QSFP56 vs QSFP28: 200G/100G Module Selection and Future-Proofing Your Network

Choosing between QSFP56 and QSFP28 modules can feel like you are at a tech crossroads. With data centers pushing for faster speeds and more efficiency, the right choice is becoming even more critical. Which provides the best performance, cost, and future-proofing? This article discusses the main differences, so you’re more confident in deciding between the 200G and 100G solutions while positioning your network for a seamless evolution in innovation moving forward.

From QSFP+ to QSFP56: Understanding the Core Driver Behind the 200G Revolution

The transition from QSFP+ to QSFP28, and now to QSFP56, represents a huge jump in speed and capacity for networks. QSFP+ modules initially supported a 40G connection, with 4 lanes of 10G. Following the QSFP+ module was QSFP28, which increased the speed to 100G with the speed per lane increasing to 25G.

Now, the QSFP56 has doubled the lane speed to 50G, which yields a 200G connection, and all this while keeping the same reliable form factor. Networks are moving to 200G from 100G (QSFP28) for a variety of reasons, including the global data explosion and the demand for bandwidth efficiencies.

Furthermore, QSFP56 provides such increases in speed while offering backward compatibility with current infrastructure. This ultimately enables data centers to expand capacity within existing costs and physical space. As an approach to future-proofing their high-speed networks, QSFP56 modules will be a critical component in the expansion.

Decoding the Technology: QSFP56 vs QSFP28’s Fundamental Differences

QSFP56 represents an impressive evolution from 100G to 200G performance while still maintaining an identical physical footprint to QSFP28 modules. This is possible due to two key technologies: advanced signal modulation and greater packaging density.

The first breakthrough is in the signal modulation. QSFP56 utilizes PAM4 modulation, which encodes two bits of data per symbol, effectively doubling the data transmission rates when compared to the NRZ scheme used in the QSFP28, which encodes one bit of data per symbol.

You can think of it this way: with an NRZ scheme, you are encoding a simple on-off Morse code signal. With PAM4, you code a facet of a more complex language that effectively doubles the amount of information in each signal pulse.

Secondly, QSFP56 modules utilize a greater degree of packaging density. QSFP28 modules include four lanes, with each lane supporting data transmission rates of 25G each. QSFP56 doubles the lane speed to 50G per lane, which allows the total bandwidth of each module to be 200G, all while using the same number of lanes and form factor.

Think of it like this: the total number of cars on the four-lane highway remains the same, but the cars can simply go twice as fast as before. You could also begin to think of QSFP56 as a highway with multiple on-ramps.

Coupling these technologies provides faster data transfer while maintaining compatibility with the existing infrastructure. The combination provides data centers the ability to increase bandwidth without physically expanding the data center footprint and not increasing the associated costs.

The following sections of this document will unpack this technical leap further and provide context for how it impacts the next generation of high-speed networking.

Feature

This table presents a simple visual summary of how QSFP56 doubles the data rate and enhances modulation complexity, all within the same form factor as QSFP28, while outlining the density and compatibility benefits fundamental to careful network upgrade planning.

The Game-Changer: PAM4 vs NRZ Signal Modulation

At the core of data transmission technology is signal modulation, which decides how bits will be encoded into electrical or optical signals. In high-speed networking, two major signal modulation schemes exist: Non-Return to Zero (NRZ) and Pulse Amplitude Modulation 4-level (PAM4). This is an important distinction to make for truly understanding how we go from the performance of QSFP28 to QSFP56.

NRZ has been utilized in QSFP28 modules. In NRZ, data is encoded in one of two voltage levels, with one level representing a binary ‘1’ and another representing a ‘0’. Think of a manually operated light switch.

In the light switch example, the switch being ‘on’ or ‘off’ encodes one bit of information per clock cycle. Operated this way, NRZ is understood as a reliable encoding option that is less susceptible to noise but limited because of the amount of data transmitted per symbol.

PAM4 (the encoding standard in QSFP56 DD modules), however, is more complex but provides for increased data density and rate as it conveys 4 levels of data amplitude. Instead of a simple switch, think of a dimmer switch with more than two positions.

Each level of brightness will represent a two-bit combination of status (00, 01, 10, 11) on one clock cycle. What PAM4 does is use two bits of data per symbol, which doubles the data rate of NRZ. This means, as an example, the QSFP56 will transmit 50G per lane, which is double the lane speed of QSFP28, which operates at 25G per lane.

While there are clear advantages with PAM4 by way of increased reliability, there are also difficulties associated with increased noise and jitter (timing variation that can compromise data). Because PAM4 is density dense,

It means signal processing has to be more exact, and error correction has to be more complex and dense, therefore increasing design difficulties as well as cost. Regardless of these increased complexities of PAM4, the real advantage is that PAM4 has allowed for doubled the bandwidth throughput INTO a device without changing the physical size of the module or doubling the number of lanes.

