Short Guide to Twisted-pair Cabling Categories

Short Guide to Twisted-pair Cabling Categories
Twisted-pair 100-Ohm horizontal cables and connecting hardware are designed to be “transmission lines”. When they are interconnected and present a “cabling channel”, their main purpose is to transmit signals from the transmitter to receiver successfully.

When the signal propagates along a cabling system, it loses power and is deformed by external and internal noise. To ensure that the receiver decodes the signals successfully, it is needed to “characterize” maximum allowable degradation for cabling channels and components within a specific frequency range. Defining and standardizing several performance “Categories” serves this purpose.

Each “Category” is a set of transmission parameters defining maximum allowable degradation and specified up to a defined frequency. Lower Categories will more degrade the signal and have less bandwidth.

The most important are the following Categories: Category 3, Category 5, Enhanced Category 5 (5E), Category 6 and Category 7.

The Categories are specified in ANSI/TIA/EIA-568-A and ANSI/TIA/EIA-568-A-5 standards:

* Category 3 cables, components and channels are specified up to 16 MHz. This Category is approved and specified in ANSI/TIA/EIA-568-A. Category 3 channels support voice applications and 10Base-T.

* Category 5 cables, components and channels are specified up to 100 MHz. This Category is approved and specified in ANSI/TIA/EIA-568-A. Category 5 channels support voice applications, 10Base-T, 100Base-T and 1000Base-T (Gigabit Ethernet) with additional testing.

* Category 5E cables, components and channels are specified up to 100 MHz. Category 5E has the same frequency range as Category 5, but specifies additional transmission parameters for bi-directional multi-pair transmission used in 1000Base-T. This Category is approved and specified in ANSI/TIA/EIA-568-A-5. Category 5E channels support voice applications, 10Base-T, 100Base-T and 1000Base-T (Gigabit Ethernet).

* Category 6 cables, components and channels are specified up to 250 MHz. Category 6 standard is not yet approved (approval expected in 2001). Category 6 channels support all existing applications supported by Category 3, 5 and 5E and will support future applications.

* Category 7 cables, components and channels are specified up to 600 MHz. Category 7 standard is not yet approved. At this time, the future of Category 7 is unclear. Some industry experts think that installing fiber to the desk (FTTD) will be less expensive than installing Category 7 solutions.

To minimize confusion and maintaining adequate transmission performance, it is recommended installing cables and components of the same Category. For example, install Category 5 cable with Category 5 connecting hardware and patch cords.

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