Whether to Choose 40G DAC or AOC Cables

With the top trend for data center and enterprises to move to higher data rate like 40G, relevant products and technologies are developed to back this new speed (e.g. the 40G optical transceivers and cables). However, there are so many options out there on the market. Network users usually don’t know how to make a choice. Take the 40G cables as an example, the most commonly used 40G cables are the 40G direct attached cable (DAC) and active optical cable (AOC). Each has its unique specification and usage. Which would be the most suitable one for connecting signals across the rack in data center? This article will provide you an ideal answer from the aspect of cabling performance, transmission distance and cost.

Brief Overview of DAC and AOC Cables

QSFP DAC cable is a form of high-speed cable with “transceivers” on either end used to connect 40Gbqs switches to routers or servers. QSFP+ DAC cable usually comes in either active or passive versions. They are widely available for short-reach 40G interconnect (within 7 meter). 40G DAC cables transmit 40GbE over short distances of parallel coaxial copper cabling. It uses a special cabling assembly with four lanes of coaxial cabling. Each transmit 10 Gbps for a total data rate of 40 Gbps. QSFP to QSFP and QSFP to SFP+ cable are the two common types of 40G DAC cables. The picture below shows a QSFP to SFP+ DAC breakout cable connected in a switch.

qsfp-to-sfp-dac-cable

AOC cable uses electrical-to-optical conversion on the cable ends to improve speed and distance performance of the cable while mating with electrical interface standard. Compared with DAC cables, its smaller size, longer transmission distance, lower insertion loss and electromagnetic interference immunity make it popular among subscribers. 40G AOC cables (see in the image below) can support longer distance than QSFP+ DAC cables (within 15m).

qsfp-to-sfp-aoc-cable

Comparison Between DAC and AOC Cables

After the brief introduction to the DAC and AOC cables, what to be considered next is the detailed comparison from the expects of cost, distance and cabling performance. The following chart shows a vivid comparison between them.

comparison-between-dac-and-aoc-cables

Cost

Cost is typically the No.1 factor affecting your selection. When it comes to 40G DAC cables, it is the same, although it’s quite clear that copper is much cheaper than optical cable. AOC, with connectors embedded with electronics and/or optics is the most expensive one. But it supports the highest transmission distance, many data centers won’t choose it because of the high cost.

While passive copper cable is much cheaper than AOC. However, the truth is that it cannot support 40G transmission in most cases in data center. Active copper cable is less expensive than AOC and can support longer transmission than passive copper cable seems to be a good choice. In this battle over cost, passive copper cable wins. But it is not suggested for 40G transmission in most cases.

Power Consumption

The main reason why DAC active copper cable and AOC can support longer transmission distance than passive cooper cable is that they are supported with active electronics. Passive copper cable requires no power. For 40G transmission, the power required for active copper cable is about 440mW, which is much less than that of AOC—2W. Thus, passive copper cable wins for its low power consumption.

Cooling System

Cooling is always crucial for data center, as it is closely related to the data center reliability and life of use. During DAC cable selection, two main factors can affect the cooling of data center. One is cable size. the other is the power consumption of direct attached cable. For the former factor, the thinner the cable is, the better dispersion devices in data center would have. AOC cable is the thinner than DAC cables. And DAC active copper cable is also thinner than passive cooper cable. The relation between power consumption and data center cooling is easy to understand. Higher power consumption can generate more heat in data center, which will load more burden on the data center cooling system. As mentioned before. AOC cable needs the highest power and DAC passive copper cable needs the lowest.

Transmission Distance

In the past, when the data rate required is less than 5 Gbps, the passive copper cables are used for interconnection. This type of DAC connects two SFP connectors by a copper cable, providing direct connection between cable ends via copper wire. Thus they are not expensive and robust with reliability. As it is passive, they need no power generally. However, when it comes to 40Gbps, they cannot satisfy such data rate in most cases. The passive copper cable with QSFP connectors attached on both ends can only support transmission 40 Gbps over very short distance. Thus passive copper cable is not suggested for regular 40G interconnection, unless 40G transmission is in very short distance.

Then AOC cable is introduced to overcome this challenge. Optical cables are thinner, flexible and can reach much longer distance up to 100 meters or more, which is much longer than that of the passive copper cable. However, AOCs are usually very expensive with the connectors attached on the active optical cable are embedded with optics and/or electronics. The connectors of the DAC active copper cable are embedded with electronics. Although they cannot support transmission distance as long as AOC, active copper cable can support longer transmission distance than that of the passive copper cable via copper wire. 40G transmission distance of active copper cable is about 15 meters.