This is a major leap in a world where increased capacity is necessary. PAM4 is further behind the increased capacity of QSFP56 DD to push 200G performance through a port that uses the same familiar port form factor as a QSFP28 module.

To summarize, the differences between NRZ and PAM4 signal modulation provide the key enabling technology for a QSFP56 device vs. a QSFP28. NRZ is simple, cost-effective, and reliable,

But PAM4 gives all users the additional data rates to supply vast amounts of data to satisfy the growing data demand of today’s data centers, all while managing the added complexity of the signals that would accommodate that demand. Understanding the differences in modulation is probably very important in your decision-making when selecting a high-speed module.

Density and Compatibility: The Evolution of Physical Form Factors

The transition from QSFP28 to QSFP56 not only enhances speed, but it also fundamentally changes port density and form factors of connectivity. The dimensions of the QSFP form factor have remained unchanged; however, QSFP56 introduces the concept of Double Density (DD), which allows for additional connection lanes without increasing the physical form factor.

QSFP28 modules traditionally offer four lanes of connectivity with a 25G capacity, for a total throughput of 100G. With QSFP56-DD, eight lanes are housed in approximately the same form factor, offering 50G bandwidth per lane. Think of the form factor as a zipper that has moved from four teeth wide to eight teeth wide: it doubles the capacity down the same path without changing the overall length of the zipper!

The double-density design maximizes the bandwidth capabilities and port density of the switch, while considering the number of connections that can be placed in each rack space in the data center, which is key to a high-density data center! While the QSFP56-DD connector is a higher-density option compared to the QSFP28 specification, it is still a QSFP form factor and will allow for interoperability and eventual migration.

Network operators can take their time migrating through the use of adapters and backward-compatible ports into a fully upgraded optical transport hierarchy. Essentially, the user will emerge from an existing investment with minimal operational disruption during the gradual transition of speeds, upgrading to this advanced upgraded form factor.

The QSFP56-DD connections will allow you to add lane counts and speed, while maintaining form factor and compatibility, which opens the door for a lower-cost capacity upgrade, with the full intent of future-proofing the network as traffic continues to grow.

To summarize, QSFP56 and QSFP28 provide evidence of the evolution of physical form factors from speed improvements in spite of spatial efficiencies. The double density of QSFP56-DD will arm networks with a formidable means to advance scaling connectivity while managing integration concerns into the performance criteria when organizing the next generation of data center infrastructure!

Making the Right Choice: A Practical Selection Guide for Your Network

When upgrading your network infrastructure, choosing between QSFP56 and QSFP28 can feel overwhelming, considering technical specifications, costs, and compatibility, if that applies. This section or part of our typical format will help you understand and process the practical factors to weigh the benefits and limitations of each option transparently, so that you can choose the module that fits your network performance needs and your budget.

 Cost-Benefit Analysis: The Economics of QSFP56 vs QSFP28

To accurately evaluate the true cost of the QSFP56 vs. QSFP28 modules, it’s necessary to go beyond just the sticker price to the cost per bit, or the effective cost for every unit of transmitted data. While QSFP56 modules are usually priced higher than the sticker price, they are delivering double the bandwidth (thereby lessening the effective cost per gigabit).

Factor in the total cost of ownership (TCO), which is not only the cost of the module, but also factors in the cost of the consuming power, cooling, and any costs related to network upgrades. The higher speed of the QSFP56 could potentially lead to reducing the number of ports and physical connections needed, therefore reducing any expenses related to cabling and operational costs over time.

In deployments where traffic density is high, QSFP56, with greater bandwidth per port, means network architects can reduce physical hardware (consolidation). Less physical hardware translates to less rack space, and power delivery, as well as cooling considerations.

Alternatively, QSFP28 will still remain a valid option, provided TCO is factored in to make it the most cost-effective decision—especially with its performance being more affordable within 100G existing applications.

The decision to determine if the QSFP56 price outweighs the QSFP28 cost really comes down to the growth of your network and your ultimate goals. The investment in a QSFP56 will justify its cost with the immediate expenditure, but the optimized savings and scalability in the specifications of the equipment will be apparent to you throughout its lifecycle.

Careful consideration of the economic factors will prevent you from unnecessarily overextending your network investment to receive a reasonable return.

Case Study: A Data Center’s Strategic Upgrade from 100G to 200G

A medium-sized company increasingly faced bandwidth bottlenecks from its expanding datacenter. Existing QSFP28-driven 100G links were unable to keep up with the traffic generated by cloud services and virtualized workloads.

Recognizing the need for a bandwidth upgrade strategy, the IT staff embarked on a plan to introduce QSFP56 modules in phases to create a 200G trail.

In the project planning stage, the entire audience was engaged in a compatibility audit. It was critically important to identify QSFP56 modules that interoperated with legacy equipment. This meant identifying compatible switches and the appropriate cabling.

