SFP+ direct attach is a copper interconnect using a passive twinax cable assembly that connects directly into an SFP+ housing. It is low power, low cost and low latency with the added advantage of having the small form factor of SFP+, and smaller, more flexible cabling.

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SFP+ Direct Attach, as implied in the name, uses SFP+ MSA and by using the inexpensive copper twinaxial cable with SFP+ connectors on both sides, provides 10 Gigabit Ethernet connectivity between devices with SFP+ interfaces. SFP+ Direct Attach has a 10 meter distance limitation, thus the target application is interconnection of top-of-rack switches with application servers and storage devices in a rack.

 

The SFP+ interface offers the highest density, lowest cost, and lowest power 10 Gigabit Ethernet solution commercially available today. Further SFP+ enables mass migration of the 1GbE network to 10 GbE by offering a very low cost 10G SFP+ DAC (direct attach cable) option for short reach interconnects along with multi-mode and single mode fiber options. The SFP+ interface accepts along with hot-pluggable, small-footprint, optical transceivers, a direct attach cable, which replaces two optical modules and a connectorized optical fiber with a twinaxial copper cable assembly.

 

The 10G SFP+ copper direct attach cable option is defined for 10GbE applications over passive copper with a reach of 8.5m. The 10G SFP+ copper cable link utilizes a receive equalizer in the host PHY/SerDes in order to compensate for the Inter Symbol Interference (ISI) introduced by the cable. Electrical and mechanical specifications for SFP+ optical modules, 10G SFP+ copper cable, and hosts are defined in the SFF-8431 specification developed by the SFF Committee, with broad industry participation.

 

• Traditional passive copper — does not consume power and is an ideal choice for up to 12 meters. However, bulkiness, weight and signal integrity problems start to crop up at distances greater than seven to 10 meters. Limited bend radius and air flow blockage also are restricting factors.

 

• "Active" copper — thinner and lighter than passive copper, "active" copper's circuits draw power only at each end. Can extend to 15 to 20 meters.

 

SFP+ direct-attach twinaxial is relatively cheap as well. The downside is the distance limitation, max according to spec is 30m. In reality, trying to use it at the long end of that spec seems also to be frowned upon.

10GBASE-T will work with Cat 6 and Cat 7 cables that are commonly used for 1Gb network connections and also support much longer distances than SFP+ Direct Attach Copper. 10GBASE-T is currently not supported for OneConnect adapters due to power requirements and high latency of 10GBASE-T PHY chips. 10GBASE-T PHY technology continues to evolve and could be suitable for adapter products by the end of 2010.SFP+ DAC has lower latency than 10Gbase-T.