400G SR4 vs. 400G SR8: What’s the Difference?
The rapid growth in data traffic and the need for higher-speed connectivity in data centers have led to the development of advanced optical transceivers. Among them, 400G SR4 and 400G SR8 are two prominent solutions designed to meet the increasing demand for higher throughput. However, choosing the right one for your network can be challenging. In this article, we'll explore the key differences between 400G SR4 and 400G SR8 to help you make an informed decision.
What Is 400G SR4?
400G SR4 (Short Reach 4) is a high-speed optical transceiver that supports 400 Gbps over multimode fiber (MMF). It uses 4 parallel lanes for both transmitting (TX) and receiving (RX) data, with each lane operating at 100 Gbps to achieve a total of 400 Gbps. The technology employs multimode fiber (MMF), typically OM3 or OM4, which supports shorter distance communication typically up to 100 meters for OM4 fiber. The interface uses an MPO/MTP (Multi-Fiber Push-On/Pull-Off) connector, which contains 12 or 16 fibers. In the SR4 configuration, 8 of these fibers are active (4 for transmitting and 4 for receiving), while the remaining fibers may be unused or reserved for future use.
FS 400G SR4 Transceivers
The FS 400G SR4 transceivers feature compact OSFP, QSFP112, and QSFP-DD form factors, making them ideal for high-speed data centers and high-performance computing networks. Key selling points include support for 400Gbps transmission rates, low power consumption, high-density, and multimode fiber connectivity. These transceivers offer an efficient and cost-effective solution while being compatible with existing 400G/100G infrastructure, ensuring seamless upgrades and exceptional performance.
The following picture shows the 800G-to-two 400G link for Switch-to-Switch of QSFP-DD 400G SR4.
| OSFP-SR4-400G-FL | QSFP112-SR4-400G | QDD-SR4-400G | |
| Center Wavelength | 850nm | 850nm | 850nm |
| Connector | MTP/MPO-12 | MTP/MPO-12 | MTP/MPO-12 |
| Cable Distance (Max.) | 30m/50m@MMF | 50m@MMF | 60m/100m@MMF |
| Modulation | 4x 106.25G PAM4 | 4x 100G PAM4 | 8x 50G PAM4 |
| DSP | 7nm DSP | Broadcom 7nm DSP | Maxlinear |
| Power Consumption | ≤8.5W | ≤9W | ≤8W |
| Transmitter Type | VCSEL | VCSEL | VCSEL |
| Packaging Technology | COB | COB | COB |
| Application | InfiniBand 800G to 2x400G Breakout |
Data Center | Data Center 400G to 2x200G Breakout 400G to 4x100G Breakout |
What Is 400G SR8?
400G SR8 (Short Reach 8) is another high-speed optical transceiver designed for data centers but utilizes 8 parallel lanes, each operating at 50 Gbps. The total bandwidth provided by 400G SR8 is also 400 Gbps, similar to 400G SR4. However, SR8 can support longer distances up to 70 meters with OM3 MMF and 100 meters with OM4 MMF. Moreover, it offers two variants of optical lane arrangement. One variant utilizes the 24-fiber MPO, configured as two rows of 12 fibers, while the other interface variant employs a single-row MPO-16.
The 400GBASE-SR8 offers flexible fiber shuffling capabilities, supporting configurations of 50G, 100G, and 200G. In addition, it enables speed breakouts tailored for a variety of applications such as computing, storage, flash, GPU, and TPU. The 400G-SR8 QSFP-DD/OSFP transceivers are highly versatile, functioning as 400GBASE-SR8, 2x200GBASE-SR4, 4x100GBASE-SR2, or 8x50GBASE-SR connections as needed.
FS 400G SR8 Transceivers
FS provides both QSFP-DD and OSFP form factor 400G SR8 transceivers which are compatible with most brands such as Arista and Generic. FS 400G SR8 transceivers facilitate seamless breakout to 8x SFP56 50G SR optics, enabling the creation of 400G connections to meet the escalating demands for consumer data rates. Moreover, this breakthrough architecture is achieved while leveraging existing fiber cable infrastructure, thereby optimizing cost-effectiveness.
| QDD-SR8-400G | OSFP-SR8-400G | |
| Center Wavelength | 850nm | 850nm |
| Connector | MTP/MPO-16 | MTP/MPO-16 |
| Cable Distance (Max.) | 70m/100m@MMF | 100m@MMF |
| Modulation | 8x 50G PAM4 | 8x 50G PAM4 |
| DSP | Inphi DSP | Inphi DSP |
| Power Consumption | ≤10W | ≤10W |
| Transmitter Type | VCSEL | VCSEL |
| Packaging Technology | COB | COB |
| Application | Data Center 400G to 8x50G Breakout |
Data Center 400G to 8x50G Breakout |
400G SR4 vs. 400G SR8
When choosing between 400G SR4 and 400G SR8 optical transceivers, several factors need to be considered, including performance, infrastructure requirements, use cases, and cost. Below is a comparison of the two:
| 400G SR4 | 400G SR8 | |
| Lane Configuration | Use 4 parallel lanes at 100 Gbps each | Use 8 parallel lanes at 50 Gbps each |
| Fiber Count | 8 fibers (4 transmit and 4 receive) | 16 fibers (8 transmit and 8 receive) |
| Connector Type | Typically uses MPO-12 connectors, as it needs 12 fibers (8 used, 4 spare) | Typically uses MPO-16 connectors, which aligns with its requirement for 16 fibers) |
| Distance | Typically supports up to 100 meters with OM4 MMF | Typically supports up to 70 meters with OM3 MMF and 100 meters with OM4 MMF |
| Applications and Use Cases | Ideal for shorter interconnects within data centers and environments where infrastructure already supports OM4 fibers | Suitable for similar applications as SR4 but offers more flexibility with older OM3 MMF infrastructure due to its ability to perform well over slightly longer distances with lower-grade multimode fibers |
| Cost | Generally, fewer fibers can translate to lower overall infrastructure costs | The need for more fibers could increase costs, but it offers more flexibility in certain deployment scenarios |
Pros and Cons
To make an informed decision between 400G SR4 and 400G SR8, it’s crucial to weigh their respective advantages and disadvantages. Below, we outline the key pros and cons of each:
| 400G SR4 | 400G SR8 | |
| Pros | High data rate per lane (100 Gbps) | Greater lane granularity |
| Simpler infrastructure for networks already using 100 Gbps lanes | Potentially lower power consumption and reduced heat dissipation | |
| Ideal for high-performance computing environments | Better scalability for varying bandwidth needs | |
| Cons | Lower scalability per port compared to SR8 | Higher complexity in the network infrastructure due to more lanes |
| Potentially higher heat output due to higher lane speed | May require more sophisticated equipment to manage eight lanes |
Conclusion
While 400G SR4 and 400G SR8 provide high-speed connectivity solutions for modern data centers, their choice depends on your specific infrastructure and requirements. SR4 may be more cost-effective and simpler to deploy due to fewer fibers, making it suitable for new installations. On the other hand, SR8's compatibility with older multimode fiber types and a slight reach advantage make it a versatile choice for existing setups and specific scenarios.
Evaluating your network's current and future needs, considering factors like port density, power consumption, and infrastructure complexity, will guide you to the right choice. When in doubt, please contact us for technical support and consult with FS optical networking experts who can provide insights tailored to your unique situation.
Remember, both 400G SR4 and 400G SR8 are cutting-edge technologies designed to propel your network into the future—choosing the right one will set you on the path to optimal performance and scalability.
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