OSFP vs. OSFP-XD: 1.6T Transceivers Form Factor Comparison

With the widespread application of large language models (LLMs) and the rapid advancement of supercomputing technology, bottlenecks in information processing and communication have become increasingly evident. To address this challenge, 1.6T optics, a high-bandwidth network connectivity solution, has emerged, suitable for hyper-scale data centers, cloud computing, and other demanding scenarios. 1.6T optics primarily feature two form factors: OSFP and OSFP-XD. This article will delve into 1.6T transceiver form factors' characteristics and design differences.

Introduction of 1.6T OSFP

The OSFP (Octal Small Form-factor Plug), has become the preferred form factor for high-speed applications such as artificial intelligence and HPC networks as it offers future expansion with more channels, more space for components, and higher power dissipation capabilities. The OSFP has widely been adopted for pluggable optics in both 400G (with an 8x50 Gb/s host interface) and 800G (with an 8x100 Gb/s host interface) applications.

In 2022, the OSFP MSA released the OSFP1600 specification. OSFP1600, also called 1.6T OSFP or OSFP 224G, offers 8x200G host interfaces and breaks through the limits needed to achieve electrical performance, all while ensuring mechanical reliability and full backward compatibility with 400G/800G OSFP.

The 1.6T OSFP modules achieve a total bandwidth of 1.6T through 8 channels, each providing 200Gbps. This design allows for higher total bandwidth with fewer channels, improving data transmission efficiency. The OSFP 224G has an integrated heatsink to optimize system performance, becoming an ideal choice for hyperscale data centers, supercomputing, and HPC networks.

Introduction of 1.6T OSFP-XD

Although the OSFP1600 supports future switch silicon with 200 Gb/s electrical lanes, there is significant interest in 1.6 Tb/s optical transceivers within the 100 Gb/s electrical lane ecosystem. The OSFP-XD ('eXtra Dense') form factor was developed to address this demand. By increasing the number of electrical lanes from 8 to 16, the OSFP-XD provides 1.6T density with 16 lanes at 100 Gb/s and is poised to offer 3.2 Tb/s density with 16 lanes at 200 Gb/s in the future.

The OSFP-XD is primarily designed with several key objectives: high-power compatibility, copper cable support, and port density optimization. 1.6T OSFP-XD transceivers support up to 40W for future 1600-ZR and 3200G optical transceivers, ensuring stable high-performance data transmission. It is compatible with 100GBASE-CR1 standard passive copper cable solutions (DAC), meeting various connectivity needs. Additionally, 1.6T OSFP-XD transceivers enable 32-ports in a 1RU chassis and 64 ports in a 2U chassis, greatly enhancing space utilization and system expansion capabilities.

Design Differences Between OSFP and OSFP-XD

The OSFP 224G and 1.6T OSFP-XD modules differ not only in appearance but also in their internal structures and technologies.

Mechanical Details

Compared to traditional OSFP modules, the OSFP-XD slightly extends the length of the module. The OSFP-XD solution utilizes the well-known method of adding a second row of contacts on the internal PCB or the card within the module to double the number of high-speed electrical signals in the module.

To simultaneously accommodate high-power optical and dense copper solutions, the specification for OSFP1600 and OSFP-XD will define separate but compatible heatsink specifications for optical and copper modules, allowing module designs to independently optimize key characteristics for each implementation. Compared to OSFP modules, OSFP-XD modules have a volume that is 20% higher (15.5 millimeters). For passive DAC applications, the internal volume has increased by more than 12%.

The OSFP-XD module will feature a 1.2-millimeter thick card to support a 200Gb/s electrical interface, reduce routing complexity, and enable robust power distribution. Due to the increased card thickness and module height, OSFP-XD is incompatible with existing OSFP form factors. To prevent any damage to the OSFP-XD ports, the OSFP-XD cage will incorporate a keying feature to prevent OSFP modules from being inserted into OSFP-XD ports.

Optical PMD Block Diagrams

The Physical Medium Dependent (PMD) sublayer defines the process of transmission and reception of individual bits on the physical medium. The following two images illustrate the block diagram for the OSFP1600 and OSFP-XD optical PMD for 1600G, showing the differences in the physical connection between the 1.6T transceiver form factors.

Conclusion

The comparative analysis of this paper shows that OSFP and OSFP-XD each have their unique advantages and 1.6T trend for the future. To meet the industry tendency, FS currently offers 1.6T OSFP DAC cables, designed with 8x200G-PAM4. These cables feature ultra-high throughput and ultra-low power consumption, with power consumption under 0.1W.

The NVIDIA GB200 NVL72 rack-scale solution delivers 30X faster real-time LLM interface, attracting global enterprises with HPC networks. This system needs "copper interconnections," and the FS 1.6T OSFP DAC serves as an ultra-high-speed copper cable solution, ideal for NVIDIA GB200 NV72 rack-scale systems.