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QSFP+ Breakout Cable Connectivity Guide for beginer's
Knowledge Base + 2023.12.12

Many data centers are facing upgrading the 10G Ethernet network to 40G. 40G QSFP+ breakout cables and transceivers are ideal 40G high-speed interconnection products for 10G-40G migrating. This article will introduce three 40G QSFP+ breakout connectivity solutions including 40G QSFP+ breakout DAC cable, QSFP+ breakout AOC cable, and QSFP+ optical transceivers+MTP-4xLC breakout cable.

Guide 1: QSFP+ to 4x10G SFP+ Breakout DAC(Direct Attach Cable)

QSFP+ breakout DAC cable is composed of a breakout copper cable, one QSFP+ module, and four SFP+ modules. These modules are all preterminated on the cable ends. The modules are inseparable from the copper cable. Compare to the common QSFP+ and SFP+ optical modules, those DAC modules don’t have expensive optical components, such as optical lasers.  

The QSFP+ to SFP+ breakout DAC cable connects to a 40G QSFP of a switch on one end, meanwhile,  on the other end, connecting to 4 10G SFP+ ports of the switch. These 40G to 4x10g breakout DAC cables are very suitable for short-distance interconnection applications. The passive QSFP+ breakout DAC cables are available within 7 meters, and the active cable types are available within 10 meters. They are generally used to interconnect within data center racks and across adjacent racks.

Guide 2: QSFP+ to 4x10G SFP+ Breakout AOC(Active Optical Cable)

QSFP+ breakout AOC is similar to QSFP+ breakout DAC. Both of them are composed of a breakout cable, one inseparable QSFP+ module, and four inseparable SFP+ modules, but the QSFP+ breakout AOC cable uses optical fiber cable as transmission media instead of copper cable, and the AOC pre-terminated modules have optical components while the breakout DAC doesn’t have. Therefore, the QSFP+ breakout AOC cable is more expensive than the DAC cable. And also, because of the fiber material reason, QSFP+ breakout AOC is much lighter and thinner than QSFP+ breakout AOC, and also more friendly for cable management. Moreover, since QSFP+ breakout AOC is made of fiber, it has no Electro Magnetic Interference (EMI) issues.

QSFP+ to SFP+ breakout AOC cable also connects to a 40G QSFP of a switch on one end and connects to four 10G SFP+ ports of the switch on the other end. The maximum transmission distance can reach up to 100 meters, which is longer than the QSFP+ breakout DAC.

Guide 3: QSFP+ Optical Module + MTP to 4xLC Breakout Fiber Cable

40G QSFP+ Transceiver Explained

The 40G QSFP+ (Quad Small Form-factor Pluggable) optical transceiver is used for 40G Ethernet optical transmission. It has 4 individual transmit channels and 4 individual receiver channels, each of which supports a rate of 10Gbps, and enables a total of 40 Gigabit Ethernet links. Some 40G QSFP+ transceivers can be used in 4x10G breakout mode, while others can’t. Then which 40G QSFP+ transceivers support a 4x10G breakout mode, the next article will tell.

Which 40G QSFP+ Transceivers Can be Used in 4x10G Connectivity?

QSFP-40G-SR4 and QSFP-40G-CSR4 Transceivers

Both QSFP-40G-SR4 and QSFP-40G-CSR4 optical modules are features with MTP/MPO interfaces. They support high-bandwidth 40G optical links over 12-fiber MPO/MTP female connectors at 850nm wavelength. The difference is that QSFP+ SR4 supports a transmission distance of 100 meters( via OM3) and 150 meters (via OM4), whereas the QSFP+ CSR4 supports an extended transmission distance of 400 meters over OM4.

Both of them can work at a 4x10G breakout mode for interoperability with four 10GBASE-SR modules by using an MTP to 4 LC multimode breakout fiber optic cable. The breakout connection diagram is shown below.1_5ff9ee8f-628d-4213-ac48-d5b73edd80c8_480x480.jpg

40GBASE-PSM4 Transceiver 

The 40GBASE-PSM4 optical module enables 40G link lengths up to 10km over Single-mode Fiber (SMF) over 12-fiber parallel fiber with MPO/MTP multifiber connectors. 

40GBASE-PSM4 can also work at a 4x10G breakout mode for interoperability with four 10GBASE-LR modules by using an MTP to 4 LC single-mode breakout fiber optic cable. The 40GBASE-PSM4 breakout connection diagram is shown below.


Can QSFP-40G-LR4 and QSFP-40G-ER4 Work at 4x10 Breakout Mode? 

 The answer is no. Why? Take 40GBASE-LR4 as an example. It transmits a 40G link length of 10km over a duplex LC connector. It adopts CWDM (Coarse Wavelength Division Multiplexing) technology, in the transmit direction, transmitting 4x10G optical signals to the DML laser with four CWDM wavelengths of 1271nm, 1291nm, 1311nm, and 1331nm. And then the 4 CWDM optical signals are multiplexed to a single-mode fiber over an LC connector. In the receive direction, the 40G CWDM optical signals input and demultiplex into 4 individual 10G optical data streams with different wavelengths. It can' work at 4x10G breakout mode since it can't be split into 4 individual duplex SMF fibers to achieve 4x10G breakout mode with a duplex LC connector structure.