R&M Data Center Handbook

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3.9.1 Coax and Twinax Cables
The importance of using asymmetric cable media like coaxial and Twinax cables is being increasingly restricted to
areas outside of the data center network infrastructure. This is because symmetric cables, or so-called twisted pair
cables, are prevailing the copper area of the structured communication cabling system.
In data centers, coax cables (also called coaxial cables) are therefore found predominantly in cabling for video
surveillance systems and analog KVM switches.
Copper cables are often used in mass storage systems, since the connection paths between individual Fibre
Channel devices in these systems are generally not very long. A total of three different copper cable types (Video
Coax, Miniature Coax and Shielded Twisted Pair) are defined for FC with FC-DB9 connectors. Paths of up to 25
meters between individual devices can be realized by using these cables. In terms of copper transmission media,
Fibre Channel differentiates between intra-cabinet and inter-cabinet cables. Intra-cabinet cables are suitable for
short housing connections of up to 13 meters. These cables are also known as passive copper cables. Intercabinet
cables are suitable for connections of up to 30 meters between two FC ports, with transmission rates of
1.0625 Gbit/s. These cables are also known as active copper cables. The glass fiber media supported by FC are
listed in the table on page 103, along with their corresponding length restrictions.
IEEE 802.3ak dates from 2004 and was the first Ethernet standard for 10 Gbit/s connections over copper cable.
IEEE 802.3ak defines connections in accordance with 10GBase-CX4. The standard allows for transmissions at a
max. rate of 10 Gbit/s by means of Twinax cabling, over a maximum length of 15 meters. However, this speed can
only be guaranteed under optimal conditions (connectors, cables, etc.) 10GBase-CX4 uses a XAUI 4-lane
interface for connection, a copper cabling system which is also used for CX4-compatible InfiniBand (see 3.8.5). A
maximum connection of 10 meters is supported in 40 and 100 gigabit Ethernet (40GBase-CR4 and 100GBase-
CR10) using Twinax cables in 4- or 10-pair respectively (double Twinaxial IB4X- or IB10X cables respectively).
The examples above are still the best-known areas of application in data centers of asymmetric cables. As already
mentioned, future-oriented copper cable systems for network infrastructures consist of symmetric cables, or twisted
copper cables.
3.9.2 Twisted Copper Cables (Twisted Pair)
In designing a data cabling system in data centers that is geared for future
use, there really is no alternative to using twisted pair, shielded cables
and connectors.
This is not a big problem for cabling systems in the German-speaking
world, since this is already a de facto standard for most installations. The
possibility also exists to choose your required bandwidth from the large
selection of shielded cables and connectors (note: Category 6 or 6A are
also available in an unshielded version).
Cabling components based on copper (cables and connecting elements) can therefore be differentiated as follows:
• Category 6 (specified up to a bandwidth of 250 MHz)
• Category 6A / 6 A (specified up to a bandwidth of 500 MHz)
• Category 7 (specified up to a bandwidth of 600 MHz)
• Category 7 A (specified up to a bandwidth of 1,000 MHz)
As already mentioned in section 3.1.2 on page 47, ISO/IEC 24764 references ISO 11801 in the area of performance;
the current version of that standard was developed as follows:
• With its IEEE 802.3an standard from 2006, the IEEE not only published the transmission protocol for
10 gigabit Ethernet (10GBase-T), but also defined the minimum standards for channels to be able to
transmit 10 gigabit up to 100 meters over twisted copper lines.
• EIA/TIA followed with its 568B.2-10 standard in 2008 which set higher minimum standards for channels,
and also specified requirements for components: Category 6A was born.
• In the same year, the ISO/IEC 11801 published Appendix 1, which formulated even stricter requirements
for channels: channel class E A was defined. The definition of components remained open.
• This gap was closed in 2010 with publication of ISO/IEC 11801, Appendix 2. This new standard defines
components, i.e. Category 6 A cables and plug connections – note the subscript A – in the process
setting standards which surpass those of EIA/TIA.
Page 110 of 156 © 08/2011 Reichle & De-Massari AG R&M Data Center Handbook V2.0