Judging from transmission distance, 40GBASE-SR4 optics has better performance. According to the reliability, installation, maintenance and cost, 40G AOC is a better choice, cheaper and reliable.

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Fiberstore (FS.COM) | Two 40GbE Short-reach Solutions: 40GBASE-SR4 Optics vs. 40G QSFP+ AOC
Due to the huge amount of storage needed for great bandwidth services, like high-quality video
streaming and rapid file download, the demands for even higher speeds are increasing rapidly in
telecommunication and datacoms networks. To accommodate such fast-growing bandwidth
demands, the IEEE ratified standards to support 40 Gigabit Ethernet (GbE) in 2010, known as
802.3ba.
The IEEE standard 802.3ba released several 40-Gbps based solutions, including 40GBASE-LR4 optic
transceivers over single-mode fiber (SMF), 40GBASE-SR4 optics solution for multi-mode fiber (MMF).
The former is suitable for significantly long distances, while the latter is appropriates for short
distances. Actually, there is another component available to replace 40GBASE-SR4 optics when the
required distances are short in network interconnections, that is 40GBASE QSFP+ AOC (active optic
cable). This text mainly differs these two short-reach solutions for 40GbE transmission:
40GBASE-SR4 optics and 40GBASE QSFP+ AOC.
40GBASE-SR4 Optics
40GBASE-SR4 optics uses a 12-fiber MPO connector interface where all the 12 fibers are aligned in a
single row. Four fibers on one side are used to transmit, while another four on the other side are
utilized to receive, leaving the middle four fibers unused. In total, eight of the twelve fiber are used.
40GBASE QSFP+ AOC
As a kind of DAC (direct attach cable), AOC can be applied in 10G, 40G and even 120G. When used
in 40G transmission, two versions of AOC cabling assembly are available. The first one is QSFP to
QSFP, with QSFP+ connector on one end and another QSFP+ connector on the other end. The
Two 40GbE Short-reach
Solutions:
40GBASE-SR4 Optics
vs. 40G QSFP+ AOC

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Fiberstore (FS.COM) | Two 40GbE Short-reach Solutions: 40GBASE-SR4 Optics vs. 40G QSFP+ AOC
second is QSFP to four SFP+, with one end connected with a QSFP+ connector and the other end
with several SFP+ connectors. Like QSFP-4X10G-AOC10M, this 40G cabling product is the second
cabling assembly. Although the “transceivers” on both ends of AOCs are not real optics and their
components are without optical lasers, they have a similar function of real optic transceiver, and
also can transmission signals through fiber optic cables.
40GBASE-SR4 Optics vs. 40GBASE QSFP+ AOC
Both 40GBASE-SR4 optics and 40GBASE QSFP+ AOC are good solutions for interconnection. But
everything has two sides just like a coin. Each solution has its pros and cons. Figure out the
differences and choose the better component for your applications.
 Transmission Distance
The first point is the transmission distance. As what has been mentioned above, 40GBASE-SR4
optics and 40GBASE QSFP+ AOC are designed to support short distance transmission. When the
required distance is less than 100m, these two solutions have similar performance. But when link
length is longer than 100m, then 40GBASE-SR4 optics is the better choice. 40GBASE-SR4 transceiver
(eg. MC2210411-SR4) is able to realize 150m reach over OM4 MMF. Currently, most 40G AOC
provided by the telecommunication equipment manufacturers are less than 100m.
 Reliability
Reliability comes as the second factor to be considered. For interconnection use, both of the two
components should be inserted into a switch or a server. And the repeating plug of them is
necessary for daily use and maintenance, which might affect the performances of the component.
As such, reliability is of great importance during these daily actions. 40G AOC connectors are factory
pre-terminated, while QSFP+ SR4 transceivers are connected by additional MPO connectors and
fiber optic cables. In contrast, AOC is less affected by the repeating plug during daily use. AOC has
better reliability than that of transceivers.

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Fiberstore (FS.COM) | Two 40GbE Short-reach Solutions: 40GBASE-SR4 Optics vs. 40G QSFP+ AOC
 Installation and Maintenance
It’s clear that 40G AOC is easier for installation, since 40G AOC connectors are factory
pre-terminated. For working use, customers just need to plug the two connectors in the switches. In
comparison, as for QSFP+ SR4 transceivers, additional patch cords with MPO connectors are needed
to establish the link. When talking about maintenance, in case there was a fault in the
interconnection, for AOC, you can just replace it with another AOC. However, for interconnection
using QSFP+ SR4 transceivers, you have to locate the fault firstly by testing the patch cords and
optics, and then find the fault, which means a time-consuming task.
 Cost
In most cases, cost means a lot for users. Here cost includes two aspects: material cost and the
possible maintenance cost in daily use. As for the material cost, the price for 40G AOC is generally
cheaper than 40GBASE-SR4 optics, as the “transceivers” on both ends of AOCs are not real optics. In
a word, 40G AOC has advantages over 40GBASE-SR4 optics in both material cost and maintenance
cost.
Conclusion
Judging from transmission distance, 40GBASE-SR4 optics has better performance. According to the
reliability, installation, maintenance and cost, 40G AOC is a better choice, cheaper and reliable. For
your applications, Fiberstore supplies a sea of 40GBASE-SR4 transceivers (eg. MC2210411-SR4) and
40G QSFP+ AOC (eg. QSFP-4X10G-AOC10M). You can buy them at Fiberstore with lower prices and
enjoy high performance. Please visit www.fs.com if you want such a product.

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Fiberstore (FS.COM) | Two 40GbE Short-reach Solutions: 40GBASE-SR4 Optics vs. 40G QSFP+ AOC
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Notice: This document is for informational purposes only and does not set forth any warranty, expressed or
implied, concerning any equipment, equipment features, or service offered or to be offered by Fiberstore.
Fiberstore reserves the right to make changes to this document at any time, without notice, and assumes no
responsibility for its use. This information document describes features that may not be currently available.
Contact a Fiberstore sales team for information on feature and product availability.
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