabling solution supports the network. If that is the case, price is probably not a critical decision factor.
From our perspective, it is increasingly apparent that Category 6 cable offers the best price/performance. We typically see 6 and 6A installations in our facility, and there is not much 5e installed since 6 has over twice the performance characteristics.
Copper cabling solutions continue to evolve to meet ever-increasing network requirements. Category 5e, Category 6 and Category 6A are three types of cabling solutions currently available, and specification work is under way on Category 7 and beyond. In order to make the best decision for a data center manager's next installation, consider the types of applications that are running, bandwidth needed to run the applications, specified switching infrastructure, port density requirements, space constraints, and finally, overall pricing.
About the author:
John McCreary is general manager of Latisys, a leading provider of colocation, managed hosting, managed services and disaster recovery solutions.
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This was first published in September 2009