100GBASE-SR4 vs 100GBASE-PSM4, What are the Differences?

What is 100GBASE-SR4?

QSFP28 100GBASE-SR4 is an optical module for short-distance high-speed transmission, often used to achieve 100G Ethernet connection through multimode fiber (OM3/OM4). It uses 4 parallel 25Gbps channels, connected through MTP/MPO-12 interface, and the maximum transmission distance can reach 70~100 meters under OM4 fiber. SR4 modules are widely used for internal connections in data centers, such as between Top-of-Rack (ToR) switches and aggregation switches. They have the advantages of high bandwidth, low power consumption and high cost performance, and are one of the mainstream solutions for building short-distance 100G networks.

What is 100GBASE-PSM4?

QSFP28 100GBASE-PSM4 module is used for medium and long-distance transmission, supporting 100G data transmission through single-mode fiber, with a maximum distance of up to 500 meters. This module is also based on 4 25Gbps channels, but unlike SR4, it uses MTP/MPO-12 interface to transmit 4 optical signals (4Tx/4Rx) in parallel in single-mode fiber. PSM4 is a lower-cost long-distance solution suitable for connectivity needs within data centers or across buildings in campus networks. It is particularly suitable for scenarios that are sensitive to power consumption but do not require a link budget of several kilometers.

100GBASE-SR4 vs 100GBASE-PSM4, What are the Differences?

Overview of Core Differences

Feature	100GBASE-SR4	100GBASE-PSM4
Transmission medium	OM3/OM4 MMF	OS2 SMF
Transmission Distance	OM3：70m OM4：100m	500m（Standard）
Wavelength	850nm（4-channel VCSEL Laser）	1310nm（4-channel DFB Laser）
Connector Type	MPO-12（8-core transmitter + 8-core receiver）	MPO-12（4-transmitter 4-receive bidirectional multiplexing）
Power Consumption	2.5-3.5W（low）	3.5-4.5W（higher）
Cost	US$ 39.9（low）from QSFPTEK	US$ 153.9（higher）from QSFPTEK

Technical Principles

SR4: Parallel multimode solution

• Through 4 independent 850nm VCSEL lasers, 4×25Gbps data is transmitted in parallel on 8-core multimode optical fiber (MPO-12 interface).
• Advantages: low power consumption, low heat generation, compatible with existing machine room OM4 wiring (no need to replace optical fiber).

PSM4: Single-mode wavelength division scheme

• Uses 4-channel 1310nm DFB lasers to transmit data through 4 independent channels of single-mode optical fiber, relying on precise wavelength control.
• Advantages: 500m long-distance support, strong anti-interference, suitable for cross-cabinet backbone connection.

Application Scenario Selection Guide

Scenario	Recommended solution	Reason
In-cabinet equipment interconnection	SR4	Short distance (<100m), OM4 fiber cost is only 1/3 of single-mode, and SR4 module power consumption is 30% lower
Cross-cabinet/floor backbone connection	PSM4	500m distance coverage, single-mode fiber has no modal dispersion problem, and signal stability is better
10G to 100G smooth upgrade	SR4	Existing 10G MMF wiring can be reused through MPO splitter (such as 24-core MPO is split into 3 groups of SR4)
High-density data center	PSM4	Single-mode fiber has a thinner fiber diameter (9μm), saving 90% of the cable trough space compared to multi-mode (50μm)

 

Performance Test Data Comparison

Parameter	SR4（OM4, 100m）	PSM4（OS2, 500m）
Bit error rate (BER)	＜1E-12	＜1E-12
Link delay	0.1μs	0.15μs
Optical power tolerance	±2.5dBm	±1.8dBm（stricter requirements）
High temperature stability（85℃）	Attenuation increase ≤0.2dB/km	Attenuation increase ≤0.3dB/km

Note: PSM4 requires strict calibration of optical power due to the low dispersion tolerance of single-mode fiber

Future Evolution Trend

SR4 alternative: The next generation 200G-SR4 (PAM4 modulation) is commercially available, reusing the same MPO fiber.

PSM4 upgrade path: smooth transition to 400G-DR4 (500m), wavelength remains at 1310nm.

Cost optimization: Silicon photonics integration technology reduces PSM4 power consumption to 2.8W, and the unit price is expected to drop below $100 (2025).

100GBASE-SR4 vs 100GBASE-PSM4, How to Choose?

Limitations of SR4:

Multimode fiber has modal dispersion, and the bit error rate soars over 100m, and OM5 fiber cannot break the 150m limit.

Compatibility issues: The old OM1/OM2 fiber does not support (the maximum distance is only 33m).

Challenges of PSM4:

High laser cost: The price of DFB laser is 3 times that of VCSEL, which pushes up the unit price of the module.

Strict cleaning requirements: The dust tolerance of the single-mode fiber MPO interface is less than 0.5μm, and special tools are required for maintenance.

Summary:

Choose SR4 if: limited budget, short distance in the equipment room (≤100m), existing multimode cabling.

Choose PSM4 if: need to cross cabinet backbone (≤500m), high-density deployment, and future compatibility with 400G.

Actual case: A cloud service provider uses SR4 to save costs at TOR (Top of Rack), and PSM4 to ensure stability at the spine layer, saving 35% of optical module expenses.