A key standards body working on standards for structured wiring systems is the TIA’s TR-42 committee, with its various sub-committees and working groups. The resulting standards are published as TIA-568. There have been numerous addenda and revisions since the first 568 standard publication in 1991. The latest, as of 2015, is referred to as revision D.
The US has an umbrella organization, ANSI, that sanctions standards in many industries. Thus, the American standard for building writing is often referred to as ANS / TIA 568-D.
The corresponding standard for Europe and other regions is the IEC 11801. IEC standards are sanctioned by the ISO, hence the name ISO / IEC 11801. This standard also has updates as well as variants for different types of buildings, such as residential, office, industrial, etc. The latest version for office buildings is ISO / IEC 11801-2:2017.
The TIA/EIA 568 standard that governs structured cabling systems for communication networks specifies the pinouts and spacing of the four-pair category cables. The connector specification is referred to as 8P8C – “eight position eight contact.” The well-known RJ45 “registered jack” technology is a version of 8P8C connectors, but the terms “8P8C” and “RJ45” are not strictly synonymous. The RJ45 plug’s molded body contains an alignment key not specified in the TIA 568 standards.
In practice, however, the equipment and connector manufacturers generally refer to their TIA-568-compliant 8P8C connectors informally as RJ45s, and this name has become widespread. More importantly, the TIA-568 network cables and equipment used in PoE and PoH systems have full compatibility and intermateability.
For the purposes of PoE product compatibility, the connector interface is identical to that specified in the TIA 568 cabling standards. Category cables used in standard PoE systems can work with equipment and devices made by any manufacturer, in any country. The PoE switches and devices have been developed to simplify installation in terms of physical-layer interconnection, as well as in the upper layers that manage the power levels. Some equipment manufacturers describe the products as “plug and play,” and many, such as web cameras, can readily be installed by consumers.
The various categories have different bandwidth capabilities, resulting from the cable’s design. The main design features aim to reduce electromagnetic interference from external sources and to reduce cross talk from other wires in the same cable. The design variables affecting bandwidth include insulation materials, use of shielding, type of shielding, and twist characteristics – the number of twists per meter.
The higher the cable type or “category” number, the higher the bandwidth performance. Because bandwidth and distance trade-off against each other, the higher-performing cables generally are specified for higher bit rates over a commonly used distance of 100 meters. In some cases, the higher-performing cables are specified with options for bit rates and distance, or a combination of higher bit rates and longer reach.
Low-speed versions of unshielded twisted-pair cable have been used over many decades for internal telephone wiring. Versions rated at 1 and 4 MHz are sometimes referred to as Cat-1 and Cat-2, but these names are not defined in ANSI / TIA standards. Anixter has used a “Level” numbering scheme with 1 and 2 for these products. These cables often were called “telephone wire” or “station wire.” Categories 3 through 7a are defined in ISO / IEC standards and ANSI / TIA standards. Categories 3 through 5e were unshielded, and the standards defined Cat-6 with both shielded and unshielded versions.
Early local-area-network (LAN) installations, dating back to the 1970s and early 1980s used coaxial cable. One early IBM LAN used shielded twisted pair. In the mid-1980s, 16-MHz unshielded twisted pair, later known as Category-3, was used for a 1 Mbps LANs. Cat-3 UTP also was first used for in-line power, starting in the mid-to-late 1990s, for early VoIP systems.
As the technology has progressed, Cat-3, Cat-4, and Cat-5 cable types have become obsolete. That is, they no longer are in production. Cat-5e cable is still in production, but its use is being superseded by Cat-6 and Cat-6a. Systems operating with Cat-3 or Cat-5 cable, of course, can continue to operate. The owners or operators can use higher rate cables for any maintenance, extensions, additions, etc.
The general trend since the 1990s has been for computer users to need more network bandwidth as processors, memory, software, displays, printers, storage systems, and other technologies have improved. Computer files became larger, and users needed transmission faster rates. The IEEE 802.3 sub-committees are continually working on standards addenda or on new versions. The standards organizations involved in physical-layer networking are also working on new cable specifications to keep up with requirements for faster bit rates. There is also a change in the mix of cable types being sold as the networking standards and transmission rates scale up.
