40G DAC or 40G AOC ? Which Is Your Option？

In recent decades, we are so astonished at the fast updating in telecommunication field that we worried whether we can keep pace with the speed of innovation such as the revolution of iphone series. In terms of Gigabit Ethernet, Direct Attach Cable (DAC) and optical transceivers are main media for switches connection in data transmission. With regard to 40G transmission devices, there are main three types: QSFP+ DAC cables, QSFP+ AOC cables and QSFP+ optical transceivers. QSFP+ DAC cable is used for short range transmission over copper cable while QSFP+ AOC cable used for longer transmission via fiber optic cable. Do they have more differences? And how should we select? In this passage, we will provide a satisfied solution to you.

Overview on 40G QSFP+ DAC
DAC assembly is a high performance integrated duplex data link for two-directional communication over optical or copper cable. There is a transceiver shaped device on DAC cable’s either end used to connect switches to routers or servers. DAC here only refers to copper cable without optical lasers. 40G QSFP+ DAC copper cables are suitable for very short distance and offer a very cost-effective way to establish a 40 Gigabit link between QSFP ports of switches within racks and cross adjacent racks. There are three types of 40G QSFP+ DAC—40G QSFP+ to QSFP+ DAC, 40G QSFP+ to 4×SFP+ DAC, and QSFP+ to 4XFP DAC. With low cost, low power consumption and high performance, 40G QSFP+ DAC copper cables have been widely applied for data centers, Storage Area Network (SAN) and high-performance computing connectivity.

The below figure shows a 40G DAC cable.


Information About 40G QSFP+ AOC
Active Optical Cable (AOC) is designed for a higher data bandwidth in data transmission with standard electrical interfaces. It consists of multimode or single-mode fiber cable terminated with a connector. With a semiconductor within AOC cable, storage, data, and high-performance computing connectivity are accelerated. Compared with copper DAC, AOC provides more advantages, such as enhanced signal integrity, longer cable lengths, active/adaptive receive equalization, management interface, lower power consumption. lower connection loss and etc. But the cost of AOC is higher. There are three types of 40G QSFP+ AOC—40G QSFP+ to QSFP+ AOC, 40G QSFP+ to 4×SFP+ AOC, and QSFP+ to 8X DAC. Nowadays, 40G AOC are used to connect consumer devices such as cameras, HD TVs and enterprise networks which back up the modern data communication systems.

40G DAC Vs. 40G AOC
  • Transmission speed—Because of different transmission media, the transmission speed of 40G AOC is higher than 40G DAC via fiber optics. Besides, the transmission distance of 40G AOC is longer than 40G DAC.
  • Weight—Due to its material, AOC weighs less than a comparable DAC cable.
  • Color—Normally, the 40G AOC is orange while the 40G DAC is black.
  • Electromagnetic Interference (EMI) immunity—Since the optical fiber is a kind of dielectric (not able to conduct electric current), AOC is immune to electromagnetic energy.
40G DAC or 40G AOC? Which Is Optimal?
The specific circumstances and feasible measures will be fully covered in the following text.

Transmission Distance Is Under 5 m
40G DAC is highly recommended. A 5m Cisco QSFP-H40G-CU5M Compatible 40G QSFP+ Passive DAC cable is $65 while a 5m Cisco QSFP-H40G-AOC5M Compatible 40G QSFP+ Active AOC cable is $140.

Transmission Distance Is Over 5 m But Under 100 m
40G AOC is preferred. Passive DAC cable cannot meet such long reach requirement because of its performance limitation. 40GBASE-SR4 QSFP+ Transceiver can satisfy this reach need but the cost of the MTP trunk cable is so higher that the total amount of a transceiver and a trunk cable is $585. 40G AOC cable can arrive this distance with low cost. An 100 m Cisco QSFP-H40G-AOC100M compatible 40G QSFP+ AOC cable is $250.

Transmission Distance Exceeds 100 m
The 40G QSFP+ module for short-reach applications is ideal. For distance limiting, DAC cables and AOC cable are not suggested for distance exceeds 100 m. The cost of Cisco 40GBASE-SR4 is $85.

Summary
This passage focuses on information about 40G DAC, 40G AOC, differences between 40G DAC and 40G AOC as well as the alternative solutions. According to different requirement of transmission distance, you can choose the most suitable one for yourself.

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