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Navigating 100G Network Upgrades: Comparing QSFP-100G-SR1.2 and QSFP28-BIDI-100G

GeorgeUpdated at Jan 24th 20251 min read

As organizations strive to meet the demands of increasing data volume, the selection of the right optical transceiver modules has become a pivotal factor in network upgrades. Specifically, the choice between the Cisco-Compatible 100GBASE-SR1.2 QSFP28 transceiver—a module that utilizes existing multimode fiber infrastructure—and the newer 100G BiDi variant can present challenges. This article aims to highlight the key differences and help network professionals make informed decisions based on their unique network requirements.
What Is QSFP-100G-SR1.2 Module?
The QSFP-100G-SR1.2 transceiver is a high-performance, pluggable optical module that provides a cost-effective upgrade to 100 Gigabit Ethernet connectivity for data center operators looking to upgrade their existing 10G duplex Multi-Mode Fiber (MMF) 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.
In addition to its core features, the QSFP-100G-SR1.2 includes advanced digital diagnostic capabilities. These can be accessed through an I2C interface, allowing real-time monitoring of operational parameters, as outlined by the QSFP28 MSA.
The module is also flexible in its application. It can interoperate with a 400 Gbps SR4.2 BiDi transceiver in a 4x 100G-SR1.2 breakout mode, offering a seamless upgrade path for data centers. This solution allows users to leverage their existing MMF cabling systems without a complete infrastructure overhaul.
Form Type
QSFP-100G-SR1.2
Wavelength
850/910nm
Connector
Duplex LC
Media
MMF
TX Power
-6.2dBm~4dBm
Max Data Rate
106.25 Gbps
Max Cable Distance
70m@OM3/100m@OM4/150m@OM5
Transmitter Type
Marvell VCSEL
DDM/DOM
Supported
Minimum Receiver Power
-8.2dBm
Commercial Temperature Range
-10 to 60 ℃ (14 to 140°F)
CDR (Clock and Data Recovery)
TX & RX Built-in CDR
Protocols
QSFP28 MSA and IEEE 802.3bm CAUI-4
Inbuilt FEC
KP4 FEC
The Differences Between QSFP28-BIDI-100G and QSFP-100G-SR1.2
FS offers a series of BiDi modules with exceptional compatibility, enabling seamless integration into existing networks to simplify network upgrades and reduce overall deployment costs. Among these, the QSFP28-BIDI-100G and QSFP-100G-SR1.2 modules are representative solutions. Both modules use advanced optical technology, enabling high-speed data transmission while effectively addressing challenges in bandwidth, transmission distance, and cost efficiency.
Although both modules are designed for 100G data transmission, they differ significantly in terms of the number of optical channels, modulation technology, and performance advantages. The following will provide a detailed comparison of these two modules, analyzing their key features and applicable scenarios.
Optical Lanes and Transmission:
The QSFP28-BIDI-100G module utilizes Short Wavelength Division Multiplexing (SWDM) technology with four distinct wavelengths to achieve unidirectional 100G transmission over a single fiber. In contrast, the QSFP-100G-SR1.2 module employs two SWDM wavelengths to enable bidirectional communication over a single fiber, a duplex design that significantly impacts both the module's structural configuration and energy efficiency performance.
Modulation Technology: QSFP28-BIDI-100G uses a 4x25G NRZ modulation format, while SR1.2 uses a 2x50G PAM4 modulation format. The NRZ modulation format encodes each bit as a symbol, whereas PAM4 encodes two bits per symbol, enabling higher data rates but introducing increased complexity and noise.
Compliance and Interoperability: The FS BIDI module complies with the SWDM4 MSA (Multi-Source Agreement) protocol, while the SR1.2 adheres to the IEEE 802.3 standard. The QSFP28-BIDI-100G can reuse the FS 40G-BIDI infrastructure, reducing cabling costs. In contrast, the 100G SR1.2 BiDi supports future interoperability with 400G-SR4.2 to meet higher bandwidth demands. Notably, BIDI optical modules and SR1.2 modules are incompatible and cannot interconnect.
FEC (Forward Error Correction): QSFP28-BIDI-100G adopts KR4-FEC, while QSFP-100G-SR1.2 employs IEEE-standardized KP-FEC technology. This discrepancy renders them incompatible with each other.
In summary, the choice between QSFP28-BIDI-100G and QSFP-100G-SR1.2 depends on network needs, infrastructure, and future scalability considerations.
Feature
QSFP-100G-SR1.2
QSFP28-BIDI-100G
Number of Optical Lanes
One optical channel, two wavelengths, single-fiber bidirectional
Four optical channels, multiplexed for unidirectional transmission
Modulation Scheme
PAM4 (Pulse Amplitude Modulation)
NRZ (Non-Return-to-Zero)
Applicable Standard
IEEE 802.3bm 100GBASE-SR4
SWDM4 MSA
Advantages
Compatible with 400G-SR4.2, supporting future bandwidth expansion
Reuses existing 40G-BIDI infrastructure, reducing cabling costs
FEC Implementation
KP-FEC
KR4-FEC
How to Choose the Right Module
When deciding between the QSFP28 modules, the 100G SR1.2 and the QSFP28-BIDI-100G, the following factors should guide your decision:
Cost
First, prioritizing consideration of fiber cabling infrastructure costs is critical. The QSFP28-BIDI-100G demonstrates higher cost-effectiveness compared to the 100G SR1.2, delivering equivalent performance at a lower price point.
Scalability and Upgrade Plans
When planning for future scalability and network upgrades, consider the following scenarios:
Upgrading from 25G/40G to 100G: If your current network operates on 25G SR or 40G BIDI, transitioning to QSFP28-BIDI-100G is a cost-effective choice. This solution leverages existing multimode Duplex LC patch cables without requiring replacements.
Upgrading from 100G to 400G: If future 400G migration is planned, 100G SR1.2 technology is recommended. It ensures interoperability with 400G-SR4.2 standards, enabling seamless network evolution and smooth infrastructure upgrades.
This approach balances backward compatibility with future-proof readiness.
Conclusion
To conclude, the choice between QSFP-100G-SR1.2 and QSFP28-BIDI-100G should be based on factors such as existing fiber resources, target link distances, cost considerations, and future network scalability. The QSFP28-BIDI-100G, with its lower price point, 4x25G NRZ modulation, and support for duplex multimode fiber, is particularly suited for scenarios with limited fiber resources and a need for cost-effective solutions. Meanwhile, the QSFP-100G-SR1.2 leverages advanced 2x50G PAM4 modulation, offers a higher power budget, supports interoperability with 400G SR4.2 modules in breakout configurations, and is ideal for applications such as 100G-400G network upgrades and direct connections.
Regardless of your choice, FS's 100G optical transceivers deliver outstanding quality, reliable performance, and expert technical support. Both modules undergo rigorous testing to ensure seamless compatibility with major brand equipment and are equipped with FS Box real-time re-coding technology, enhancing configuration efficiency and reducing deployment time. Moreover, FS adheres to international quality and safety standards, offering customized solutions tailored to your specific needs. Choose FS for industry-leading products, exceptional compatibility, and dependable support, ensuring reliable network deployment and long-term scalability.