In the 1990s, Cat-5e cable had the largest share of the premises cable market. This was superseded by Cat-6, which was developed in the late 1990s and widely deployed in the last 15 years. Cat-6 sales have levelled off, and Cat-6a, which was developed to support 10-Gbps networking, is showing stronger market acceptance.
Cat-7 and Cat7A are not covered in the TIA standards that are mainly used in the US. These two cable types are recognized in the ISO / IEC standards used outside the US. Cat-7 and Cat-7A cables cannot use the same “RJ45” connector as lower-rate category cables. The Cat-7 and Cat-7A cables require a special shielded 8P8C connect with additional contacts. As a result, Cat-7 and Cat-7A cables are mainly serving smaller market niches as of 2017.
What is the status of Cat-8 in standards committees? The TIA standards group moved from Cat-6a to Cat-8, essentially ignoring Cat-7 and Cat-7A due to the connector and bandwidth issues. In July of 2016, the TIA released document TIA-568-C.2-1, which specifies minimum requirements for shielded Cat-8 cable and components, including connectors, connecting hardware, and equipment cords. The TIA also will incorporate the Cat-8 specifications into the updated TIA-568-D standard.
The IEEE 802.3bq standard was completed in September 2016. It specifies 25GBaseT and 40GBaseT (25 Gbps and 40 Gbps) transmission over 30 meters of Cat-8 cable. The standard is mainly focused on shorter runs inside data centers, so the 30-meter specification includes a 24-meter link and 6 meters of patch cords.
Although the standards groups have published standards with Cat-8 cable and with 25GBaseT and 40GBaseT transmission, the equipment manufacturers are still in development phases. Equipment products using 8G are not expected to be widely available until 2019, so adoption of Cat-8 cable is not expected to ramp up until 2020. Although the standards specify compatible connectors, it is not clear whether this cable type will be used with PoE equipment. With its design focused on short spans in data centers, Cat 8 probably is not cost-effective for PoE.
There are countless magazine articles, web publications, and conference presentations about the relative merits of different cable types for different datacom applications. The three main factors for deciding among cable types are bit rate, distance, and cost. Several other factors indirectly are related to cost: energy and cooling requirements, energy efficiency, density, availability of space in ducts, trays, and rack hardware, etc. In addition, less readily quantified factors come up, such as customer preference or comfort and expectations as to when system upgrades will be needed.
In the data center market, fiber may be capturing a larger share of the overall cable demand due to its distance and bit-rate capabilities. Fiber is clearly advantageous in the very large “hyper-scale” data centers. Gigabit-rate copper links, using Cat 6A and higher-rate cables will have a strong niche in shorter inside spans, such as links at the end of rows, links at the middle of rows, such as on the top of the racks. Within the data center market, the more interesting segment for copper cables may be smaller localized data centers. As of 2017, it is not clear whether data centers will be a high-growth application for copper cabling.
The bright spot in the copper datacom cable market outlook, however, may prove to be premises applications that will take advantage of PoE or PoH technologies. Fiber cable is not a factor in these applications. Also, for many PoE applications, such as IP telephones, LED lighting, web cameras, and building controls, gigabit transfer rates are not the deciding factor among cable types. Thus, PoE and PoH could prove to be key market drivers for Cat-6 and Cat 6A cable sales in the coming years. Plus, the attractiveness of efficient, easily managed power delivery may prove attractive with some of the emerging Internet of Things (IoT) applications – operating sensors and cameras, collecting data, running point-of-sale terminals, signs and information displays in public places.
For structured cabling in other building and campuses, fiber’s role is more likely to be identified with backbone installations, not horizontal runs or connections to individual devices. To the extent that many of these devices may benefit from PoE, campus and building networks might also offer better growth prospects for TWP cable now that PoE technologies are proliferating and maturing.