Direct Attach Cables (DAC) are high performance integrated duplex data link for bi-directional communication. And a SFP+ Direct Attach cable, also known as Twinax cables, uses SFP+ MSA and copper “twinaxial” cable with SFP+ connectors on both sides, provides 10 Gigabit Ethernet connectivity between devices with SFP+ interfaces. SFP+ Direct Attach Copper Cable is expected to be the optimum solution for 10G Ethernet reaches up to 10 m.
The concept of standard, structured cabling provides a long-term underlying foundation of transmission infrastructure that follows a base set of engineering rules. 10GBase-T retains and abides by this by operating over the installed base of twisted-pair copper cable already in place for lower-speed applications. 10GBase-T uses the same cabling-link-negotiating concepts as do 1GBase-T, 100Base-T and 10Base-T, providing a clear path of bandwidth upgradeability as needed, by leveraging the existing pair infrastructure. Within a rack, following link segment specifications, the same 10GBase-T copper twisted-pair cabling will enable use with earlier Ethernet generations – 10MB, 100MB and 1GB operation. To extend this further, this same copper twisted-pair cabling is utilized outside the equipment distribution area (EDA) zone, connecting with horizontal distribution area in the data center.
As a technology, 10GBase-T enables network managers to preserve their knowledge base of Ethernet transport while seamlessly upgrading bandwidth capacity from 1G to 10G rates. Additionally, network managers preserve their underlying investment in the maintenance of standard, structured cabling systems. But SFP+ Direct Attach Cable is supported only on 10G ports. Do not insert a DAC into a 1G port.
The IEEE 802.3an-2006 10GBase-T Ethernet Standard specifies operation over standard, structured twisted-pair copper cable up to 100 meters. In contrast, 10G SFP+ Direct Attach is limited to 10 meters, with a reach of five to seven meters more commonly available. SFP+ Direct Attach cables longer than five meters are exponentially higher cost compared to shorter cables.
As a standard, structured cabling system, twisted pair cables are a known technology to data center cable technicians. Twisted pair cabling offers the ability to field-terminate, as needed, clean lengths in less than a minute. 10GBase-T implementations enable just such a clean, structured cable infrastructure.
SFP+ Direct Attach cables, in contrast, cannot be field-terminated. SFP+ uses a passive twin-ax cable assembly and connects directly into a SFP+ housing; they are specially terminated at the vendor site and must be purchased at pre-determined lengths. This adds overhead to cable management inventory, while preventing a clean, efficient cable infrastructure design.
At a physical layer (PHY) device level, 10GBase-T power consumption, whether at full 100-meter reach or 30-meter short reach mode, will be higher than SFP+ Direct Attach, including the electronic-dispersion-compensation chip. A 10GBase-T PHY, at the device level, can consume anything from two to four Watts per port compared to two Watts per port for SFP+ Direct Attach.
SFP+ direct attach cables are widely used in varies condition for short distance 10G transmission, and 10GBASE-T works with Cat 6 and Cat7 cable that are commonly used for 1Gb network connections, which all have their own special applications.
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