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In data centers and enterprises, 40G QSFP+ series optical transceiver modules are generally used to build 40G network connectivity solutions. The modules most commonly used in 40G solutions include 40GBASE-LR4 QSFP+, 40GBASE-SR4 QSFP+, and 40G LR4 PSM. In addition to optical modules, high-speed cables DAC-40G QSFP+ and active optical cables AOC-40G QSFP+ are also within a specific range of use It has attracted more and more users’ attention, and they can meet some special needs. This article will introduce these 40G network connection technologies in detail. When you need to choose 40G optical modules and high-speed cables, this article will give you some analysis and help.

The Difference Between QSFP and QSFP+

QSFP is the abbreviation of Quad (4-channel) small form-factor pluggable transceiver, which is widely used in 40G Ethernet data transmission, it is a compact, hot-swappable transceiver. The internal transmission channel structure of QSFP+ is composed of 4 independent channels with a rate of 10Gb/s. The QSFP+ optical module supports Infiniband, SFF-8436 compliant, Fibre Channel, Ethernet, and other proprietary interconnects. QSFP+ stands for Quad Small Form Factor Pluggable Plus. It has a certain improvement in performance compared to the previous generation of QSFP. It has higher Ethernet bandwidth, each channel bandwidth reaches 10Gbps, and the rate of four channels is aggregated to 40Gbps. , which is compliant with Infiniband, Fibre Channel, Ethernet SAS, and SONET/SDH.

What is a 40G QSFP+ Interface?

The QSFP+ optical port is designed for 40G Ethernet, and the protocol is IEEE802.3ba-2010 and the MSA standard protocol, which defines the interface of the QSFP optical module family as 12-fiber MPO or duplex LC. 12-fiber MPO connectors are commonly used in optical modules using multimode fiber (MMF), and duplex LC connectors are commonly used in modules using single-mode fiber (SMF). For example, 40GBASE-SR4 uses MPO/MTP connector, and 40GBASE-LR4 uses an LC connector.

Introduction of Different 40G QSFP+ Optic Transceivers


The 40GBASE-LR4 optical module uses LC connectors, and it can reach a maximum transmission distance of 10km over single-mode fiber. The QSFP 40G LR4 optical module features 4 separate internal channels to transmit optical signals, each of which can perform transmission and receiving functions independently. It is important to note that these optical signals must be processed using MUX and DEMUX (optical device responsible for wavelength division) at the transmitter and receiver terminals in order to be multiplexed and demultiplexed.

The 40GBASE-LR4 QSFP+ optical module is defined by the 802.3ba standard and has a maximum transmission rate of 40Gbps, with each of its four internal independent channels having a transmission rate of 10.3125Gbps. when the 40GBASE-LR4 optical module is in operation, each channel transmits data over a single-mode fiber using a different wavelength, thus achieving 40Gb/s Ethernet transmission. The QSFP+ 40G LR4 is typically used for data links between data centers and Internet exchange points.


For the 40G SR4 QSFP+ optical module, it adopts the D3.2 standard, which defines the 40GBASE-SR4 module to use MPO/MTP connectors for 40G data transmission. 40GBASE-SR4 also uses 4 independent channels to transmit data, so its maximum transmission rate is the same as 40GBASE-LR4. The maximum transmission distance is 100m via OM3 multimode fiber and 150m via OM4 MMF. The QSFP+ 40G SR4 is typically used for interconnecting two Ethernet switches in a data center.

40GBASE-SR4 generally uses MPO/MTP interface, the difference between this optical module and 40GBASE-LR4 is that it generally uses multimode fiber optic breakout cable for data transmission, and the maximum transmission distance is different when using different wires, the maximum transmission distance is 100m when using OM3 and 150m when using OM4. QSFP+ 40G SR4 works on the principle that at the transmitting end, the laser array converts electrical signals into optical signals for transmission through optical fiber, and at the receiving end, the photodetector array converts parallel optical signals into parallel electrical signals. The following image shows how the QSFP+ 40G SR4 works.


The 40G LR4 PSM4 optical module involves optical/electrical connections and data digital diagnostic interfaces based on the QSFP+ multi-source protocol. 40G QSFP LR4 PSM module features a high level of integration and it has a higher port density, a feature that allows for more cost savings in data center operations. This module uses Parallel Single-Mode technology, a 4-way parallel design MPO/MTP interface to achieve high stability and efficient transmission over 10km.

The QSFP+ 40G LR4 PSM and QSFP+ 40G SR4 optical module transceivers work on the same principle, using laser arrays and photodetectors to convert optical signals to each other. 40GBASE-LR4 PSM optical modules are typically connected to single-mode fiber connectors and use 8 single-mode fibers to transmit parallel optical signals.

In summary, these three models are used in different places, QSFP+ 40G SR4 is generally used in data centers for short distances using OM3/OM4 ribbon cable to connect different Ethernet switches. 40G LR4 QSFP+ and 40G LR4 PSM optical modules are network solutions for long-distance transmission, using 40G LR4 QSFP+ optical modules can be more cost-effective than 40G LR4 PSM. PSM, because the former uses two single-mode fibers while the latter uses eight single-mode fibers, taking up fewer fiber resources.


QSFP DAC is a high-speed cable with a transceiver combined at both ends. It is generally used in 40Gbps switches to connect to routers or servers. QSFP+ DACs are available in passive and active versions. Its maximum transmission distance is 7m, so it can only be used for short-distance 40Gbps data transmission. The two most common 40GDAC cables include QSFP to QSFP and QSFP to SFP+ cables.

QSFP AOC performs the electrical-to-optical conversion at the end of the cable, and it conforms to electrical interface standards. The difference between it and QSFP DAC is that it has a smaller size, longer transmission distance, lower insertion loss, and immunity to electromagnetic interference, so it is quite popular in data. QSFP AOC supports a maximum transmission distance of 15m.


Before choosing the right 40G network solution, one should understand the differences between them. in conclusion, 40GBASE-SR4 and 40GBASE-LR4 use different interfaces and they have different transmission distances. 40G QSFP+ DAC cables have the advantage of being lower cost, lower power consumption, and better thermal performance. 40G AOC The transmission distance of the fiber optic cable has a longer transmission distance. These network solutions provide high-performance and cost-effective interconnections between servers and switches in the data center.

In-Depth Guide to 40G QSFP+ Optical Modules, DAC, AOC

What is SFP: SFP Meaning, SFP Types, SFP Port

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