Today, data rates of ten Gigabits per second offered by the 10GBASE-T variant of Ethernet may no longer suffice. Largely due the vast uptake of mobile devices, a growing number of users and applications demand higher bandwidth and availability, combined with lower latency. 25 and 40 Gigabits per second are the next milestones on the Ethernet roadmap for copper cabling.
If you are planning to introduce LAN cabling which is to be used for a longer period of time, we recommend that you take the new standards Cat. 8.1, 25GBase-T and 40GBase-T into account when choosing components. Standardization committees have agreed on a quantum leap in transmission performance over twisted-pair copper cabling. This is increasing from 10 to 25 and 40 Gigabit/s, whilst the transmission frequency is increasing to 2000 MHz. However, to be able to handle the inherent attenuation losses and crosstalk, link lengths will have to be shortened. Consultants, installers, end-users and other decision makers need to be forward-looking and take the shorter distances and new options into consideration. For 10GBase-T the distance remains 90 m. With 25 GBase-T, a distance of 50m may well be feasible. With 40GBase-T, this distance will be 24 m.
Cat 8 copper cable allows data centres to introduce cost-effective copper-compatible switches as an alternative to fibre. The cabling standards for both 25GBase-T and 40GBase-T are based on data centre applications, in which servers and switches are usually connected over twisted pair cable. The vast majority of switch-to-server links are shorter than 30m – which has become the maximum channel length in the specification of standards bodies TIA, ISO and IEEE. The 30m maximum channel length consists of 24 metres of horizontal cable and no more than 2 metres of patch cords at either end. Category 8 components set up in this way form a Channel Class I.
To date, 40GBase-T has mainly been considered for applications in the data center area. 25GBase-T could be of interest for the LAN sector, with possible applications in structured office and building automation cabling. Future WLAN access points will require bandwidths higher than 10 Gbit/s. 25GBase-T would make this long awaited evolutionary advance possible.
Backward compatibility
Category 8.1 components are intermateable with the tried and tested RJ45 connector interface for categories 6A, 6 and 5e as specified in ISO/IEC 11801 and EN 50173. However, not all Cat. 8.1 products are interoperable (i.e. working at the required performance level). When evaluating products, planners should check components for full backward compatibility.
The ISO standard for Cat 8.1 require them to be compatible with Cat. 6A or lower. The ISO standard for Cat 8.2 doesn’t require the installation to be backwards compatible with Cat 7A, Cat 7, Cat 6A and below.
Recommendation for Cat.8.1 installations: Two measurements for formal acceptance should take place after installation, one for Cat. 8.1 and one for Cat. 6A.
It is also important to point out that Category 8.2 connector interfaces are not backward compatible with the RJ45 jacks of existing cabling. Although Cat 8.2 systems and connectors should make the most of the installed cabling from the outset, there are no switches and servers that are equipped with the same connector interface. The Cat. 8.2 connector systems require comparatively expensive, cumbersome adapter cables and do not offer any advantages in terms of transmission speed.
Conclusion:
Cat.8 will cover the next evolutionary step in copper Ethernet connectivity. It can provide the headroom in transmission speed to future-proof installations both in DC and LAN environments. Cat. 8.1 can be easily integrated into existing RJ45 environments without compatibility issues and offers the same speed advantage as Cat.8.2.
