56G QSFP+ DAC Vs. 40G QSFP+ DAC

High speed data transmission is the prerequisite for enterprise network deployment. For big data centers, 40G is still the mainstream. For 40G network, 40 gbps transceiver and 40gb ethernet cable are important components, and they can be classified according to transmission distance. For long transmission distance, there are 40G LR4 QSFP+ transceiver and singlemode fiber cable; for short transmission distance, there are 40G SR4 QSFP+ transmission and multimode fiber cable. In addition, for 40G short link, there is QSFP+ DAC cable. Two types of QSFP+ DAC cables are available on the market: 56G QSFP+ DAC vs. 40G QSFP+ DAC, what’s the difference between them? This article will make a comparison.

56G QSFP+ DAC Vs. 40G QSFP+ DAC: Same construction

We know that DAC cable is a kind of high speed passive copper cable with one connector on each end. The connectors are not real optical transceiver modules but in the form of optical transceiver module. DAC twinax cable Therefore, QSFP+ DAC consists of two QSFP+ transceiver style connectors and one twinax copper cable. With the same construction, the operation of 56G QSFP+ DAC and 40G QSFP+ DAC in 40G network deployment is the same, too. Just plug the connector into 40G QSFP+ port on the switch on both sides, and then you can get 40G link. Here is a figure of QSFP+ DAC cable for you.

QSFP DAC

56G QSFP+ DAC Vs. 40G QSFP+ DAC: Different protocols

As qsfp+ passive copper cable, both 56G QSFP+ DAC and 40G QSFP+ DAC are QSFP MSA compliant. But 40G QSFP+ DAC supports 40G InfiniBand 8x DDR, 4x QDR, 10G/40Gigabit Ethernet, Fibre Channel, while 56G QSFP+ DAC supports 40G InfiniBand 4x FDR, 56Gigabit Ethernet, Fibre Channel. What’s the different between InfiniBand DDR, QDR and FDR? InfiniBand (abbreviated IB) is a computer-networking communications standard used in high-performance computing that features very high throughput and very low latency. It is used for data interconnect both among and within computers. InfiniBand is also used as either a direct or switched interconnect between servers and storage systems, as well as an interconnect between storage systems. And the following figure shows InfiniBand specification. We know that QSFP+ DAC cable uses four channels for data transmission. And for 40G QSFP+ DAC, it supports 40G InfiniBand 8x DDR, 4x QDR, so each channel can achieve 10G data rate; for 56G QSFP+ DAC, it supports 40G InfiniBand 4x FDR, so the maximum data rate of each channel is 14G.

InfiniBand Specification

Conclusion

Characterized by low Insertion loss and power consumption, qsfp+ passive copper cable is a cost-effective option for 40G data transmission over short distance. As for 56G QSFP+ DAC vs. 40G QSFP+ DAC, the only different is that the former can operate high bandwidth than the latter one. Therefore, if your network needs 40G data transmission, then 40G QSFP+ DAC cable; if you need more than 40G bandwidth, then choose 56G QSFP+ DAC.

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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.