As interface speeds increase, fiber optic cables are more commonly used. At speeds above 10Gb/s, copper cables and connections show too much signal attenuation, even over short distances, such as within a single cabinet.

Single-mode and multimode fiber

Optical fibers can be single-mode or multimode. Single-mode fiber typically has a core of about 9 microns in diameter, less dispersion distortion than multimode fiber, and can transmit data over a distance of 80-100 kilometers or more, depending on the transmission rate, transceivers, and switch buffer sizes.

Multimode fiber has a core diameter of 50 or 62.5 microns and supports distances of up to 600 meters. The distance also depends on the transmission speed and the transceivers used.

Per meter, single-mode and multimode cables cost about the same. However, some other components required for transmission over single-mode cables are more expensive than their multimode counterparts.

The lifetime of optical cables is 15-20 years, so when planning a network, you need to choose cables that would support outdated, current and future data rates. It should also be remembered that laying new cables can be time-consuming, especially when installing in existing networks.

There are the following designations for fiber optic cables:

Multimode: OM1, OM2, OM3, OM4.
Single-mode: OS1 - for internal gasket, OS2 - for external.

OM3 and OM4 are new multimode cables that support 10GbE applications. These are the only multimode cables included in the IEEE 802.3ba 40G/100G Ethernet standard, ratified in June 2010. Speeds of 40G and 100G are achieved by connecting several parallel channels together. The standard defines distances of 100 meters for OM3 and 150 meters for OM4 for 40GbE and 100GbE. These are only rough estimates – real devices that support 40GbE and 100GbE can operate over shorter distances. The OM4 cable can operate in 32GFC networks at distances up to 100 meters.

The OM2, OM3, and OM4 (50 microns) and OS1 (9 microns) cables have a very small bending radius at which signal loss begins. The term BOMMF (Bend-optimized multi-mode fiber) is used to refer to this feature of OM2, OM3 and OM4 cables.

Single-mode OS1 and OS2 cables are used for transmission over distances of up to 10,000 m with standard transceivers and can be used for transmission over even longer distances using special transceivers and switching infrastructure.

Cable quality requirements

The Telecommunications Cable Systems Working Committee (TR-42) of the U.S. Telecommunications Industry Association (TIA) in 2012 approved the publication of a new telecommunications infrastructure standard for data centers TIA-942-A. Changes have been made to comply with the specification with modern capacity and energy efficiency standards, as well as to harmonize with current international standards.

The most important changes concerning trunk and horizontal connections are:

• The minimum requirement for a copper cable is a      Category 6 cable. For Ethernet networks, a Category 6a cable is      recommended.

• The minimum requirement for fiber optic cable is      OM3, it is recommended to use OM4 cables.

• The standard connector for SFP modules is LC.

Standards using 10 GbE fiber optic cables

10 GBASE-SR is the most common standard that uses SFP+ with a 10Gb optical transceiver.

10 GBASE-LR - "long-range" cables, using cables with single-mode fiber.

Difference between cables for internal and external routing

Cables for external gasket have additional protection against moisture and ultraviolet radiation. There are also universal cables that combine moisture, UV and fire protection to lay cables inside and outside the building without additional cable breaks.

Fiber Optic Cable Specifications

Maximum distance for data transmission

The distances in these configurations are usually less than those shown in the table. Distance values are given for multimode cables with a wavelength of 850 nm. Cables with a wavelength of 1300 nm support long distances.

Active and passive patch cords

Passive patch cords are suitable for most interfaces. But with increasing data rate, passive patch cords don't provide transmissions over a sufficient distance and take up too much space. Therefore, for high-speed connections such as 6Gbps SAS, active patch cords with copper cables are beginning to be used. Active patch cords include components to amplify the signal and reduce noise. In this case, you can use smaller cables, but increase the transmission distance. Active copper patch cords are cheaper and consume less electricity than those with fiber optic cables.

Ethernet standards using copper cables

1000BASE-T is typically used in 1Gb Ethernet and 1Gb iSCSI networks. It is a twisted pair with an RJ-45 connector. For connections, Cat5e and Cat6 cables are used.

10GBASE-T supports 10Gb Ethernet and 10Gb iSCSI traffic. The same cable is used as in 1000BASE-T, cat6a category only. The maximum cable length is 100 meters. Category 6 cables can also operate on 10GBASE-T networks at a distance of up to 55 meters, but require prior testing.

10GBASE-CR is a patch cord of a Twinaxial cable or "Twinax" (also known as DAC – Direct Attach Copper), the most popular type of cable for 10GbE networks, crimped by SFP+ transceivers. It is possible to use cables with a length of 1m, 3m, 5m, 7m, 8.5m and more. The most common are 3m and 5m.

10GBASE-CX4 is a rarely used standard. This type of cable and connector were previously actively used in InfiniBand SDR / DDR technology.