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DAC or AOC, which is better?

In data centers, high-performance computers, mass storage and other devices, high-speed, high-reliability interconnect transmission is required. DACs and AOCs are commonly used to meet the demand, both of their ends have cable assemblies with factory-terminated transceivers, which are connected to fixed ports only. they look similar, do you know the difference and which is better for your applications?

What is DAC?

DAC

DAC means Direct Attach Cable, also known as direct connection cable or direct connection copper cable. The DAC transmits electrical signals over the copper cable, and does not involve electricity-to-light or light-to-electricity conversion. There are two types of DAC: passive DAC (Passive Copper Cable) and active DAC (Active Copper Cable).

The passive DAC is a shielded, high-speed copper cable with a SFP interface at each end. Since there is no any chip on the SFP interface, the signal will not be processed/converted when transmitting through the passive DAC.  It features low cost, ultra-low power consumption (less than 0.1 watts), and high reliability, but it is only working for short distance, usually less than 10 meters.

Active DACs are similar to passive DACs the big difference is that they have high-speed electrical signal compensation chips such as pre-emphasis and equalization to compensate for attenuation during electrical signal transmission and increase the data transmission distance between devices such as switches without compensation functions. Compared with passive DACs, its biggest feature is that its high-speed cable is thinner and the transmission distance is longer.

What is AOC?

40GBase QSFP+ AOC

Active Optical Cable, abbreviated as AOC, translates to active optical cable. The AOC is an optical fiber assembled with SFP Momodu at either end. There are optical transmitters and optical receivers on the circuit boards in the SFP modules, whose function is to convert the electrical signal into optical signal at the transmitting end, then send out it though the optical fiber, and convert the optical signal into electrical signal at the receiving end. Comparing to copper, optical fiber has a longer transmission distance(can reach 300m). But its cost and power consumption are higher than DAC since the photoelectric conversion, the design and processing process are more complex.

Passive DAC Active DAC AOC
Medium Copper Copper Optical Fiber
Signal Electrical Electrical Light
Cable diameter Big Medium Small
Transmission distance Short(<=7m) Medium(<=15m) Long(<=300m)
Power consumption Very low(Almost Zero) Medium(440mW) High(1~2W)
Cost Low Medium High
MTBF 500Mh 100Mh 1Mh

According to the features introduced above, here are the suggestion for you to choose the right products:

Conditions Suggestion
Limit budget & short distance DAC
Enough budget & short distance AOC
Medium distance(7~15m) AOC
Long distance (>15m) AOC

Generally speaking, AOC is suggested if budget is enough. AOC has some benefits: light weight, easy deployment, low bending radius and lowerBER. Only short distance and limit budget, the DAC is the preformed choice.

 

Before you make decision, make these questions clear:

What is the Application? Top of Rack, Middle of Row or End of row?

Is power consumption a consideration?

How much space is available in rack and cable pathways for cabling?

How long are the connections between ports?

What is your budget materials?

 

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