CATEGORY 6 & 7: A Point of Information

Historically, information transmission rates double every 18 to 24 months. To support this growth, in September of 1997, ISO began formalizing performance criteria for cabling systems designed to support positive power sum attenuation-to-crosstalk (PSACR) values to 200 MHz (category 6/class E) and 600 MHz (category 7/class F). At the time, TIA also recognized the urgent demand for a high bandwidth unshielded twisted-pair cabling solution and began concurrent development on category 6. Although TIA has not initiated development of a category 7 solution, there is significant harmonization between the status of the TIA category 6 and ISO class E draft Standards.

It is interesting to note that although the positive PSACR frequency for category 6/class E cabling systems is 200 MHz, due to considerations such as equipment crosstalk cancellation capability, both TIA and ISO will be characterizing these cabling systems to 250 MHz. At this time, ISO class F is characterized to an upper frequency value of 600 MHz.

In conjunction with the cabling objectives outlined in 1997, TIA and ISO have implemented provisions into their draft Standards to ensure that category 6/class E and category 7/class F cabling systems will work in harmony with existing generic infrastructures. To achieve this, systems and components are required to be backward compatible with existing categories and classes, as well as be interoperable with components of like categories from different manufacturers. TIA has since devised a test method that provides a benchmark against which active equipment and systems manufacturers can qualify their category 6 plugs and sockets. Compliance to the provisions ensures component interoperability and backward compatibility. Work on category 7 plug and socket requirements is still pending the final outcome of the ISO/IEC category 7 connecting hardware interface selection process.

The significant differentiator between category 6/class E and category 7/class F is the cabling media. Category 6/class E is generally considered to represent the highest bandwidth capable of being supported by unshielded twisted-pair (UTP) and screened twisted-pair (ScTP) cables; to achieve even greater performance, category 7 cables must utilize a more robust, full shielded construction which virtually eliminates crosstalk between all pairs up to 600 MHz. The construction of the category 7/class F media offers some significant performance advantages, particularly with respect to crosstalk, over category 6/class E cabling.

At this time, the channel and permanent link performance values for category 6/class E and category 7/class F are firm and unlikely to undergo significant revisions. The released TIA and ISO Standards are also expected to specify laboratory test and field verification methods, installation practices, and other considerations such as reliability and durability in addition to transmission performance. The few remaining items that need to be addressed prior to standard publication are generally related to these topics.