The IT staff leveraged available fiber, but some links had to be upgraded to support the PAM4 modulation QSFP56 utilization.

Cabling presented logistical challenges that required careful mapping and a phased swap-out strategy to reduce downtime. The use of breakout and hybrid cables enabled a gradual insertion of new, higher-density QSFP56-DD modules without taking the network offline.

Return-on-investment (ROI) recommendations indicated the immediate value from the transition to 200G. Throughput doubled, latency decreased, and server utilization improved. Significantly, the performance improvement translated into improved application performance and greater user satisfaction.

Finally, with the implementation of density, the number of switches was reduced, leading to less power consumption and less maintenance.

As this case study reveals, with a well-planned project focused on compatibility, building on recent research, and the phased rollout, the user organization was able to respond to growing bandwidth needs while managing the complexity of introducing next-generation networking speed.

This case study further illuminates the challenge of balancing technical requirements with operational realities, resulting in a successful transition from QSFP28 to 200G performance.

The Future of High-Speed Networking: Trends Beyond 200G

As networks advance to even more extreme speeds of 400G and even 800G, the QSFP56 will be a critical standard. Modulation formats and double-density, double-data rate were developed as part of these advancements at standard networking rates.

In addition, when you consider the potential for deployment in data centers with a growing demand for 200G, the QSFP56 module will provide the building blocks for scalable and flexible networking architectures.

The next generation of modules in the industry will also reflect next-generation standards based on evolving form factors like OSFP (Octal Small Form-Factor Pluggable) and COBO (Consortium for On-Board Optics) to push bandwidth above 400G while providing even lower power and denser design.

These form factors will again learn from the double-density design of the QSFP56-DD while focusing on heat dissipation as well.

Realistically, QSFP56 will provide a path to larger form factors compatible with the 400G QSFP-DD module. It will not only allow network architects the opportunity to utilize a familiar port interface while planning for future 400G integration, but it will also protect their investment in an evolving standard capable of migrating to next-generation modules.

Overall, learning about the QSFP56 will inform you of developments in the industry to continue evolving signal processing, packaging, and form factors for high-speed networking—a flexible platform with an enormous portion of capacity and low complexity and cost.

 Conclusion

It is important to understand the differences between QSFP56 and QSFP28 so you can make the right decisions when upgrading your network. Quite simply, QSFP56 adds a layer of complexity in modulation and includes a double-density design that allows for a significant bandwidth increase while maintaining the physical form factor of QSFP28.

The enhancements in QSFP56 are ideal if you are considering network upgrades to scale your capacity in data center networks.

Making intelligent investments in technologies in data center networking allows a network operator to plan and accommodate the increased demand for performance without replacing the entire infrastructure, which can be costly.

Knowing you have the benefit of the advice of an infrastructure professional can help develop solutions that you can rely on to plan and take into account costs, compatibility/risk, and future capability.

If you would like flexibility and foresight in your network now and in the future, QSFP56 and QSFP28 are your new standard options for the high bandwidth, speed, and capability needed to keep up with increased consumer, business, and technology demands.

FAQs

Q1: Why does QSFP28 sometimes have a higher power draw than QSFP56?
QSFP28 utilizes NRZ modulation to obtain 25G per lane of transfer, which is much easier to implement but uses a lot of electric power to ensure the integrity of the signal as the transmission distance grows.

Environmentally friendly QSFP56 utilizes PAM4 modulation to obtain 50G per lane of transfer, which doubles the density of the data while enhancing the efficiency of electric circuitry through improved signal integrity. In fact, despite reasonably directing 50G per lane of transfer, QSFP56 modules require less power than traditional 25G lanes of transfer in QSFP28 modules.

Q2: What does QSFP56 have in common with 200GBASE-SR4?
Most QSFP56 modules provide support for edge cases of 200GBASE-SR4 standards, which refers to 200G of transmission over short distances within multi-mode fiber processing or transmission over the same number of lanes in QSFP format.

In other words, 200GBASE-SR4 specifies 200G transmission over four lanes at 50G. Because QSFP56 transmits at 50G per lane, they are the natural choice for 200GBASE-SR4 modules to achieve compatibility/speed requirements for high speeds found in switching environments in data centers.

Q3: Will QSFP28 transceivers work in a QSFP56 port?
Based on the manufacturer, the answer is likely yes—most QSFP56 ports also have backward compatibility with QSFP28 transceivers. A port designed for QSFP56 support typically enables backward compatibility in front-facing configurations, allowing network operators to mix the transceivers in modules during an upgrade.

This allows operators to transition without having to replace hardware all at once.

All of these answers help to address the most common questions regarding performance, compatibility, and power efficiency differences while clarifying the capabilities of QSFP56 and QSFP28 as acceptable upgrade options for enhanced speeds and networking capabilities.