100G CWDM4 vs. PSM4, What's the Difference?

With the rapid development of data centers, the distance supported by 100G SR4 is too short, and the cost is too high. In this case, the market ushered in the 100G medium-distance solution. 100G PSM4 and 100G CWDM4 optical modules are the main representatives of medium-distance transmission, but they have different applications and advantages. In this article, we will introduce the difference between 100G CWDM4 and 100G PSM4  to help you choose the right 100G QSFP28 transceiver.

   

100G PSM4 and 100G CWDM4 Overview

     

What is 100GBASE-PSM4?

  

Before introducing the 100G PSM4 optical module, let's first understand the 100G PSM4 standard. The 100G PSM4 (Parallel Single-Mode 4) standard is a Multi-Source Agreement (MSA) developed to provide a low-cost solution for transmitting four 25Gbps wavelengths over single-mode fiber in addition to the IEEE 100G Ethernet specification.

     

The 100G QSFP28 PSM4 transceiver complies with the 100G PSM4 standard and adopts a single-mode optical fiber parallel transmission mode. It has four parallel transmission channels, and the transmission rate of each channel is 25Gbps. The PSM4 optical transceiver can achieve 500-meter signal transmission on single-mode fiber with  1310nm wavelength. 

    

QSFP28 100G PSM4 is commonly used in the following typical applications:

   

Data Center Interconnect: Typically used to connect servers, switches, and routers within a data center to support high-speed, high-bandwidth communications.

   

High-performance Computing: In HPC environments requiring massive data processing and analysis, the QSFP28 100G PSM4's fast data transfer improves overall system performance.

  

Storage Area Network (SAN): Used to connect storage devices such as storage arrays and disk drives, the high data rate and low latency of this optical module ensures efficient data storage and retrieval.

  

What is 100GBASE-CWDM4？

  

100G CWDM4 QSFP28 is a standard announced in 2014, which is a 100G transmission mode based on single-mode coarse wavelength division multiplexing (CWDM) technology, and QSFP CWDM4 modules complying with this standard use duplex LC connectors and utilize four central wavelengths of 1271nm, 1291nm, 1311nm, and 1331nm for optical signal transmission.

       

How does the QSFP28 CWDM4 transceiver work? At the transmitter side, the 100G QSFP28 CWDM4 optical transceiver first converts four electrical signals with a transmission rate of 25Gbps into four CWDM optical signals, then multiplexes them on a single optical fiber for 100Gbps transmission. At the receiving end, the 100G QSFP28 CWDM4 optical module first decomposes the optical input signals into four channels of CWDM optical signals and then converts them into four electrical output signals. 

Why Do We Need 100GBASE-PSM4 and 100GBASE-CWDM4 Transceiver Modules?

   

The variety of 100G modules has actually been exceptionally large, such as the 100G SR4, 100G DR, 100G LR4, 100G FR, 100G ER4, and 100G ZR4, all of which are defined by IEEE standards. However, the transmission distances of these optical modules are often either too short or too long to fully meet the requirements of data center applications. For example, the 100G DR, like the 100G PSM4, can support distances up to 500 meters, but it does not support 100G to 4x25G applications and consumes more power. 

    

Some people must be puzzled, 100G QSFP28 LR4 optical transceiver can transmit 10 kilometers, which has covered the transmission range of 100G QSFP28 CWDM4 optical module, so why not use 100G QSFP28 LR4 optical module directly instead of choosing 100G QSFP28 CWDM4 optical module? This is because the power consumption and laser cost of 100G QSFP28 LR4 optical module are higher than 100G QSFP28 CWDM4 optical module, so in the transmission range of 2 kilometers, compared with the 100G QSFP28 LR4 optical module, choose 100G QSFP28 CWDM4 optical module is more economical.

   

Overall, the demand for 100GBASE-CWDM4 and 100GBASE-PSM4 optical modules stems from the need for cost-effective and efficient medium-haul transmission solutions in modern data centers.

   

PSM4 vs. CWDM4 QSFP28 Modules: Similarities You Should Know

   

Protocol

Both 100GBASE-PSM4 and 100GBASE-CWDM4 modules are defined by MSA.

    

Media Type

Both 100GBASE-PSM4 and 100GBASE-CWDM4 transceivers use single-mode fiber for 100G data transmission.

  

Lane Count

100GBASE-PSM4 and 100GBASE-CWDM4 achieve up to 100 Gbps using 4 lanes.

   

100G PSM4 vs. 100G CWDM4 Optical Transceiver: What's the Difference?

      

The table below helps you better understand these two 100G QSFP28 transceivers by comparing their differences in key features such as fiber count, connector type, operating wavelength, technology, transmission distance, operating principle, and cost.

    

From the above, we can learn that the characteristics and applications of 100G CWDM4 and PSM4 are different, so the selection should be evaluated and decided according to the actual demand and the design of Internet distance. Among them, the QSFP28 PSM4 optical module is the ideal solution for transmission distances less than 500m. On one hand, it can be used for a 100G to 100G direct connection. On the other hand, the QSFP28 PSM4 optical module can also be used to achieve 25G to 100G migration over short distances. However, from the point of view of comparing with the PSM4 optical module, not only the lower price but also the longer transmission distance, the advantages of the CWDM4 optical module are also more apparent, and from the present point of view, 100G CWDM4 is also the first choice of most people.

    

Conclusion 

     

In conclusion, both 100G PSM4 and 100G CWDM4 optical modules provide effective solutions for medium-distance 100G Ethernet transmission in data centers. Both 100GBASE-CWDM4 and 100GBASE-PSM4 are also suitable for high-density cabling, which is favored by most data centers. However, they also differ in price and application. Therefore, you can make a suitable choice according to your actual network requirements.