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link class

All cabling standards and draft standards, ISO/IEC 11801, EIA/TIA 568 and EN 50173, use classification systems for specifying the transmission path. One speaks of link classes for end-to-end connections. ISO/IEC 11801 recognizes the classes "A", "B", "C" and "D" for TP cables. In addition, the DIN draft 44312-5 for the link classes "E" and "F" was adopted in ISO/IEC 11801, as were the link classes "EA","FA" and "G", which were added later.

A link class specifies the transmission behavior for the complete transmission path up to the telecommunications connection box.

The link specifications include all transmission media, connector elements, patch panels and the junction box. The workstation cabling is deliberately left out of the specification because some telecommunications end devices are supplied directly with the connecting cable, but there is also the possibility of uncontrolled replacement of connecting cables, which would affect the specifications.

Definition of Link, Permanent Link and Channel

Definition of Link, Permanent Link and Channel

Link classes for applications up to 10 Gigabit Ethernet

Class A: Applications with low data rates and frequencies up to 100 kHz. This class is suitable for X.21/V.11, basicISDN, for example.

Class B: Voice applications with frequencies up to 1 MHz, e.g. for basic and primary multiplex connection of ISDN.

Class C: Voice and data transmission with frequencies up to 16 MHz. This class can be used for 10Base-T, for Token Ring 4/16 Mbit/s or PBX technology. Link classes "A", "B" and "C" are no longer considered in the newer standards.

Class D: Voice and data transmission with frequencies up to 100 MHz. Used in Fast Ethernet, TPDDI.

Class E: Voice and data transmission and multimedia with frequencies up to 250 MHz, including ATM 155 and 1000Base-T. Class E allows the use of high-quality overall shielded S/UTP cables or preferably four-pair S/STP cables. With regard to the connection technology, improved RJ45 plugs and sockets are used.

Class EA: The link class "EA" has a transmission bandwidth of 500 MHz and is suitable for high-speed networks. This link class is used in 10GBase-T, among others.

Classes F and FA: Voice, data transmission and multimedia applications with frequencies up to 600 MHz and 1,000 MHz respectively. These link classes, specified according to E-DIN 44312-5, are suitable for use with ATM 155/622, Gigabit Ethernet and 10GBase-T of 10 Gigabit Ethernet.

ACR values in dB for link classes according to EN 50173 and DIN 44312-5

ACR values in dB for link classes according to EN 50173 and DIN 44312-5

Class "F" requires the use of four-pair single or overall shielded S/STP cables with high bandwidth, excellent near-end c rosstalk (NEXT), good attenuation characteristics and impedance characteristics. The RJ-45 connector is of limited use because the limits for near-end crosstalk and attenuation-to-crosstalk ratio (ACR) are only met when the outermost pins are occupied. For classes "E" and "F", the GG45 connector and the ARJ-45 connector have been standardized and the Tera connector has been developed.

Attenuation values in dB for link classes according to EN 50173 and DIN 44312-5

Attenuation values in dB for link classes according to EN 50173 and DIN 44312-5

Class FA: This link class is specified for frequencies up to 1 GHz. It requires data cables and data connectors of category 7A. Class FA cabling is characterized by significantly improved parameters compared to class "F". For example, the attenuation-to-crosstalk ratio (ACR) at 500 MHz is 28.3 dB better than that of the F class. Likewise, the values for external crosstalk (AXT) and powersum NEXT (PSNEXT) are significantly higher.

Class G is specified for frequencies up to 1 GHz. It is used in 10GBase-T, 40GBase-T and 100GBase-T.

The definitions, the designations and the scope of the link classes are different in the American EIA/TIA standard 568 compared to the international standard ISO/IEC 11801and the German standard DIN 50173.

EIA/TIA uses the term Category for the link class and knows the categories 3, 4 and 5.

While Class C and Class D links are similar to EIA/TIA Category 3 and 5 links, there are some key differences: 11801 explicitly excludes wiring at the workstation and terminal equipment wiring, such as the connecting cable that connects the personal computer (PC) to the junction box and the patch cord in the distribution area. The EIA/TIA connection takes these cables into account in the specification. This is critical in that the connecting cable is not a permanent part of the cabling system and can be replaced with a lower quality cable at any time, which would have a direct impact on the link class.

NEXT values in dB for link classes according to EN 50173 and DIN 44312-5

NEXT values in dB for link classes according to EN 50173 and DIN 44312-5

With the introduction of the new link classes "E" and "F", which are based on the new categories 6 and 7, the link definition has also been revised. Instead of the cabling section of the link, which comprises two connections and five metres of patch cord in the floor distributor, there is now only the permanent transmission section, i.e. from the patch panel to the telecommunications connection box, for the previous link classes "D", "E" and "F". In addition, the complete channel between two terminals is specified, taking into account all flexible connection lines. The channel specification corresponds to the link class already defined in EIA/TIA standard 568A.

Link model with channel definition

Link model with channel definition

The transmission links comprise two definition areas: The previous, Cabling Permanent Link, and the Transmission Channel Specification (Channel Performance).

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Englisch: link class
Updated at: 21.10.2018
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