Category 8 questions answered
As the Telecommunications Industry Association (TIA) TR-42.7 sub-committee works diligently toward finalising the specifications for Category 8 twisted-pair cabling systems, we asked several members of the subcommittee to answer some questions about Cat 8.
Q: Can you provide a summary of how a Cat 8 cabling system’s capabilities compare to those of previous-generation twisted-pair cabling systems, such as Cat 6, 6A, 7, 7A, etc? (Please address bandwidth, channel configuration and channel distance, as well as other performance characteristics you deem appropriate. Please describe how, if at all, the TIA is approaching backward compatibility between Cat 8 and previous-generation twisted-pair systems.)
Answer provided by Leviton Network Solutions senior product manager Mark Dearing:
Since Cat 5e was introduced in 1999, one of the constants in structured cabling has been the 100m, four-connector channel. As data rates have increased, one of the primary differences between category systems is the frequency at which the signal is transmitted over the cable.
Cat 7/7A offers a 100m four-connector channel using shielded cabling and has been designed to transmit signals at a frequency of 1,000MHz. Even though Cat 7/7A operates at the higher frequency, there is no corresponding improvement in data rate over Cat 6A because 10GBase-T is still the fastest twisted-pair-based data rate recognised by IEEE 802.3. Therefore, even if a Cat 7/7A cabling system is installed, any available active equipment would be limited to 10Gbps performance. Cat 7/7A is not a recognised category by TIA.
Cat 8 is a significant departure from previous systems in that it uses a frequency of 2,000MHz, and is limited to a 30m two-connector channel. Unlike Cat 5e through Cat 6A, which could use either unshielded twisted-pair (UTP) or shielded cable construction, Cat 8 will require shielded cabling. The most likely cable construction for Cat 8 will be 22-AWG S/FTP cabling.
Cat 8 is also unique in that the International Organisation for Standardisation (ISO) standard will recognise two different classes of product. (This topic is covered in greater detail later in this article.) Class I is based on the traditional RJ45 connector, while Class II will accept non-RJ45 connectors similar to Cat 7/7A. While both solutions will offer backward compatibility in terms of transmitting the lower category data rates (1G or 10G), the Class I solution offers a migration path using the RJ45 connector platform. For example, a customer might install a Cat 8 jack-to-jack link now, but continue to use Cat 6A patch cords until the active equipment is upgraded. While the ISO standard includes both classes, the TIA Cat 8 standard will only recognise a Class I solution.
Q: Given Cat 8’s capabilities, where and how is it most likely to be deployed (e.g. in a data centre vs. a corporate LAN, top-of-rack vs. end-of-row architectures)?
Answer provided by CommScope engineering senior principal Masood Shariff:
Cat 8 cabling is designed to support emerging IEEE 25GBase-T and 40GBase-T needed as server-to-access-switch interconnect applications. This need has been identified and available, or under development, over optical fibre links for longer reach (up to 500m), or twinax links for short reach (up to 7m).
The opportunity for balanced twisted-pair as a cost-effective viable media option for the intermediate distance needs between 5m and 30m, sufficient to serve 20 cabinets or racks in a data centre, led to the initiation and development of both the IEEE 802.3 application standards and the associated TIA as well as ISO/IEC Cat 8 cabling standards.
Q: What communication or collaboration is taking place between the TIA and the IEEE-particularly the 802.3bq Task Force-to ensure the TIA’s Cat 8 specifications are in concert with the IEEE’s 40GBase-T and 25GBase-T specifications?
Answer provided by Masood Shariff:
The IEEE 802.3bq Task Force is collaborating with TIA TR-42.7 and ISO/IEC/JTC 1/SC 25/WG3 to ensure consistency and compatibility of the cabling specifications within the ‘link segment’ specifications in IEEE 802.3bq applications. Liaison letters to clarify requirements or provide additional information are generated at most meetings and latest drafts of the TIA and ISO Cat 8 specifications are sent to the IEEE 802.3bq committee, where they are posted in a ‘private’, password-protected area for members to review and comment. The relationship between IEEE 802.3bq and its companion cabling standards organisations has been very positive and constructive, with several common members attending the meetings.
Q: Can you explain the relationship between the TIA and ISO/IEC groups working to define Cat 8 cabling specifications? Specifically, how are the two groups’ efforts similar and how do they differ from each other? Observers of the standards-creation processes see terms like ‘Class II’, ‘Cat 8.1’, and ‘Cat 8.2’. The meanings of these terms are not necessarily self-evident.
