Article by Benson Mmari
Cabling systems are categorized in terms of the data rates that they can sustain effectively. The specifications describe the cable material as well as the types of connectors and junction blocks to be used in order to conform to a category.
Cabling systems are categorized in terms of the data rates that they can sustain effectively. The specifications describe the cable material as well as the types of connectors and junction blocks to be used in order to conform to a category.
For ISO/IEC standards, the category refers to the cable and class refers to the connector. ISO are international standards and can be followed anywhere in the world. A standard is different than a code in that standards are voluntary and provide a guideline so that all manufacturers have a minimum set of parameters to work with. A code, on the other hand, is law and is enforced through an AHJ (Authority having Jurisdiction).
Longer connections for Gigabit Ethernet use optical fiber, the goal is to leverage the CAT 5 and CAT 5E twisted-pair wiring most organizations already have in place for connections out to the desktop. (Four pairs of twisted pair are used.) In old split pair configurations, PoE MidSpan cannot be used. PoE is supported on 5e or better; however the higher performing cable provides better heat performance with shielded systems better than UTP.
THE IEEE STANDARDS
The Institute of Electrical and Electronics Engineers (IEEE) standards association ratified several versions of the technology. The first two early designs were StarLAN, standardized in 1986, at one megabit per second,[6] and LattisNet, developed in January 1987, at 10 megabit per second.[7][8] Both were developed before the 10BASE-T standard (published in 1990 as IEEE 802.3i) and used different signalling, so they were not directly compatible with it.[9]
In 1988 AT&T released StarLAN 10, named for working at 10 Mbit/s.[10] The StarLAN 10 signalling was used as the basis of 10BASE-T, with the addition of "link beat" to quickly indicate connection status. (A number of network interface cards at the time could work with either StarLAN 10 or 10BASE-T, by switching link beat on or off.[11])
Using twisted pair cabling, in a star topology, for Ethernet addressed several weaknesses of the previous standards:
· Twisted pair cables could be used more generally and were already present in many office buildings, lowering overall cost.
· The centralized star topology was a more common approach to cabling than the bus in earlier standards and easier to manage.
· Using point-to-point links instead of a shared bus greatly simplified troubleshooting and was less prone to failure.
· Exchanging cheap repeater hubs for more advanced switching hubs provided a viable upgrade path.
· Mixing different speeds in a single network became possible with the arrival of Fast Ethernet.
CATEGORIES OF IEEE TWISTED PAIR CABLES
The two most widely-installed categories of IEEE twisted pair are CAT 3 (voice) and CAT 5e, traditionally, however with new installations; category 5e for voice and one high speed to support 10GBASE-T for long term usage are the most common. According to a BSRIA study, 78% of all new installations are shielded. While the two cables may look identical, CAT 3 is tested to a lower set of specifications and can cause transmission errors if pushed to faster speeds. CAT 3 cabling is near-end crosstalk-certified for only a 16 MHz signal, while CAT 5 cable must pass a 100 MHz test. CAT 5E replaced CAT 5 in both standards groups.
The CAT 6 specification, published in 2002 (the same time as ISO Category 7/class F), improves on CAT 5E in terms of near-end crosstalk, balance, and bandwidth. According to IEEE, 70% of new installs in 2004 were CAT 6.
Category 7/Class F (ISO/IEC), published in 2002, is a fully shielded system. The shielding provides superior noise immunity and performance. Until February 2008, it was the only published standard to support 10GBASE-T to a full 100m.
CAT 7A/Class FA and Category 6A/Class EA specifications were published in February 2008.
The IEEE standards categories
Category | Maximum data rate | Usual application |
CAT 1 (de facto name, never a standard) | ||
CAT 2(de facto name, never a standard) | 4 Mbps | |
CAT 3 | 16 Mbps | |
CAT 4 | 20 Mbps | Used in 16 Mbps Token Ring, otherwise not used much. Was only a standard briefly and never widely installed. |
CAT 5 | 100 MHz | 100 Mbps TPDDI 155 Mbps ATM No longer supported; replaced by 5E. 10/100BASE-T 4/16MBps Token Ring Analog Voice |
CAT 5E | 100 MHz | |
CAT 6 | ||
CAT 6E | Support for 10 Gigabit Ethernet (10GBASE-T) May be either shielded (STP, ScTP, S/FTP) or unshielded (UTP) This standard published in Feb. 2008. Minimum for Data Centers in ISO data center standard. | |
CAT 7 (ISO Class F) | Full-motion video Teleradiology Government and manufacturing environments Fully Shielded (S/FTP) system using non-RJ45 connectors but backwards compatible with hybrid cords. Until February 2008, the only standard (published in 2002) to support 10GBASE-T for a full 100m. |
