Category 7 and Category 7A

There is much discussion about the feasibility of implementing structured cabling systems with Category 7 or Category 7A cables and components (ISO 11801). For example, the organization's technology projections, such as 40-Gigabit Ethernet or 100-Gigabit Ethernet, are evaluated, along with the costs this implementation would entail for the MACs, etc.

To further illustrate this current topic, I am transcribing an article from a specialized magazine, which I hope will help give you more tools to make a decision in future projects.

Care must be taken in the design of these types of interconnections, since the possibilities of copper support for very high-speed applications (40Gbit / 100Gbit) are being studied in the standardization committees; it must be taken into account that currently they will be used for applications of 10 Gigabit Ethernet at most.

ISO/IEC 11801 Adm2

This standard defines the components, permanent link, and channel (Adm.1) of class EA/FA for a cabling system up to 10 Gbps. The most important differences from the corresponding EIA/TIA standards are:

• The channel is designed for 10GB/s applications of the EA class and therefore its components have higher performance than the Cat. 6A channel and the Cat. 6A components of EIA/TIA.
• Shielded technology is fully implemented.
• Classes F and FA and their components Cat.7 and Cat. 7A are defined.

Cat. 7 Connectivity

In the ISO/IEC 11801 standard, Class F with Cat. 7 is defined up to 600MHz. For Cat. 7 connectivity, two types of connectivity have been defined: IEC 60603-7-7 (GG45) and IEC 61076-3-104 (Tera).

Under current standards, the difference between class F and class EA (Cat. 7 / Cat. 6A components) is very small (600MHz vs. 500MHz), thus Cat. 7 is not expected to evolve in the future.

In any case, Class F (Cat. 7) does not specify external crosstalk (ANEXT) as required for 10GbE applications and specified in Class EA. The ISO/IEC 24750 standard (testing and migrating a Class E/F installation to 10GbE) assumes that Class F meets the external crosstalk requirement, but this is merely an assumption and not a definition. Therefore, it is questionable whether Cat. 7 can be used as such for an installation ready for 10GbEthernet support.

Cat. 7A Connectivity

The same connector types for Cat7A as for Cat7 have been defined in ISO/IEC 11801 ed. 2.1 Adm. 2

Since the definition for IEC 60603-7-7 is not suitable for 1000MHz, a new standard, IEC 60603-7-71, has been defined for GG45 Cat. 7A. Like the old one, this is backward compatible with RJ45 and behaves the same as an RJ45 if this format is attached to the module; however, when operating as an RJ45, its actual performance is Cat6A.

GG45 pin assignment (source ISO/IEC JTC1/25N1513)

Therefore, the connector can switch the regular upper pins 3, 4, 5, and 6 to additional pairs 6', 7' and 4', 5' in the lower area. The goal of Cat.7 was to achieve better NEXT connectivity. By switching the 6/7 and 4/5 pairs to the lower side, a greater distance to the other pair has been achieved, which provides better NEXT performance.

The major unknown in this combination is the mechanical switch that toggles between the upper and lower pairs. The GG45 connector automatically operates the switch if it is busy. To achieve a lifespan of 750 power-on/power-off cycles for this type of system, it must be hermetically sealed, but this results in very high costs and extreme electrical performance problems. Furthermore, the mechanical switch implemented for Cat7 has shown a tendency to fail.

Tera

Tera is defined in IEC 61076-3-104 where they were revised in 2006 with respect to Cat. 7A.

Tera pin assignment (source ISO/IEC JTC1/25N1513)

Since it is based on a fully protected 4-camera system, the enhanced Cat. 7 NEXT requirement can be easily achieved, however, of course at the price of no backward compatibility.

Cat. 6A versus Cat. 7A

Investing in a more expansive technology only makes sense if it can achieve better QoS (greater resistance to disturbances, higher availability, higher performance, etc.) for the running application or a longer lifespan for the investment (future-proofing). In the case of cabling, it's quite obvious that Cat. 7 or Cat. 7A offers better common-mode rejection, crosstalk, NEXT, etc., which can justify a larger investment. This is different in the case of connectivity. (Article published in Datacenter Dynamics on June 10, 2011)