AI OSFP-RHS vs Standard OSFP: Thermal Design, Mechanical Differences and 800G/1.6T Applications

1. What Is Standard OSFP?

OSFP stands for Octal Small Form-factor Pluggable. It is a high-speed pluggable transceiver form factor designed for data center switches, routers and high-performance computing platforms.

Standard OSFP modules use an integrated heatsink as part of their mechanical package. The heatsink is attached to the module itself and provides a thermal path for transferring heat away from internal components toward the host system airflow.

Depending on the mechanical implementation, standard OSFP can use a closed-top or open-top integrated heatsink design. The exact heatsink structure, module dimensions and thermal performance depend on the applicable OSFP specification and product implementation.

Standard OSFP is used in high-speed networking systems supporting 400G, 800G and 1.6T optical connectivity. Depending on the module generation and application, it can support different optical technologies, including SR, DR, FR and coherent transmission.

Its integrated thermal structure makes standard OSFP a practical option for equipment designed around conventional pluggable transceiver cooling, where the module's heatsink is part of the replaceable optical component.

2. What Is OSFP-RHS?

OSFP-RHS stands for OSFP Riding Heat Sink. Unlike standard OSFP, the OSFP-RHS module does not include an integrated heatsink. Instead, it is designed to make thermal contact with a riding heatsink installed as part of the host equipment.

The module itself has a lower mechanical profile without the integrated heatsink. The host cage incorporates a dedicated structure that supports the riding heatsink and maintains the required thermal contact with the module.

This approach separates the optical module from the primary heatsink structure. The host platform can therefore integrate the thermal assembly into its own cooling architecture, subject to the mechanical and thermal requirements of the OSFP-RHS specification.

The riding heatsink may be implemented as part of an air-cooled host design or a compatible system-level cooling solution. OSFP-RHS does not automatically mean liquid cooling, and it does not guarantee lower operating temperatures without proper host thermal design.

3. OSFP-RHS vs Standard OSFP: Core Differences

The main difference between standard OSFP and OSFP-RHS is the thermal integration method. Both use the OSFP electrical interface family, but the module housing and host cage are designed differently.

The electrical and management specifications are aligned, but the mechanical structures are not interchangeable. The appropriate host cage must be selected for the module type.

4. Integrated Heatsink vs Riding Heatsink Architecture

Standard OSFP and OSFP-RHS use different approaches to remove heat from high-speed optical components. The distinction is especially relevant as module power and front-panel density increase in 800G and 1.6T network platforms.

In standard OSFP, the heatsink is integrated into the optical transceiver. Heat generated by the internal DSP, laser drivers, optical engine and other components is transferred through the module thermal structure to the integrated heatsink.

The host system supplies the required airflow and mechanical clearance around the integrated heatsink. Module thermal performance therefore depends on heatsink design, thermal contact inside the module, host airflow, inlet temperature and installed module density.

In OSFP-RHS, the module does not carry its own integrated heatsink. Instead, its designated thermal contact surface interfaces with the riding heatsink mounted in the host cage.

This separates the optical module from the main cooling structure. The equipment manufacturer can design the host-side heatsink and thermal arrangement around the overall switch or system architecture.

An OSFP-RHS design does not automatically dissipate more heat than standard OSFP. The final thermal result depends on the riding heatsink material, contact surface quality, contact pressure, thermal interface materials, airflow or coolant conditions and the module's actual power consumption.

5. Mechanical Structure and Host Cage Compatibility

Although standard OSFP and OSFP-RHS use the same family of electrical and management interfaces, their mechanical dimensions are designed for different host cages.

Standard OSFP uses a module package with an integrated heatsink. Its host cage provides the mechanical opening, retention features and clearance required by that package.

OSFP-RHS uses a module without an integrated heatsink and a dedicated host cage containing the riding-heatsink arrangement. The MSA defines different cage height, forward-stop position and bezel cutout geometry to match the RHS module.

