Things You Must Know About DAC Cable

Fiber optic patch cable, also known as fiber jumper, is a fiber optic cable terminated with fiber optic connectors on both ends. And it is widely used in the connections between network equipment. In recent years, a kind of fiber optic patch cable which can transmit data at a high data rate with low cost is popular with data center users. That’s DAC cable or Direct Attach Cable, and this passage will focus on DAC cable’s overview, type and feature.

Overview of DAC Cable

Direct attach cable is a form of high speed cable with two connectors on either end which are in the form of optical transceiver module, such as SFP+, QSFP+ and so on, but they not real optical transceiver modules. Direct attach cable can support Ethernet, Infiniband, Fibre Channel and other protocols. And it is mainly used for the connection between switches, servers, routers in the interconnection application of racks. As a cost-effective solution in short reach applications, DAC is usually used in equipment distribution area (shown as the figure below).

Application of DAC Cable in Equipment Distribution Areas

Types of DAC Cable

Seen from the material of the cable, DAC can be classified into direct attach copper cable and active optical cable (AOC). Direct attach copper cable can either be passive or active, while AOC cable is always active. The following part will separately give an overview of passive direct attach copper cable, active direct attach cable and active optical cable.

Passive Direct Attach Copper Cable

Shown as the figure below, the connectors of passive direct attach copper cable contain no active components. The passive direct attach copper cable provides a direct electrical connection between corresponding cable ends and it can reach the transmission distance of 7m at a data rate of 10 Gbps or 40 Gbps with low power consumption.

Passive Direct Attach Copper Cable

Active Direct Attach Copper Cable

Compared with passive direct attach copper cable, the connectors of active direct attach copper cable contain active components, such as cable drive, to transmit and receive electric signals. Therefore, the active direct attach copper cable consumes more power. While these active components help to improve signal quality and provide a longer cable distance. For example, the active direct attach copper cable can reach the transmission distance of 15m at a data rate of 10 Gbps or 40 Gbps.

Active Direct Attach Copper Cable

Active Optical Cable

The material of AOC’s cable is fiber optic cable and the connectors of active optical cable contain active components, such as rear stage magnifying glass, laser driver and so on. As a result, the transmission distance of active optical cable is much longer than passive direct attach copper cable and active direct attach copper cable’s. Usually, the active optical cable can transmit signals up to 100m.

Active Optical Cable

Feature

From the content above, we can easily find that with different components inside connectors, different types of direct attach cables have different features. This part will give a detailed introduction about direct attach copper cable and active optical cable’s features.

For direct attach copper cable:

It supports higher data rates than traditional copper interfaces from 4 Gbps to 10 Gbps per channel.

It is interchangeable and hot swappable with fiber optical modules.

It is a cost-effective solution over optical transceivers and cables or short reach applications.

It supports multiple protocols, such as Gigabit & 10G Ethernet, 8G FC, FCoE, InfiniBand SDR, DDR & QDR.

For active optical cable:

It is an alternative to optical transceivers which eliminates the separable interface between transceiver module and optical cable.

Needing no equipment upgrades, it has a throughput of up to 40 Gbps with QSFP+; it weighs less than a comparable direct attach copper cable.

It is immune to electromagnetic energy because the optical fiber is a kind of dielectric (not able to conduct electric current).

Conclusion

DAC cable is a cost-effective, proven solution for interconnecting networking applications. It uses the same port as an optical transceiver, but with significant cost savings and power savings advantages in short reach applications. What’s more, the product is continuing to evolve to meet industry needs of higher data rates and densities with low power consumption.

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