Backbone cabling

The function of the backbone cabling is to provide connections between the main distribution area, the horizontal distribution area, and entrance facilities in the data center cabling system.

Backbone cabling consists of the backbone cables, main connects, horizontal cross-connects, mechanical terminations, and patch cord or jumpers used for backbone-to-backbone cross-connection.

The backbone cabling is expected to serve the needs of the data center occupants for one or several planning phases, each phase spanning a time scale that may be on the order of days or months. During each planning period, the backbone cabling design should accommodate growth and changes in service requirements without the installation of additional cabling. The length of the planning period is ultimately dependent on the design logistics including material procurement, transportation, installation and specification control.

The backbone cabling shall allow network reconfiguration and future growth without disturbance of the backbone cabling. The backbone cabling should support different connectivity requirements, including both the network and physical console connectivity such as local area networks, wide area networks, storage area networks, computer channels, and equipment console connections.

6.3.2 Topology

6.3.2.1 Star topology

The backbone cabling shall use the hierarchical star topology as illustrated by figure 8 wherein each horizontal connect in the horizontal distribution area is cabled directly to a main connect in the main distribution area. There shall be no more than one hierarchical level of connect in the backbone cabling. From the horizontal connect, no more than one cross-connect shall be passed through to reach another horizontal cross-cross-connect.

Horizontal Distribution

Area Entrance

Room

Backbone cables Backbone cables

Main Distribution

Area

Horizontal Distribution

Area TR

Figure 8: Typical backbone cabling using a star topology

The presence of the horizontal connect is not mandatory. When the horizontal cross-connects are not used, the cabling extending from the main cross-connect to the mechanical termination in the equipment distribution area is considered horizontal cabling. If the horizontal cabling passes through the HDA, sufficient cable slack shall exist in the horizontal distribution area to allow movement of the cables when migrating to a cross-connect.

Backbone cabling cross-connects may be located in telecommunications rooms, equipment rooms, main distribution areas, horizontal distribution areas or at entrance rooms. In the case of multiple entrance rooms, direct backbone cabling to the horizontal cross-connect shall be allowed when distance limitations are encountered.

6.3.2.2 Accommodation of non-star configurations

The topology in figure 8, through the use of appropriate interconnections, electronics, or adapters in data center distribution areas, can often accommodate systems that are designed for non-star configurations such as ring, bus, or tree.

- Cabling between HDAs should be permitted to provide redundancy and to avoid exceeding legacy application distance restrictions.

6.3.3 Redundant cabling topologies

Redundant topologies can include a parallel hierarchy with redundant distribution areas. These topologies are in addition to the star topology specified in subclauses 6.2.2 and 6.3.2. See clause 8 for additional information.

48 6.3.4 Recognized media

Due to the wide range of services and site sizes where backbone cabling will be used, more than one transmission medium is recognized. This Standard specifies transmission media, which shall be used individually or in combination in the backbone cabling.

Recognized cables, associated connecting hardware, jumpers, patch cords, equipment cords, and zone area cords shall meet all applicable requirements specified in ANSI/TIA/EIA-568-B.2 and ANSI/TIA/EIA-568-B.3.

The recognized media are:

- 100-ohm twisted-pair cable (ANSI/TIA/EIA-568-B.2), category 6 recommended (ANSI/TIA/EIA-568-B.2-1);

- multimode optical fiber cable, either 62.5/125 micron or 50/125 micron (ANSI/TIA/EIA-568-B.3), 50/125 micron 850 nm laser optimized multimode fiber is recommended (ANSI/TIA-568-B.3-1);

- single-mode optical fiber cable (ANSI/TIA/EIA-568-B.3).

The recognized coaxial media are 75-ohm (734 and 735 type) coaxial cable (Telcordia Technologies GR-139-CORE) and coaxial connector (ANSI T1.404). These cables and connectors are recommended to support specific applications per annex A.

Channels constructed from recognized cables, associated connecting hardware, jumpers, patch cords, equipment cords, and zone area cords shall meet the requirements specified in ANSI/TIA/EIA-568-B.1, ANSI/TIA/EIA-568-B.2, ANSI/TIA/EIA-568-B.3 and ANSI T1.404 (DS3).

NOTES

1) Crosstalk between individual, unshielded twisted-pairs may affect the transmission performance of multipair copper cables. Annex B of ANSI/TIA/EIA-568-B.1 provides some shared sheath guidelines for multipair cables.

2) Annex C of ANSI/TIA/EIA-568-B.1 provides a brief description of a number of other backbone cables that have been used in telecommunications. These cables, as well as others, may be effective for specific applications. Although these cables are not part of the requirements of this Standard, they may be used in addition to the minimum requirements of this Standard.

3) See subclause 6.3.5 for backbone cabling distance limitations.

6.3.5 Backbone cabling distances

The maximum supportable distances are application and media dependent. The maximum backbone distances in annex A of this document provide application specific guidelines. To minimize cabling distances, it is often advantageous to locate the main cross-connect near the center of a site. Cabling installations that exceed these distance limits may be divided into areas, each of which can be supported by backbone cabling within the scope of this Standard.

Interconnections between the individual areas, which are outside the scope of this Standard, may be accomplished by employing equipment and technologies normally used for wide area applications.

The length of category 3 multipair balanced 100 Ohm backbone cabling, that supports applications up to 16 MHz, should be limited to a total of 90 m (295 ft).

The length of category 5e and 6 balanced 100 Ohm backbone cabling should be limited to a total of 90 m (295 ft). The 90 m (295 ft) distance allows for an additional 5 m (16 ft) at each end for equipment cables (cords) connecting to the backbone.

Data centers typically utilize patch cords that are longer than 5 m (16 ft). In data centers that use longer patch cords, the maximum backbone cabling distances shall be reduced accordingly to ensure that the maximum channel lengths are not exceeded. See subclause 6.2.3.1 for maximum lengths for copper patch cord information.

NOTES

1) The 90 m (295 ft) distance limitation assumes uninterrupted cabling runs between connects that serve equipment (i.e., no intermediate cross-connect).

2) Users of this document are advised to consult the specific standards associated with the planned service, or equipment manufacturers and systems integrators to determine the suitability of the cabling described herein for specific applications.

3) For copper cabling, in order to reduce the effect of multiple connections in close proximity on NEXT loss and return loss, the horizontal distribution area termination should be located at least 15 m (50 ft) from the main distribution area termination.