Next-gen copper cabling systems

Today’s servers are shipping with 10 Gbps copper ports while power consumption and heat dissipation have been reduced to acceptable levels. As global demand for higher speed and additional data bandwidth continues unabated, the IEEE and some cabling groups have started a project called ‘Next Generation Ethernet’, or in simple terms - 40 Gbps over copper.

Remember the endless discussions and development steps for 10 Gbps over copper? There have been heated debates about whether or not we need it, how it works, power consumption, heat dissipation and the UTP v STP discussion. Now, that’s all resolved and working well. The cabling industry has developed two new cabling classes, EA and FA, and the acceptance of shielded systems has increased significantly.

Figure 1: Evolution of ethernet standards.

Latest IEEE and ISO/IEC updates

IEEE and ISO/IEC recently held meetings and announced a first technical framework. Their proposals assume frequencies between 1200 and 2000 MHz, resulting in the following considerations: higher frequencies allowing for easier coding; the higher the frequency, the higher the attenuation; greater length results in lower frequencies; the length is reduced to a 30 m channel.

The cabling standard working groups are considering two scenarios: the first is called Class I or Cat 8.1 (depending on the standards body) based on Category 6_A style components; and the second is Class II or Cat 8.2, based on Category 7_A style components. Both scenarios extend requirements up to 2 GHz, with the latter being the more demanding. Both include the internal layout of the active equipment for channel modelling: taking the influence of the internal elements of the active equipment (magnetics, track layout, etc) into consideration in the cabling model. Doing so during the requirements definition stage will help with signal integrity requirements and consequently reduce power consumption for data post-processing.

No doubt many will be tricked into thinking that Cat 8 has better performance than Cat 7_A, when in fact the opposite is true. Proof that Cat 7_A has higher NEXT (near-end crosstalk) performance is shown in the following graphic. The TIA proposal for Cat 8 is an extrapolation of Cat 6_A values and in fact yields much lower performance than Class FA systems. The difference at 1000 MHz for NEXT is 10 dB better than the proposed Cat 8.

To remove some of the confusion, ISO/IEC was forced to reconsider their naming system.

Figure 2: NEXT proposals.

This resulted in the current new terminology: Category 8.1 (RJ45 based) and an extrapolation of Cat 6_A values; Category 8.2 (Category 7A based) and an extrapolation of Cat 7A values.

The development of Cat 8.1 product/systems represents serious challenge, with the biggest issue being the RJ45 connector. However, 8.2 systems will meet all current requirements and expectations of IEEE as power consumption is one of the key design considerations.

In addition, ISO/IEC JTC1/SC25 WG3 instructed a project team to investigate the feasibility of 40 Gbps on existing cabling classes. This team is expected to launch a report with the title ISO/IEC 11801-99-1 ‘Guidance for balanced pair cabling in support of at least 40 Gb/s data transmission’ in mid-2014. The report will include information on how to run 40 Gbps over existing cabling classes. The findings are distinctive: only Class FA systems are capable of supporting 40Gbase-T; Class EA systems will not be able to do so owing to electrical limits. The second group is investigating and proposing technical details for the two new projected cabling classes, 8.1 and 8.2.

Currently it is difficult to foresee which one will become the main ‘standard for the future’. Logically, technically and economically it would be the 8.2 standard. However, the past has shown that the more obvious standard is not necessarily always the successful one.

In fact, today’s high-end Class FA systems with a respectable margin over current Class FA limits will meet the requirements for Cat 8.2. One reason discussed behind the scenes is the consideration that a higher performing cable provides more futureproofing abilities. Class FA systems and current Class 8.2 systems are based on S/FTP cable with superior cross-talk performance and the highest available bandwidth on the market. Proposed 8.1 systems would use F/UTP with a lower bandwidth and lower crosstalk capabilities.

Another driver is the connector preference. The RJ45, of course, has been the standard connector for more than a decade, and customers prefer backwards compatibility. This is why current 8.1 proposals use the RJ45 connector.

Cat 8.2 systems use different concepts, usually chamber designs with a connector performance of 1500 MHz and above. Even here, backwards compatibility is supplied by hybrid patch cords. This is the usual way in the fibre-optic world.

Figure 3 shows how it works. Today’s configuration for 1 and 10 Gbps would be Cat 7A connectivity with a hybrid patch cord (eg, TERA to RJ45). A change to a full 8.2 system performance can be achieved simply by changing the patch cords at both ends.

Figure 3: Backwards compatibility and upgrade path.

The superior design of the four-chamber connector allows the operation of much higher frequencies than the backwards-compatible IEC 60603-7-71 (RJ45) interface. This results in some design advantages as well as futureproofing for next-generation services. As the intended application is an end of row (EoR) or middle of row (MoR) for data centres, the practical scenario is shown in Figure 4.

Figure 4: Upgrade in an EoR scenario via patch cords.

As mentioned, a simple change of patch cords is needed for any 40 Gbps system, either RJ45 or any other interface. This is the same as with 10 Gbps and Class EA. In order to upgrade from 1 to 10 Gbps the patch cords must be changed to Cat 6A patch cords.

The fibre-versus-copper questions usually arise with any new application. In the past 15 years the outcome has always been the same, a mixture of both where the ratio may change slightly.

A similar outcome is to be expected for 40 Gbps as both media types have pros and cons and customer requirements, even in the data centre area, differ.

Field testing

During the last IEEE meetings, some vendors showed field testing devices with a capability of 2000 MHz and above. A principal feasibility has been demonstrated and should not represent a barrier for the 40 Gbps implementation. All the capabilities shown have been based on Class FA systems. Various test companies have shown and demonstrated capable testers out to 2000 MHz, and others will soon follow.

Conclusion

Class FA systems (ISO Category 8.2) have the highest capability while requiring the lowest levels of complexity. It is the only performance class on the market that is available, reliable and fully backwards compatible with all other existing cabling classes. An upgrade can be achieved easily with a simple patch cord change. The other path (Cat 8.1) is unknown and still uncertain.

Further steps and developments will be needed to use RJ45 technology at such high frequencies. Be cautious about claims around the TIA and ISO/IEC names and definitions, they are misleading and confusing at this point in time.

Customers should trust the technical reality that there is no substitute for bandwidth, except more bandwidth. A decision to invest in the highest performance class will result simply in the longest and most reliable cabling infrastructure lifetime.