05 Mar Important steps to consider before ordering DAC/AOC cables

Imagine a scenario where you want to implement a network topology using DAC cables. Let’s try to connect for example Dell QLogic 57810S 10GB PCI card with HP FlexFabric 5930 Switch using a 10 metres long DAC cable.

 

After inserting the DAC cable in both equipment units, the network link doesn’t go up. Nor trying to enable/disable port on the server or switch, nor physically pulling out and putting in the cable doesn’t help to solve to issue.

 

The solution of this problem can be found on both equipment documentations. On the datasheets we can see that this exact Qlogic PCI card supports only Passive Twinax (Copper) Direct Attach Cables (DAC) up to 7 metres. HP Switch supports DAC cables as well, but only up to 5 metres. For longer connections, this exact switch needs to be connected using an Active Optical Direct Attach Cable (AOC). So in this scenario, the only way to connect these units would be using a DAC cable in a shorter distance or connecting them using SFP+ transceivers with a patch cable.

 

So what are some essential steps that you should think about before ordering a DAC or AOC cable? As we can learn from the situation scenario above, it’s necessary to see if both equipment units you will be using the cable in does support the type and length cable you want to use. The best way to do it is by studying the datasheet of the equipment you will be using. The second step could be revising the pros and cons of both cables. DAC cables offers the client high data rates as 4Gbps to 10Gbps per channel and in the same time are more cost effective than using an AOC cable. On the other hand, AOC cables offer high data rates up to 40 Gbps with QSFP+ in the same time being lightweight and immune to electromagnetic energy.



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