With the dramatic growth in data center throughput, the usage and demand for higher-performance servers, storage and interconnects have also increased. As a result, the expansion of higher speed Ethernet solutions, especially 10 and 40 Gigabit Ethernet has been ongoing. For 10 Gigabit Ethernet solution, selecting the appropriate 10-gigabit physical media is a challenge, because 10GbE is offered in two broad categories: optical and copper. This article will introduce both optical and copper cabling options for 10 Gigabit Ethernet.
Two general types of fiber optic cables are available: single-mode fiber and multimode fiber.
Single-mode Fiber (SMF), typically with an optical core of approximately 9 μm (microns), has lower modal dispersion than multimode fiber. It is able to support distances of at least 10 kilometers, depending on transmission speed, transceivers and the buffer credits allocated in the switches.
Multimode Fiber (MMF), with an optical core of either 50 μm or 62.5 μm, can support distances up to 600 meters, depending on transmission speed and transceivers.
When planning data center cabling requirements, be sure to consider that a service life of 15-20 years can be expected for fiber optic cabling. Thus the cable chosen should support legacy, current and emerging data rates.
10GBASE-SR — a port type for multimode fiber, 10GBASE-SR cable is the most common type for fiber optic 10GbE cable. It is able to support an SFP+ connector with an optical transceiver rated for 10GbE transmission speed. 10GBASE-SR cable is known as “short reach” fiber optic cable.
10GBASE-LR — a port type for single-mode fiber, 10GBASE-LR cable is the “long reach” fiber optic cable. It is able to support a link length of 10 kilometers.
OM3 and OM4 are multimode cables that are “laser optimized” and support 10GbE applications. The transmission distance can be up to 300 m and 400 m respectively.
Common forms of 10GbE copper cables are as follows:
10GBASE-CR — the most common type of copper 10GbE cable, 10GBASE-CR cable uses an attached SFP+ connector and it is also known as a SFP+ Direct Attach Copper (DAC). This fits into the same form factor connector and housing as the fiber optic cables with SFP+ connectors. Many 10GbE switches accept cables with SFP+ connectors, which support both copper and fiber optic cables.
Passive and Active DAC — passive copper connections are common with many interfaces. As the transfer rates increase, passive copper does not provide the distance needed and takes up too much physical space. So the industry is moving towards an active copper type of interface for higher speed connections. Active copper connections include components that boost the signal, reduce the noise and work with smaller gauge cables, improving signal distance, cable flexibility and airflow.
10GBASE-T — 10GBASE-T cables are Cat6a (category 6 augmented). Supporting the higher frequencies required for 10GbE transmission, category 6a is required to reach the distance of 100 meters (330 feet). Cables must be certified to at least 500 MHz to ensure 10GBASE-T compliance. Cat 6 cables may work in 10GBASE-T deployments up to 55 meters (180 feet) depending on the quality of installation. Some 10GbE switches support 10GBASE-T (RJ45) connectors.
To summarize, currently the most common types of 10GbE cables use SFP+ connectors.
- For short distances, such as within a rack or to a nearby rack, use DAC with SFP+ connectors, also known as 10GBASE-CR.
- For mid-range distances, use laser optimized multimode fiber cables, either OM3 or OM4, with SFP+ connectors.
- For long-range distances, use single-mode fiber optic cables, also known as 10GBASE-LR.