To sum up, if you have a special requirement of the transmission distance. Then active optical cable wins with a transmission distance up to 100 meters. The active copper cable got the second place. And passive copper cable is at the last place. It is only suggested for 40G transmission over really short distance.

Conclusion

After comparing the performance of the DAC and AOC cables, we understand that the DAC passive copper cable is only suitable for really short-reach applications. While AOC cable possesses the best transmission performance but with higher cost in both material and daily use, and it needs more power as well. As for the DAC active copper cable, it can can support 40G transmission up to 15 meters with low power consumption, and satisfy the regular interconnection requirement for distance and cooling in most data center. What’s more, it is less expensive. FS.COM offers a full range of 40G QSFP cables including 40G DAC cable and AOC cables. Besides, the QSFP transceivers are also provided.

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Intel 40G QSFP+ Optics for Network Connectivity

With every step forward in Ethernet speed, low-cost network connectivity options have been sought for the broad adoption of the latest Ethernet infrastructure. Fiber optics, compared with copper solutions, have become the preferred connection choice available in telecommunication market for Ethernet deployment, no exception to 40 Gigabit Ethernet (GbE). This article mainly introduces Intel 40G QSFP+ optics used for network connectivity.

Intel 40G QSFP+ Optics Overview

Intel 40G QSFP+ optics, like Intel QSFP+ transceivers and Intel QSFP+ cables, are accessible for users who would like to deploy Intel Ethernet Converged Network Adapters. They deliver reliable solutions for deployments of high-density Ethernet for 40GbE network connections. Users can move efficiently to 40GbE for high bandwidth application requirements with Intel QSFP+ transceivers and cables. The flexible combination of Intel QSFP+ transceivers and cables enables users to create the configuration that satisfy best the needs of data center environment, while still ensuring compatibility among adapter and accessories.

Intel QSFP+ Transceivers

Intel QSFP+ supports high bandwidth application, such as content distribution, high-end virtualization using multiple CPUs, network appliances, and Applications Delivery Controllers (ACD) used for content caching, load balancing, and compression. Intel QSFP+ runs over multimode MPO trunks for short-range , and single-mode fiber (SMF) for long reach. These links are LC connectors terminated and can run up to 10km. This hot-swappable 40G I/O transceiver, Intel QSFP+, can also be used for QSFP+ to 4 SFP+ partitioned applications. One end of the connection is terminated with a MPO/MPT configuration, with four individual pairs terminated with LC at the other end. Intel QSFP+ enjoys the following features:

  • Support for 40GBASE Ethernet
  • Four channel, full duplex transceiver module
  • Maximum power dissipation < 1.5 W
  • RoHS-6 compliant (lead-free)
  • Commercial temperature range 0-70°C
  • Compatible with Intel Ethernet Converged Network Adapters
Intel QSFP+, high-bandwidth provider
Intel QSFP+ Cables

Intel QSFP+ cables provide a high density, high bandwidth solution at low cost and reduced power budget, available mainly in QSFP+ twinaxial cables and QSFP+ breakout cables.

Intel QSFP+ twinaxial cables are 40GBASE-CR4 802.3ba qualified passive copper cables that provide next generation performance by combining four 10G SFP+ channels into one affordable high-density QSFP+ package.

Intel QSFP+ breakout cables offer IT professionals a cost-effective interconnect solution for merging 40GbE QSFP+ and 10GbE SFP+ adapters, switches, and servers. Each cable features a single QSFP+ connector (SFF-8436) rated for 40Gbps on one end and 4 SFP+ connector (SFF-8431) each rated for 10Gbps on the other. This cable type allows users to bridge the gap between 10GbE and 40GbE cables, switches and adapters, and economically links a QSFP+ port with an upstream 10GbE SFP+ switch.

Conclusion

Intel 40G QSFP+ optics serve as a feasible choice for 40GbE connectivity, meeting the users’ bandwidth requirement well. AS a professional fiber optics products manufacturer and supplier, Fiberstore offers various Intel QSFP and cables which are 100% compatible with the original Intel 40G QSFP+ optics. Additionally, Fiberstore also provides 40G QSFP compatible with other major brands, like Cisco, Juniper and Brocade. You can visit Fiberstore for more information about compatible Intel 40G QSFP+ optics and other 40G QSFP brands.

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