How to use SFP cables?
How to use SFP cables?
SFP cable, also known as 10G SFP+ cable, SFP+ DAC twinax cable or SFP+ AOC cable, is a form of high speed cable with Small Form Factor Pluggable Plus on either end. They are suitable for in-rack connections between servers and switches. SFP cable’s popularity can be attributed to that Cat5e copper cabling and 1000BASE-T have dominated data center interconnection application for years, however, the upgrading to 10GE, 40GE and beyond poses a significant hindrance in both power consumption and cost. At this point, 10G SFP+ direct attach copper swoops in and becomes a new favor of Top of rack switching.
What Is SFP Cable?
SFP twinax cable which replaces two optical modules and a connectorized optical fiber with a twinaxial copper cable assembly offers the higher density, lower cost, and lower power 10 Gigabit Ethernet solution than other cable types such as 10GBASE-CX4 and CAT6/CAT6A 10GBASE-T. The SFP cables can be classified to 10G SFP+ DAC cable and 10G SFP+ AOC cable. SFP+ AOC features longer transmission distances(>100m), isolation from signal interference and crosstalk and higher signal transmission capacities but it’s more expensive than SFP+ DAC. SFP+ DAC consists of active DAC and passive DAC. Passive DAC cables have no signal amplification built into the cable assembly hence for ultra short reach(<5m), whereas active DAC cables have signal amplification and equalization built into the cable assembly for a litter longer reach(5-15m) in the same time with a higher price.
| Attribute | Passive DAC | Passive DAC | AOC |
| Cable Type | Twin-axial copper | Twin-axial copper | Fiber optic |
| Maximum Reach | <7 m | 7-15 m | 100 m+ |
| Power Consumption | <0.15 | 0.5-1w | 1-2 W |
SFP Cable: 10G SFP+ Cable vs. 25G SFP28 Cable
We’ve already known that SFP+ is made to operate at 10Gb/s. And SFP28, as the enhanced version of SFP+, is designed for 25G signal transmission. SFP28 utilizes the same familiar form factor as SFP+, but the electrical interface is upgraded to handle 25Gbps per lane. To put it simply, 10G SFP+ cable and 25G SFP28 cable just has the same form factor but with different speed. What’s more, 25G SFP ports can support a full range of 10G SFP+, which means 10G SFP+ cable can be plugged into 25G SFP ports.
How SFP Cable Is Used?
As 10G network is widely deployed in today’s data center, 10G SFP cables are commonly used in interconnect applications below 100m, such as server to switch or storage to switch interconnection in the same rack (Shown in the below picture). And now 25GbE is popular and 25G direct attach cable assemblies, such as SFP28 DACs, are already available in the market. For 40GbE, 40G QSFP+ DACs and AOCs are used. Of course, higher speed and more bandwidth are needed for spine switches. Thus, 100G DACs, like QSFP28 DACs are used in this case.
