100G QSFP28 ER4 VS CWDM4: What is The Difference

Date 04/25/2025

This article compares the differences between 100G ER4 and 100G CWDM4 to help you understand their different application scenarios and choose the right module when deploying the network.

100G modules are becoming key components in data center and telecommunication network applications as network demands grow and network infrastructure upgrades. This article will take you through the two types of modules, 100GBASE ER4 and 100GBASE CWDM4, to help you understand their differences in performance and application.

What is 100G QSFP28 ER4

100G QSFP28 ER4 is defined according to IEEE 802.3bm and ITU-T G.959.1 P1L1-2D2 standards. It is an optical module for high-speed fiber optic communication. It uses 4x 25Gbps channels for transmission, but unlike ordinary modules, it uses LAN-WDM wavelengths and inherits forward error correction technology (FEC) to achieve a maximum transmission distance of 40km. QSFP28 ER4 can also use a single optical fiber to carry 4-channel wavelength data, saving optical fiber and port resources, and providing higher data transmission for high-density application environments. QSFPTEK's 100GBASE ER4 uses LC duplex patch cord transmission, NRZ modulation, EML at the transmitter, SOA+PIN at the receiver, and a maximum power consumption of ≤5W. It is widely used in telecommunications connections, data center interconnects (DCI), metropolitan area networks, and high-performance computing networks.

What is 100G CWDM4

100G QSFP28 CWDM4 is a short-distance to medium-distance optical module standardized by the CWDM4 MSA organization. It is an optical module for 100Gbps high-speed optical communication. It uses 4 CWDM wavelengths, 1271nm, 1291nm, 1311nm and 1331nm, and transmits data through LC duplex single-mode patch cords. The transmission rate of each channel is 25Gbps, and the maximum transmission distance is 2km. The QSFP28 CWDM4 module complies with the CWDM4 MSA and 100G CWDM4 standards and has wide compatibility. Compared with the 100G SR4 module, it can achieve 100Gbps data transmission with only dual-core single-mode optical fiber, saving wiring costs and being more cost-effective. QSFPTEK's 100GBASE CWDM4 uses NRZ modulation, the transmitter is CWDM DML, the receiver is PIN, and the maximum power consumption is ≤3.5W. It is mainly used in data centers, campus networks, enterprise core layers, etc.

Difference Between 100GBASE ER4 and 100GBASE CWDM4

Transmission Range

The main difference between QSFP28 CWDM4 and QSFP28 ER4 is their transmission distance. CWDM4 has a transmission distance of 2km, which makes it very suitable for campus internal links or data center internal links without the need to deploy additional equipment for amplification. ER4 has a transmission distance of 40km, which enables it to meet the needs of metropolitan, telecommunications and long-distance DCI.

Optical Devices

CWDM4 uses CWDM DML on the transmitter and PIN photodetector on the receiver. Although it has a shorter transmission distance, it has a lower starting price and lower power consumption. ER4 uses EML on the transmitter and SOA+PIN on the receiver. This optical device is more expensive and has a higher cost, but it can transmit farther and the signal is more stable.

FEC

Due to the short transmission distance, CWDM4 can operate without the use of FEC. ER4, on the other hand, requires the use of FEC to compensate for the long-distance signal attenuation. Although CWDM4 does not require FEC, FEC on the host side may still be applicable.

Power consumption

CWDM4 has a power consumption of less than 3.5W, which is suitable for use in high-density environments with limited heat dissipation and strict power budgets. Lower power consumption also generates less heat. ER4 has a power consumption of less than 5W. Because it uses high-performance lasers and integrated FEC, high power consumption enables it to transmit over longer distances, so when deploying 100G ER4, heat dissipation issues need to be considered.

Application environment

Application scenario	Module recommendation
Data center internal link (rack to rack)	100G CWDM4
Campus-level interconnection	100G CWDM4
Metro backbone network or MAN connection	100G ER4
Long-distance DCI	100G ER4
High-density deployment, low power consumption	100G CWDM4
Span loss network requires FEC	100G ER4

100G CWDM4 can not only be used for switch connection between racks inside the data center, but also support the connection between the switch and the server network card. When deployed at high density, it has the advantages of low cost, low power consumption and low heat generation. Its 2km transmission distance can also cover most connection requirements.

100G ER4 supports more medium and long-distance transmission, acting as a bridge between two data centers or between metropolitan area networks, connecting networks in two different places, such as connecting network cards on servers in two different data centers, so that data from the two data centers can be shared. The optical devices equipped with their lock have higher power consumption and are more stable and reliable during signal transmission.

Conclusion

There are differences between QSFP28 ER4 and CWDM4 in transmission distance, power consumption, optical devices, FEC and application environment. If you only need to transmit data within the data center or within a transmission distance of less than 2km, 100G CWDM4 can help you reduce network deployment costs and overall power consumption of the data center. If you need to transmit within a range of 40km, 100G ER4 with high signal transmission stability is your best choice.