Tag Archives: active optical cable

The Basics of Dirrect Attach Cables

Dirrect attach cable (DAC), is a cost effective and proven solution for interconnecting networking applications. It can provide inexpensive and reliable connections using either copper cables or fiber cables. What is DAC? How copper DAC and fiber DAC differ from each other? Here is what you need to know about DACs.

DAC Definition

A direct attach cable is a fixed assembly that is purchased at a given length, with the connector modules permanently terminated to each end of the cable to connect switches to routers or servers. DACs are much cheaper than the regular optics, since the “transceivers” on both ends of DACs are not real optics and their components are without optical lasers. They are preferable choice for their low cost, low power consumption and high performances. DAC are made of the two kinds of cable materials: copper and optical fiber. They are respectively called direct attach copper cable and active optical cable.

DAC Assemblies—Copper

Direct attach copper cable is interchangeable and hot swappable with fiber optic modules. It is designed in either active or passive versions. It supports such multiple protocols as Gigabit & 10G Ethernet, 8G FC, FCoE and InfiniBand. Direct attach copper cable is a cost effective solution over optical transceivers and and cables for short reach applications. It can support higher data rates than traditional copper interfaces—from 4Gbps to 10Gbps per channel. The defect of direct attach copper cable is that it is heavy and bulky, making it difficult to be managed. Furthermore, due to the nature of electrical signals, direct attach copper cable is vulnerable to the effects of electromagnetic interference (EMI), such as undesirable responses, degradation, or complete system failure. Fiberstore offers various QSFP+ direct attach copper cables with different lengths for your 40G applications. For example, lengths of Juniper EX-QSFP-40GE-DAC-50CM, QFX-QSFP-DAC-1M and QFX-QSFP-DAC-3M compatible QSFP+ to QSFP+ passive copper cables are respectively 0.5m, 1m, and 3m.

0.5m Juniper EX-QSFP-40GE-DAC-50CM Compatible QSFP+ to QSFP+ Passive Copper Cable

DAC Assemblies—Fiber

Active optical cable (AOC) is an alternative to optical transceivers, eliminating the separable interface between transceiver module and optical cable. It meets Small Form-factor (SFF) standards. Compaired to direct attach copper cable, AOC weighs less and can support longer transmission distance. It is immune to electromagnetic energy since the optical fiber is dielectric (not able to conduct electric current). What’s more, it is an alternative to optical transceivers and it can eliminate the separable interface between transceiver module and optical cable. AOC has no EMI. However, it costs more than copper cable.

Active_Optical_Cables

Applications of DAC

Direct attach cables are widely applied in storage area network, data center, and high-performance computing connectivity. They suppoet high speed I/O applications in storage, networking and telecom markets. And they can also be sused in witches, servers, routers, network interface cards (NICs), and Host Bus Adapters (HBAs). There are many different kinds of DACs, they all have their specific applicayions. For example, 40G AOC is commonly used for short-range multi-lane data communication and interconnect applications.

Conclusion

Fiberstore offers a variety of high speed interconnect DAC assemblies including 10G SFP+ cables, 40G QSFP+ cables, and 120G CXP cables to satisfy the demands from 10G to 100G interconnection. Direct attach cables provided by Fiberstore can be customized to meet different requirements. And we also offer all kinds of high quality QSFP+ modules branded by many famous companies, like Brocade QSFP+, Dell QSFP+, Juniper QSFP+, Finisar QSFP+, Intel QSFP+, etc. You can buy from us with confidence.

OM4 vs OM3

40G bandwidths are now being widely adopted within LANs and Data Centres. And 100G will soon be required within your local networks. Here comes the question: what type of fibre network you should choose when planning your 40/100 GbE migration. You have to consider your cabling infrastructure and how it will meet your current and future data requirements. The cables of choice for data center connectivity and what is recommended by the TIA are OM3 and OM4 laser-optimized multimode fiber. In this post, a comparison between OM3 and OM4 fibers will be given.

OM3- or OM4-Preferred Fibers in the Data Center

The IEEE 802.3ba 40/100G Ethernet Standard was ratified in June 2010 and specified parallel optics transmission for multimode fiber. OM3 and OM4 are the only multimode fibers included in the standard. OM3 and OM4 laser-optimized 50/125µm multimode fibers are the choice fiber type for connectivity in the data center. The fibers provide a significant value proposition when compared to single-mode fiber, as multimode fiber utilizes low cost 850 nm transceivers for serial and parallel transmission. Below we look at the differences between OM3 and OM4 multi-mode fibers. The picture shows laser-optimized multimode fiber cables.

laser optimised multi-mode fiber cables

Construction of the Fiber Cable

OM3 is fully compatible with OM4. The connectors are the same, the termination of the connectors is the same, the fibre core size 50/125 is the same, and both fibers are laser optimised multi-mode fiber (LOMMF). The difference is just in the construction of the fibre cable. The difference in the construction means that OM4 cable has better attenuation and can operate at higher bandwidth than OM3.

Attenuation: Attenuation is the reduction in power of the light signal as it is transmitted. It is caused by losses in light through the passive components, such as cables, cable splices, and connectors. The difference in OM3 and OM4 performance is in the loss (dB) in the cable. OM4 causes lower losses.

Dispersion: Dispersion is the spreading of the signal in time due to the differing paths the light can take down the fiber. Modal dispersion, which means that the spreading of the signal in time resulting from the different propagation modes in the fiber. OM3 specifies an effective modal bandwidth (EMB) of 2000 MHz/km, and OM4 of 4700 MHz/km, showing that OM4 can operate at higher bandwidth.

Cost Difference

The cost for OM4 is greater due to the manufacture process and economies of scale that the production of OM3 benefits from due to the volumes currently produced. Costs vary depending on the construction type of the cable (loose tube, tight buffered, etc.). OM4 cable is about twice as expensive as OM3 cable. This means that for lots of products such as standard fibre patch panels, MTP cassette modules, fibre patch cords the cost difference is very small (as the volume of cable is small).

What OM4 Gives You That OM3 Doesn’t?

OM4 effectively provides an additional layer of performance that supports these applications at longer distances, as shown in the following picture. OM4 provides an opportunity to future-proof cabling infrastructure, for it can provide a minimum reach of 125m over multimode fiber within the 40 and 100 GbE standards. Additionally, OM4 provides additional reach at extended bandwidth at an overall cost still less than that of an OS2 singlemode system. In other words, OM4 provides a solution that allows more installations to avoid the significantly higher costs of singlemode systems.

transmission distances

Conclusion

It is important to note that OM4 glass is not necessarily designed to be a replacement for OM3. Despite the relatively long-standing availability of OM4, there are no plans to obsolete OM3 fiber optic cabling. Fiberstore offers you a wide range of cable choices for your 40G Ethernet applications, like OM3 and OM4 fiber optic patch cables. And we also offer other 40G components, such as QSFP+ transceiver, copper cable, active optical cable and QSFP+ cable. You can buy from us with confidence.