Decoding 100G QSFP28 Fiber Optic Transceiver
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Decoding 100G QSFP28 Fiber Optic Transceiver

Posted on by FS.COM

Today, the trend for 100G is bullish and inevitable. To achieve 100G network, you can use 100G transceivers such as CXP, CFP, CFP2, CPAK, CFP4 and QSFP28. Among those optical modules that are capable of connecting 100G traffic, QSFP28 transceiver module is the most preferred module with smallest size and lowest power consumption.

100G QSFP28 Interface: MTP/MPO and LC Interface

100G QSFP28 fiber optic transceivers come in types like 100GBASE-SR4, 100GBASE-PSM4, 100GBASE-CWDM4 and 100GBASE-LR4, which have different interfaces. For 100GBASE-SR4 QSFP28 and 100GBASE-PSM4 QSFP28 modules, they are designed with MTP/MPO interface. This kind of QSFP28 module offers 4 independent full-duplex transmit and receiver channels, and each is capable of running up to 28Gpbs data rate per channel. Equipped with 100G QSFP28 MPO interface, these transceivers should be connected with a 12-fiber MTP/MPO patch cable.


For 100GBASE-CWDM4 QSFP28 and 100GBASE-LR4 QSFP28, they are configured with duplex LC interface. 100GGBASE-CWDM4 QSFP28 integrates transmit and receive path in one module with 4 lanes of optical signals (25.78125Gbps per lane) being multiplexed into an LC connector on the transmit side. And 100GBASE-LR4 QSFP28 is a fully 4x25Gbps transceiver module, which also works by multiplexing and de-multiplexing optical signals. They are all duplex modules and have to operate over single-mode fiber cable with duplex LC connector.


Maximum Supported Distance for 100G QSFP28 Transceivers: up to 80km

100G QSFP28 Transceivers can be used for both short-distance and long-distance transmission. For long link length, 100G QSFP28 LR4 optical modules are often adopted. They are designed for use in 100 Gigabit Ethernet links on up to 10km of single mode fiber, and compliant with the QSFP28 MSA, IEEE 802.3ba 100GBASE-LR4 and IEEE 802.3bm CAUI-4. The table below displays the maximum link length supported by other 100G QSFP28 transceivers.

100G Transceiver Types Maximum Distance Interface Fiber type
100G QSFP28 SR4 100m MTP/MPO-12 MMF
100G QSFP28 PSM4 500m MTP/MPO-12 SMF
100G QSFP28 CWDM4 2km LC Duplex SMF
100G QSFP28 LR4 10km LC Duplex SMF

The transmission distance of above mentioned 100G optical transceiver modules are restricted by 10km. What about if customers need to build a ultra long-haul network over 10km? Can 100G QSFP28 handle such a long distance? Now with the advent of 100G QSFP28 ER4, this can be achieved! Not very long ago, QSFP28 ER4 was still a promise and didn’t exist. But now some vendors like FS.COM can already provide it. It can support a distance up to 40km. Besides, 100G QSFP28 ZR4 transceiver is also said to be available this year, which will be able to handle a link length up to 80km.

100G QSFP28 Transceivers Breakout Solution

For customers who have need for upgrading to 100G from 25G, 100G QSFP28 also provides a flexible way for your network expanding. 100GBASE-SR4 QSFP28 transceiver can be connected to 4 25GBASE-SR SFP28 transceivers in the same way as 40GBASE-SR QSFP+ transceiver to be connected to 4 10GBASE-SR SFP+ transceivers. To achieve this connection, we simply need a 12f mpo lc patch cord.

100G Breakout Cabling Solution sfp28

Except by employing this mpo-12 to lc 100G QSFP28 to 4 SFP28 direct attach copper cables can also be used for 100G breakout cabling application. This breakout cable connects data signals from each of the 4 copper pairs on the QSFP28 end to the single pair of each of the SFP28 ends, enabling higher port bandwidth, density and configurability at a low cost and reduced power requirement in the data centers.

100G QSFP28 to 4 SFP28 direct attach copper cable

QSFP+ vs QSFP28: Can 100G QSFP28 Be Used for 40G?

As their name suggests, QSFP+ and QSFP28 differs in “28”. QSFP28 is a hot-pluggable transceiver module designed for 100G data rate. QSFP28 integrates 4 transmit and 4 receiver channels. “28” means each lane carries up to 28G data rate. While QSFP+ supports the data rate of 40G, 4 channels for transmitting and 4 channels for receiving, each lane carrying 10G.

Generally speaking, 100G QSFP28 transceiver cannot be used on 40G QSFP port. But it’s another case to insert a QSFP28 module into a 40G QSFP+ port if switches support. At this situation, a QSFP28 can break out into 4x10G like a QSFP+ transceiver module, thus being using for 40G. Also, QSFP28 connector is the same as QSFP+ connector (both are MPO12 cable connector) and QSFP28 pinout is identical to the QSFP+ pinout. For most switches, 40G QSFP+ can be used on 100G QSFP28 port.

Can We Use Third-party 100G QSFP28?

It’s known to us that 100G QSFP28 optical transceivers from original manufactures like Cisco tend to be much more expensive than those from third-party suppliers. So to purchase QSFP28 from third-party source is a huge money saver. But here comes the questions: How much can we save from the third-party suppliers? Can we trust it? Do there exist any hidden problems for using third-party transceivers? How about the after-sale service of third party suppliers? To know the answers, please read OEM Optics vs Third-Party Transceivers: Which to Choose?

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