SFP+ Twinax Direct Attach Cables for 1G to 10G Migration

As we know, the 10G SFP+ interface offers the highest density, lowest cost and lowest power 10 Gigabit Ethernet solution, while the SFP+ transceiver is published and available for achieving the migration from 1G to 10G network. However, if the mass 10G migration is required, the total cost for SFP+ fiber optical solution is still high. In order to reduce the cost for 10G migration, experts come up with the SFP+ twinax direct attach cable solution for 10G short distance transmission as a ideal cost effective alternative to the fiber optical solution. In this paper, it will mainly talk about the SFP+ twinax direct attach cable, which may be useful for you to deploy a 10G short distance transmission in a cost effective manner.

SFP+ twinax direct attach cable, also referred to as SFP+ DAC or 10G twinax cable, is a copper interconnect using a twinax cable assembly that connects directly into an SFP+ housing, designed for 10G short distance transmission. Compared to the fiber optical solution that basically requires two SFP+ transceivers and a optical fiber patch cable (SMF or MMF), the SFP+ twinax direct attach cable replaces them with a 10G twinaxial copper cable assembly that is very easy to install. In simple words, you only need to incorporate the SFP+ twinax direct attach cable into the physical infrastructure directly, then the 10G short distance connection can be accomplished without any extra signal processing or conversion.

As for its advantage, the SFP+ twinax direct attach cable not only features low cost, low power and low latency, but also has the smallest 10G form factor that facilitates the cabling. At present, it can be simply classified into two types, passive SFP+ twinax direct attach cable and active SFP+ twinax direct attach cable, which are designed for different applications.

As for the passive SFP+ twinax direct attach cable, it costs much less and has fewer components, only including capacitors, resistors, EEPROM and cable. Although it has no active Tx/Rx components, it is more reliable than the active one for no LOS, no TX disable and no interrupts. Meanwhile, there are limited management interfaces, which requires the host to do the work of driving it properly. In general, the passive SFP+ twinax direct attach cable has a fixed length, typically from 1 m to 7 m.

The active SFP+ twinax direct attach cable can be longer than the passive one, up to 15 m, which has a higher cost for the added benefits of being "optical-module" like. The most significant benefit is that there is no need to worry the host Tx/Rx for driving copper cables. Meanwhile, it enables pre-emphasis transmission and enhanced signal integrity that equalizes the active and adaptive receiving. In comparison with the passive one, the active SFP+ twinax direct attach cable has LOS, TX disable and interrupts, and more management interface, which can function as an optical transceiver.

Undoubtedly, the SFP+ twinax direct attach cable is an ideal solution for making the migration from 1G to 10G with lower cost, lower power and lower latency. Since there are two kinds of SFP+ twinax direct attach cables available on the market, it can be concluded from this paper that the passive SFP+ twinax direct attach cable is more reliable for the 10G short distance transmission but needs the host to drive the copper cable, which can be got at a fixed length from 1 m to 7 m, and it can be also concluded that the active SFP+ twinax direct attach cable is more expensive but has no the requirement for the host, which can be ordered with longer length, up to 15 m.