100G CWDM4 vs. 100G PSM4: What's the Difference?
Mar 12, 20251 min read
The rapid development of cloud computing, artificial intelligence, and 5G has driven the demand for high-speed, cost-effective optical modules in data centers. Among the various 100G solutions, 100G CWDM4 and 100G PSM4 have gained significant attention due to their unique features and applications. Although both adopt the QSFP28 form factor, they differ significantly in technology, cost, and application suitability. This article aims to provide an in-depth comparative analysis of their specifications, application scenarios, and selection criteria to help you make informed decisions for network deployment.
What are 100G CWDM4 and 100G PSM4?
100G CWDM4 Definition
100GBASE-CWDM4 is a 100G optical module that uses Coarse Wavelength Division Multiplexing (CWDM) technology. It transmits four 25Gbps channels over a single pair of single-mode fibers, utilizing four wavelengths (1270nm, 1290nm, 1310nm, and 1330nm), with a 20nm wavelength spacing. QSFP 100G CWDM4 modules are designed for medium-distance transmission and are widely used in data center interconnects (DCI) and metro networks due to their cost-effectiveness and low power consumption.
The QSFP 100G CWDM4 module converts four electrical input signals into four CWDM optical signals and multiplexes them into a single optical channel for 100Gbps transmission. At the receiving end, the 100Gbps optical signal is de-multiplexed into four CWDM optical signals and then converted into four electrical output signals.
100G PSM4 Definition
The QSFP 100G PSM4 is a high-speed, hot-pluggable, low-power optical transceiver with a built-in digital diagnostics function. This module complies with the 100G PSM4 MSA standard and adopts a different transmission method. The PSM4 optical module transmits data over single-mode fiber at a wavelength of 1310 nm, supporting a maximum link distance of 500 meters when using PSM4 100G cables with MTP/MPO connectors. The 100GBASE PSM4 module provides four independent transmit and receive channels, each operating at 25Gbps, achieving a total data rate of 100Gbps.
The QSFP28 100G PSM4 converts parallel electrical signals into parallel optical signals through a laser array and transmits them in parallel over MTP/MPO single-mode ribbon fiber. At the receiving end, the PIN array converts the parallel optical signals back into parallel electrical signals.
100G CWDM4 vs. 100G PSM4: A Detailed Specification Comparison
Transmission Distance
100G CWDM4
Transmission Distance: Supports up to 2 kilometers via SMF.
Advantages: The low attenuation characteristics of single-mode fiber make it ideal for long-distance transmission scenarios such as Data Center Interconnect (DCI) and metropolitan area networks.
100G PSM4
Transmission Distance: Supports up to 500 meters via SMF (requires MTP/MPO-12 8-core fiber connector).
Advantages: Optimized for short-distance, high-density scenarios, suitable for intra-data center interconnects.
Laser Technology
100G CWDM4
Laser Technology: Uses four CWDM non-cooled Distributed Feedback (DFB) lasers, each operating at different wavelengths (1270nm, 1290nm, 1310nm, and 1330nm), with a 20nm wavelength spacing.
Advantages: CWDM technology allows multiple channels over a single fiber pair, reducing fiber requirements for longer reach.
100G PSM4
Laser Technology: PSM4 employs four independent 1310nm DFB lasers, each generating a 25Gbps optical signal, transmitted in parallel over four single-mode fibers.
Advantage: The parallel transmission design simplifies module complexity, making it suitable for short-range, high-density scenarios.
Fiber Type and Interface
100G CWDM4
Fiber Type: Single-mode fiber (SMF).
Interface: Duplex LC connector (enables bidirectional transmission on a single fiber).
Advantage: Simplifies fiber management, making it suitable for medium-distance interconnects.
100G PSM4
Fiber Type: Single-mode fiber (SMF).
Interface: MTP/MPO-12 connector (utilizing 8 cores to support 4-channel parallel transmission).
Advantage: Provides high-density connectivity, ideal for short-distance, multi-channel requirements.
Performance Parameters Comparison
To better understand the practical impact of these technical differences, let's compare the detailed performance parameters of the 100G CWDM4 and 100G PSM4 modules. The table below outlines their similarities and differences.
Product Specification | 100GBASE-CWDM4 | 100GBASE-PSM4 | |
Similarities | Form Factor | QSFP28 | QSFP28 |
Media | SMF | SMF | |
Power Consumption | ≤3.5W | ≤3.5W | |
Modulation Format | 4x25GNRZ | 4x 25G NRZ | |
Commercial Temperature Range | 0 to 70°C (32 to 158°F) | 0 to 70°C (32 to 158°F) | |
DDM/DOM | Supported | Supported | |
Differences | Wavelength | 1271nm, 1291nm, 1311nm and 1331nm | 1310nm |
Connector | Duplex LC | MTP/MPO-12 | |
Inbuilt FEC | Yes | No | |
Max Cable Distance | 2km | 500m | |
TX Power | -6.5~2.5dBm | -9.4~2dBm | |
Transmitter Type | 4 x CWDM DML (DFB) | 4x DFB | |
Protocols | IEEE 802.3ba, IEEE 802.3bm, 100G CWDM4 MSA, QSFP28 MSA, SFF-8665, SFF-8636 | QSFP28 MSA Compliant | |
Packaging Technology | COB (Chip on Board) Packaging | BOX Packaging | |
100G CWDM4 vs. 100G PSM4: Comparing Application Scenarios
When selecting between 100G CWDM4 and 100G PSM4 optical modules, understanding their respective application scenarios is crucial. Below is a detailed comparison of their typical use cases:
Application Scenarios of 100G CWDM4 Optical Modules
Mid-to-Long Distance Data Center Interconnection：100GBASE-CWDM4 supports a transmission distance of up to 2 km and requires only two single-mode fibers, significantly reducing cabling complexity and cost compared to PSM4, which requires eight-fiber connections. This makes QSFP 100G CWDM4 a mainstream choice for interconnecting data center rooms (e.g., between buildings or within a campus), particularly for large-scale cloud data center deployments.