The OSFP-RHS module also has a different forward-stop position to prevent full insertion into a standard OSFP cage. This mechanical keying arrangement helps prevent an incorrect module and cage combination.

The host PCB connector layout can remain the same while the mechanical cage and surrounding thermal assembly change. This is why electrical similarity should never be interpreted as mechanical interchangeability.

6. Electrical Interface, Management and Data Rate

OSFP-RHS is a mechanical and thermal implementation within the OSFP ecosystem. It does not define a different optical signaling method or aggregate bandwidth.

Standard OSFP and OSFP-RHS use the same electrical and management interface specifications within their corresponding speed grades. This allows both variants to support similar electrical lane configurations when designed for the same performance generation.

Depending on the product generation, OSFP-family modules can support different lane speeds:

Both standard OSFP and the corresponding RHS variants can support these performance generations when the specific module, cage and host platform follow the applicable MSA requirements.

The management interface provides module identification, monitoring and control functions. Depending on the implementation and supported CMIS version, diagnostic information can include temperature, voltage, optical transmit power, receive power and alarms.

7. OSFP-RHS Applications in AI Data Centers

AI data center infrastructure places increasing thermal demands on high-speed optical modules. Large switch systems may contain many 800G and 1.6T ports, creating concentrated heat loads around the front panel.

OSFP-RHS provides a way to integrate the transceiver thermal interface with the host equipment's cooling structure. This can be useful in platforms where the equipment manufacturer prefers a system-level heatsink instead of an integrated heatsink on every optical module.

Typical OSFP-RHS deployment considerations include:

• High-density 800G and 1.6T Ethernet switch platforms.

• AI training clusters with large numbers of high-speed optical connections.

• GPU networking systems with demanding host thermal requirements.

• Equipment designed around a shared or host-mounted riding-heatsink structure.

• Platforms with a qualified cooling architecture that integrates the transceiver thermal interface.

• Next-generation systems where optical module and host thermal designs are developed together.

OSFP-RHS is particularly relevant when the host manufacturer has a specific mechanical and thermal design for the optical module area. It should be selected as part of a complete platform design rather than as a standalone module upgrade.

8. Air Cooling and Liquid Cooling Integration

The riding-heatsink arrangement creates flexibility in how the host system manages heat, but it does not determine the cooling medium by itself.

In an air-cooled system, the host-mounted heatsink can transfer heat from the module into the airflow path. The final cooling performance depends on heatsink geometry, air velocity, inlet temperature, pressure drop and the thermal contact between the module and heatsink.

In a liquid-cooled system, the host thermal assembly may be designed to connect with a compatible cold plate or another liquid heat-removal structure. This requires coordinated mechanical dimensions, contact pressure, thermal interface materials and cooling-system qualification.

The distinction is important because OSFP-RHS is not itself a liquid-cooled optical module. It is a module form-factor arrangement that allows the host system to provide the riding heatsink.

Engineers should evaluate the complete thermal path instead of assuming that an RHS module will automatically operate at a lower temperature. Contact quality and host cooling capability are critical to stable operation.

9. Standard OSFP vs OSFP-RHS: Selection Considerations

The correct choice depends primarily on the mechanical and thermal architecture of the target switch or server platform. If a system is designed for standard OSFP cages, an OSFP-RHS module cannot be used as a direct replacement.

Before choosing a module, system designers should verify the cage type, module speed grade, host thermal structure, electrical interface, power consumption, supported CMIS revision and optical performance requirements.

10. C-LIGHT 800G and 1.6T OSFP-RHS Product Solutions

C-LIGHT provides OSFP and OSFP-RHS optical transceiver options for high-speed data center and AI network applications. Its 800G product portfolio includes both integrated-heatsink and RHS mechanical variants for selected optical configurations.

The 800G product examples show that the same optical configuration can be offered in different mechanical versions. For instance, 800G 2xFR4 is listed in both close-top and RHS versions, while the 2xDR4 family also includes close-top and RHS variants.

This distinction allows customers to evaluate the optical specifications separately from the host thermal and mechanical requirements.

11. Conclusion