Navigating 100G Network Upgrades: Comparing QSFP-100G-SR1.2 and 100G BiDi Transceivers

As organizations strive to meet the demands of increasing data traffic, the choice of optical transceiver modules has become a pivotal consideration in network infrastructure upgrades. Particularly, the selection between the Cisco Compatible 100GBASE-SR1.2 QSFP28 transceiver—a module that leverages existing multimode fiber setups—and the more recent 100G BiDi variant presents a dilemma. This article aims to clarify the key differences and assist network professionals in making an informed decision based on their specific requirements.

What Is QSFP-100G-SR1.2 Module？

The QSFP-100G-SR1.2 transceiver is a high-performance, pluggable optical module that provides a seamless upgrade to 100 Gigabit Ethernet connectivity for data center operators looking to leverage their existing 10 Gb duplex Multi-Mode Fiber infrastructure. Equipped with a duplex LC connector interface, this transceiver is designed for short-reach applications and adheres to the QSFP28 Multisource Agreement (MSA) and IEEE 802.3bm CAUI-4 electrical interface standards. It features advanced digital diagnostic functions accessible through an I2C interface, as outlined by the QSFP28 MSA, letting users monitor real-time operational parameters. Additionally, it is capable of connecting with a 400 Gbps SR4.2 BiDi transceiver in a 4x 100G-SR1.2 breakout mode, further extending its versatility and offering a cost-effective solution for data centers looking to transition from 10G to 100G without overhauling their existing MMF cabling systems.

The Differences Between 100G-BIDI and QSFP-100G-SR1.2

The difference between 100G-BIDI and QSFP-100G-SR1.2 is mainly in the number of optical lanes and the modulation solution. 100G-BIDI uses two optical lanes, one for each direction, over a duplex LC multi-mode fiber. QSFP-100G-SR1.2 uses four optical lanes, two for each direction, over the same fiber. 100G-BIDI uses NRZ (Non-Return-to-Zero) modulation, which means each bit is encoded as a single symbol. QSFP-100G-SR1.2 uses PAM4 (Pulse Amplitude Modulation) modulation, which means each symbol encodes two bits. PAM4 enables higher data rates with lower baud rates but also introduces more noise and complexity. Both 100G-BIDI and QSFP-100G-SR1.2 are compliant to IEEE802.3bm 100GBASE-SR4 standard. The main advantage of 100G-BIDI is that it can reuse the existing 40G-BIDI infrastructure and reduce the fiber cabling cost. The main advantage of QSFP-100G-SR1.2 is that it can interoperate with 400G-SR4.2 and provide a future-proof solution for higher bandwidth demand.

Another difference between 100G BiDi and 100G-SR1.2 is the FEC (Forward Error Correction) used. 100G-BIDI (100G-SRBD) modules have been widely deployed for 100G operation over duplex MMF and use a FEC implementation that was developed prior to the IEEE standardization of KP-FEC for 50G PAM-4 based modules. Because of the differences in FEC implementation, 100G-SRBD and 100G-SR1.2 modules are not interoperable with each other.

How to Choose the Right Module

When you need to choose between two QSFP28 modules, the QSFP-100G-SR1.2, and the 100G BiDi, the following factors will help you make a decision:

Fiber Resources

The QSFP-100G-SR1.2 module typically requires 12-fiber cabling (with an MPO/MTP connector), which means it utilizes more fiber resources. The 100G BiDi module, on the other hand, can achieve 100G transmission over a single pair of LC duplex fibers, thus reducing the amount of fiber required, making it suitable for environments with limited fiber resources.

Link Distance

The QSFP-100G-SR1.2 module commonly supports up to 100 meters (with OM4 multimode fiber) or 70 meters (with OM3 multimode fiber). The distance supported by 100G BiDi modules may vary by manufacturer, but they are usually designed for distances of 100, 150 meters, or more, allowing BiDi modules to provide connections over longer distances without switching to single-mode solutions.

Cost

Although the BiDi module has advantages in reducing fiber resources, it might be more expensive than the standard SR1.2 module. Comparing the costs of modules should also consider the costs of fiber cabling; if the fiber is already abundantly laid out, the standard SR1.2 might be the more economical choice.

Scalability and Upgrade Plans

Consider your future scalability and upgrade plans. If future network expansions may require additional fibers, using BiDi could offer greater flexibility.

Therefore, when choosing a module, consider the fiber resource situation, costs, device compatibility, and future network upgrade needs comprehensively. For situations with tight fiber resources and a need to save on fiber cabling costs, the 100G BiDi is a good choice; however, if fiber resources are abundant or ease of operation and cost are the main considerations, then selecting the 100G SR1.2 is also appropriate. It is advised to contact the network equipment supplier or a professional optical module provider for more detailed technical support and advice.

Conclusion

To conclude, the choice between the QSFP-100G-SR1.2 and the 100G BiDi modules should be guided by factors such as available fiber resources, desired link distances, costs, and future network scaling. While the 100G BiDi shines in fiber-scarce environments, the QSFP-100G-SR1.2 offers benefits for those with abundant fiber infrastructure or who require compatibility with higher bandwidth systems. It is essential to weigh both immediate needs and long-term objectives before making a selection. For tailored advice, reach out to network equipment vendors or specialists in the field who can provide insights tailored to your unique situation, ensuring your network remains robust and future-ready.