You just ran a utilization report on your data center’s core switch, and the message is clear: the 40G links are hitting peak capacity. The explosion of AI, machine learning, and high-performance computing (HPC) demands more than your current network can offer.
The decision before you is crucial: Should you stick with the familiar 40G QSFP+ standard, or make the leap to the far more powerful 100G QSFP28?
While both modules share the same physical size, they represent two different generations of optical technology. This expert guide provides a definitive technical and financial comparison, offering the necessary authority and expertise to ensure you make the right, future-proof decision for your high-speed network.
Understanding the QSFP Evolution
The QSFP (Quad Small Form-factor Pluggable) family was introduced to solve a major problem: how to transmit 40G, 100G, and eventually 400G+ data rates using a compact, single module. The “Quad” in the name is the key—it means the module uses four parallel transmission lanes to achieve its speed.
What is QSFP+ (40 Gigabit)?
The QSFP+ module achieved 40 Gigabit Ethernet by dedicating each of its four lanes to 10 Gbps of data.
- Core Technology: Operates as 4 lanes of 10Gbps (4 x 10G).
- Signaling: Uses NRZ (Non-Return-to-Zero) modulation, the traditional method of representing a ‘1’ or ‘0’ by the presence or absence of a signal pulse.
- Key Applications: The 40G QSFP+ was the standard for the aggregation layer and ToR (Top-of-Rack) switches during the shift from 10G to 40G networking.
What is QSFP28 (100 Gigabit)?
The QSFP28 is the successor to the QSFP+. The number ’28’ refers to the fact that each of the four electrical lanes now handles a maximum of 28 Gbps of data.
- Core Technology: Achieves 100 Gigabit Ethernet by operating as 4 lanes of 25Gbps (4 x 25G).
- Signaling: Primarily uses NRZ (for common short-reach and long-reach applications). Crucially, the QSFP28’s electrical platform is the required foundation for PAM4 (Pulse Amplitude Modulation 4-level), the signaling method for next-generation 200G/400G deployments.
- Key Applications: This is the current foundation for modern Spine and Leaf architecture, as well as high-capacity Data Center Interconnect (DCI).
QSFP+ vs. QSFP28: The Definitive Technical Breakdown
When evaluating 40G vs. 100G, the comparison must move beyond the simple price tag and focus on efficiency, flexibility, and TCO.
1. Data Rate and Signaling Efficiency (The Physics)
While both modules use four optical lanes, the 100G module is far more efficient at utilizing the available bandwidth:
- 40G: Fixed at 4x10G NRZ. Limited to 40 GB of total bandwidth.
- 100G: Fixed at 4x25G NRZ. By increasing the electrical data rate per lane from 10G to 25G, the overall bandwidth is increased by 150% in the exact same physical space. This leap in efficiency conserves valuable rack space.
2. Fiber Cabling and Breakout Flexibility (The Installation)
This is where 100G offers tremendous value in network architecture:
- MPO Cabling: Both 40G SR4 and 100G SR4 Multimode transceivers require 8 fibers (4 for transmitting, 4 for receiving) and utilize the MPO connector.
- Breakout Capability (The 4x Advantage):
- 40G: Only supports breaking out to 4 x 10G SFP+ connections.
- 100G: Supports breaking out to 4 x 25G SFP28 connections.
- Value: Since 25G is the current standard server access speed, the 100G breakout capability allows a single QSFP28 port to connect four high-speed servers or access switches, simplifying and modernizing network design.
3. Power Consumption and Heat Dissipation (The Operational Cost)
When dealing with hundreds of ports, power and cooling are the biggest long-term expenses.
- Key Fact: Due to superior integration and advanced chip design, 100G QSFP28 transceivers are dramatically more power-efficient per gigabit than 40G QSFP+.
- The Metric: Its Watts per Gigabit ratio is much lower. This translates directly into reduced cooling requirements and significant savings on electricity over the module’s lifetime, an essential consideration for high-density data centers.
4. Cost Per Bit (The Financial Metric)
The single most misleading metric is the absolute price. You must evaluate the Total Cost of Ownership (TCO) / Cost per Gbit/s.
| Feature | 40G QSFP+ | 100G QSFP28 | Winner |
| Lane Speed | 10 Gbps | 25 Gbps | 100G |
| Power/Gbps | Higher | Lower | 100G |
| Breakout | 4 x 10G SFP+ | 4 x 25G SFP28 | 100G |
| Future Proofing | Low | High (Path to 400G) | 100G |
Conclusion: Today, the 100G QSFP28 standard has reached cost maturity. When accounting for the density, power savings, and the ability to handle future traffic growth, 100G is now often the cheaper solution on a cost-per-bit basis.
When to Deploy Which Module
When to Stick with 40G QSFP+
Deploying 40G QSFP+ today is only advisable in highly specific, limited scenarios:
- Legacy Extension: You must extend an existing, fixed-capacity 40G link, and the destination hardware cannot support 100G.
- Inventory Reduction: You have a massive existing inventory of 40G equipment and modules that must be utilized before a final shift to 100G.
For nearly every new deployment, 40G is an obsolete standard.
Why 100G QSFP28 is the Modern Standard
The 100G QSFP28 is the current cornerstone of scalable data center design for three core reasons:
- Scalability and Density: It allows five times the bandwidth in the same physical switch space as the old 10G SFP+ standard.
- Foundation for 25G: By enabling 4 x 25G breakouts, it perfectly matches the modern server access speed of 25G.
- Future-Proofing: It shares its electrical foundation with newer, higher-speed standards (like 200G and 400G QSFP-DD), ensuring a clear upgrade path.
Compatibility and Reliability
A common concern during migration is the cost and reliability of transceivers. Using high-quality, third-party, MSA-compliant modules eliminates the financial barrier without sacrificing performance.
PHILISUN provides transceivers that are not only built to the exact Multi-Source Agreement (MSA) standards but are also subjected to rigorous, real-world testing.6 We ensure complete compatibility with major OEM platforms (Cisco, Juniper, Arista, etc.) through precise EEPROM coding.
Our commitment to quality means that every PHILISUN QSFP28 module is fully tested in target equipment to guarantee seamless integration, low error rates, and stable operation in your critical network infrastructure.
Conclusion: Making the Future-Proof Decision
The transition from 40G QSFP+ to 100G QSFP28 is not merely an upgrade; it is a shift to a more efficient, cost-effective, and scalable architecture. The benefits of lower power consumption, superior density, and greater breakout flexibility cement 100G as the necessary foundation for any modern, high-performance network. Don’t invest in a dying standard—invest in the future.
Final Expert Tip: Always check the transceiver’s DDM (Digital Diagnostic Monitoring) readings for power stability and temperature. PHILISUN transceivers fully support DDM, giving you a reliable, real-time tool to monitor module health and ensure your network’s long-term stability.
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