Metro Network Edge and Access Layer: With a 2 km transmission capability, 100GBASE-CWDM4 meets the edge access needs of metro networks, such as connecting base stations to core network nodes or enterprise dedicated line access. It offers a lower-cost alternative to LR4 modules, which support 10 km transmission, making it suitable for cost-sensitive metro network deployments.
High-Density Network Architecture: For switches or routers that require high port density, QSFP 100G CWDM4’s duplex LC interface takes up minimal space, facilitating high-density port layouts. This makes it well-suited for cloud computing data centers with a flattened network architecture.
Application Scenarios of 100G PSM4 Optical Modules
Short-Distance Data Center Internal Interconnection: 100GBASE-PSM4 typically supports transmission distances of up to 500 meters and utilizes parallel single-mode fiber with an 8-fiber MPO interface. This makes it suitable for short-range connections within a data center, such as interconnections between Top-of-Rack (TOR) switches and core switches in hyperscale data centers.
Parallel Signal Transmission Scenarios: QSFP 100G PSM4 transmits signals over four separate fibers in parallel using the same wavelength (1310 nm). With its simple architecture, it is well-suited for internal networks that require high signal stability and low latency, such as financial trading systems or high-performance computing clusters.
Environments with Existing MPO Fiber Infrastructure: For networks that have already deployed MPO fiber infrastructure (e.g., upgrading from 40G to 100G), QSFP 100G PSM4 can directly reuse the existing cabling, eliminating the need for new fiber installation. This makes it a cost-effective solution for gradual network upgrades.
In summary, QSFP 100G CWDM4 and 100G PSM4 optical modules each have their unique application scenarios. When selecting, decisions should be based on actual network requirements, transmission distances, fiber types, and budget considerations.
100G CWDM4 vs. 100G PSM4: Which is the Best Choice for Your Network?
When choosing between 100G CWDM4 and 100G PSM4 optical modules, it is crucial to consider factors such as transmission distance, network architecture, and cost-effectiveness. Below is an extended guide to help make an informed decision:
Transmission Distance
Short Distance (≤500m): 100GBASE-PSM4 supports transmission distances up to 500 meters over single-mode fiber, meeting the demands of short-distance, high-bandwidth applications.
Medium to Long Distance (>500m): 100GBASE-CWDM4 supports transmission distances up to 2 km, effectively utilizing fiber resources and reducing fiber costs.
Network Architecture
Data Center Internal: 100G PSM4 is suitable for short-distance, high-density connections within data centers, such as connections between servers and switches, or storage networks.
Data Center Interconnects (DCI) or Metropolitan Area Networks: QSFP 100G CWDM4 is suitable for interconnections between data centers or metropolitan area networks, or other scenarios requiring long-distance transmission. It effectively maximizes fiber utilization and reduces deployment costs.
Power Consumption
Low Power Consumption: QSFP 100G PSM4 modules generally consume less power, making them ideal for data centers concerned about energy efficiency.
High Bandwidth Requirements: For scenarios requiring high bandwidth combined with long-distance transmission, QSFP 100G CWDM4’s wavelength-division multiplexing (WDM) technology offers greater flexibility and scalability.
Cost-effectiveness
100GBASE-PSM4: A lower-cost module, but it requires 8-core fiber and MTP/MPO cables, which increases wiring costs. It is more cost-effective for short distances due to its lower module cost and simplified design.
100GBASE-CWDM4: A more expensive module, but it only requires 2-core fiber, reducing fiber and wiring costs. It is more cost-effective for medium-distance transmission (up to 2 km) and is generally preferred over PSM4 in most cases.
General Advice
For short-distance, high-density interconnections with low power consumption, choose 100G PSM4.
For medium to long-distance transmission, where cost-effectiveness and limited fiber resources are important, choose 100GBASE-CWDM4.
It is important to assess your specific network requirements, including transmission distance, bandwidth needs, and cost considerations, before making a decision.
Whether you choose 100GBASE-PSM4 or 100GBASE-CWDM4, FS will provide you with high-quality products and services. These optical modules are equipped with Semtech and Macom chips, respectively, and feature a low power consumption of up to 3.5W, meeting the needs for both high performance and energy efficiency. They comply with the IEEE 802.3bm standard, support hot-pluggable QSFP28 MSA, ensuring perfect compatibility with a variety of devices, and provide powerful Digital Optical Monitoring (DOM) functionality for precise diagnostics and real-time configuration, further enhancing network stability.
All of our 100G optical modules undergo over 200 real-machine tests, along with strict compatibility testing with global brands such as Cisco, Arista, and Juniper, ensuring perfect adaptation to various devices and network architectures. This meets the requirements of a wide range of applications, including data center interconnection, data center interconnects, and metropolitan area networks. Additionally, FS's optical modules not only comply with international standards such as IEEE 802.3, but also pass stringent safety and compliance certifications, ensuring round-the-clock reliability and further improving network performance and user experience.
By choosing FS, you will receive a cost-effective solution with outstanding compatibility, reliability, and support services, ensuring your network runs smoothly and efficiently.
Conclusion
In conclusion, 100G CWDM4 and 100G PSM4 each offer distinct advantages, suited to different network requirements. 100G PSM4 is ideal for short-distance, high-density applications, while 100G CWDM4 excels in medium to long-distance transmission. Users should make a comprehensive decision based on actual transmission distance, fiber requirements, and cost. FS not only provides high-performance modules but also offers continuous guidance and support to ensure your network's performance, scalability, and efficiency, supporting future growth.