Answer provided by Siemon director of standards and technology Valerie Maguire:
The TIA TR-42 Telecommunications Cabling Systems Engineering Committee and the joint technical committee of the International Organisation for Standardisation and the International Electrotechnical Commission (ISO/IEC JTC 1) share similar missions of developing, maintaining, and promoting standards related to information and communications technology. However, while TIA standards represent the consensus positions of their North American corporate constituents, ISO/IEC JTC1 standards represent the consensus positions of their member countries.
As a result, voting within these organisations is also different, with TIA recognising one vote per member company and ISO/IEC recognising one vote per member country. A voting practice that accommodates regional preferences is the key reason why there are additional shielded options, such as Cat 7A/Class FA specified in ISO/IEC standards compared to TIA standards.
While specifications for same-bandwidth balanced twisted-pair copper cabling systems are well harmonised between TIA and ISO/IEC, there are a few differences that stand out-most notably the naming convention for these cabling systems. In ISO/IEC standards, structured cabling components (e.g. cables, connecting hardware, and patch cords) are characterised by a performance “category” and are mated to form a permanent link or channel that is described by a performance “class.” In TIA standards, components and cabling are both characterised by a performance “category.” ISO/IEC and TIA equivalent grades of cabling, arranged in order of increasingly more stringent transmission performance, are shown in the table.
Note that, although ISO/IEC Class I and TIA Cat 8 cabling systems are specified to 2,000MHz, they will not be electrical supersets (i.e. exhibit superior performance) of ISO/IEC Class FA cabling up to 1,000MHz.
Both the ISO/IEC JTC1 and TIA TR-42 are developing requirements for the balanced twisted-pair media that will support the 25GBase-T and 40GBase-T applications that are currently under development by IEEE 802.3. ISO/IEC is developing requirements for Class I cabling constructed from Cat 8.1 components, and Class II cabling constructed from Cat 8.2 components. TIA is developing requirements for Cat 8 cabling constructed from Cat 8 components and is also undertaking an initiative to develop Class II cabling requirements that will harmonise with ISO/IEC. Class I and Cat 8 cabling specifications support modular RJ45-style connectors. The performance associated with Class II cabling can only be realised when Cat 8.2 cables are used in conjunction with non-RJ45 interfaces such as the Siemon TERA connector. Draft ISO/IEC Class I and II, and TIA Cat 8 cabling specifications, are mature and currently circulating for industry comment and review.
Note that Class I, Class II, and Cat 8 cabling is characterised to 2GHz and intended to support 30m cabling channels that contain no more than two connectors. These channels and the emerging 25/40GBase-T applications that they support are specifically targeted for deployment at the data centre “edge,” where server-to-switch connections are made. Data centre designers who can arrange their rack and cabinet layouts to support maximum 30m channel connections at these locations today will be well-positioned to migrate to 25/40GBase-T when the technology becomes available.
Q: What steps can a customer take today to design their facilities in such a way that they are “future-ready” to install Cat 8 when product becomes available?
Answer provided by Panduit product development manager Frank Straka:
Cat 8 is a 30m channel, comprising a 24m permanent link and up to 6m of patch cable. Therefore, when planning data centres with end-of-row or middle-of-row topologies, ensure that your jack-to-jack links are no more than 24m in length and that you do not need more than 6m of patch cords in total. What this means for patching is you could have two, 3m patch cords, a 1m and a 5m patch cord, or any combination that adds up to 6m or less.
For top-of-rack topologies, the 3m reach should be more than sufficient to cover any direct switch-to-server links, especially if the data centre had been using technologies like SFP+ that have a reach limit of about 5m.
Q: How similar can we expect Cat 8 products to be compared to jacks and plugs existing in the market today? Will products be field-terminable? And with Cat 8 being a shielded technology, are there any anticipated concerns for installers?
Answer provided by Frank Straka:
Cat 8 products are anticipated to be significant upgrades over existing Cat 6A products due to the four-times increase in bandwidth. However, these upgrades will primarily occur internally to the jack and plug in order to meet that bandwidth. Externally, they will be about the same form and fit as prior category jacks. This makes sense, as they need to work with the same patch panels, switches, and other equipment with which users are familiar today.
Cat 8 will be field-terminable. Now given that Cat 8 is shielded, field-terminable, and with a very high bandwidth, expect there to be at least some improvements made to how jacks are terminated in the field to both meet this new bandwidth and to ensure a good bond with the shield. For many contractors, the biggest change will be going into a shielded system and ensuring that the cable is properly grounded. If we connector companies do our job right, grounding the Cat 8 cables and connectors will be a seamless process for the installer.
This article originally appeared in Cabling Installation & Maintenance. Reproduced with permission.