In general, the direct attach cable assemblies can be simply divided into two types, fiber type that can be called active optical cable (AOC), and copper type which basically includes active and passive direct attach copper cable (DAC), designed to support high transfer rates between servers, switches and storage devices intra rack or inter rack in data center. These direct attach cable assemblies have the same ports as their corresponding fiber optical modules, for instance, the SFP+ passive copper cable is fitted with SFP+ port, and QSFP+ passive copper cable with QSFP+ port. They are the ideal alternative to the fiber optical modules in high transfer rate and short distance applications for much lower cost and power consumption. Thereby, the direct attach cable assemblies become more and more commonly used for short distance network deployment.
The active optical cable consists of active electrical and optical components, which can transmit signals at lengths up to 100 m through multimode fiber cable. The most special active optical cable is the cable designed with fan-out technology like QSFP to 4xSFP+ AOC and 40G QSFP+ to 8xLC AOC for better satisfying the requirement of network migration from 10G to 40G. As for the internal structure of the active optical cable, you can learn it from the following figure.
At present, there are two kinds of direct attach copper cable. One is the active direct attach copper cable like SFP+ active copper cable, and the other is passive direct attach copper cable like QSFP+ passive copper cable. Compared to the fiber one, these two kinds of direct attach copper cables can support the 10G and 40G signals with shorter distance. As for the active direct attach copper cable, it features active component that can achieve the interconnection up to 15 m at 10 Gbps or 40 Gbps, but it also requires more power to boost/receive signals. As for the passive direct attach copper cable, it has no any active circuitry components which can only reach 7 m at 10Gbps or 40 Gbps at most, with low power. The figure below shows the differences between active and passive direct attach copper.
There is no doubt that the direct attach cable assemblies are good choices for short distance direct connection, usually applied in the EDA (Equipment Distribution Area) where the cabinets and racks house end equipment (servers) and where the horizontal cabling from the HDA (Horizontal Distribution Area) is terminated at patch panels. In details, the direct attach cable assemblies are used for connecting the server with the switch, the storage with the switch, or the switch with the switch in racks and between rows of racks. Besides, various length selections for the direct attach cable assemblies such as SFP+ passive copper cable and QSFP+ active copper cable can be ordered to meet different connection requirement.
With the popularity of 10G Ethernet network, the 10G SFP+ DAC (within 15 m) and 10G SFP+ AOC (within 100 m) occupy the major direct attach cable assemblies market for interconnection in the same rack or between rows of racks at present. Meanwhile, the SFP28 DAC is also designed for 25G Ethernet network which may gradually replace the 10G SFP+ DAC for higher transfer rate. What’s more, for meeting the fast development of Ethernet network, 40G QSFP+ DAC for short interconnection no longer than 15 m and 40G QSFP+ AOC for longer interconnect application that over 15 m but less than 100 m are also available for 40G Ethernet network. If these direct attach cable assemblies still can’t satisfy your requirement, then the 100G QSFP28 DAC and AOC are highly recommended for you to deploy in the 100G Ethernet network.