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Cisco 400G QSFP-DD Optical Transceivers Overview
Knowledge Base + 2024.01.23

Table of Contents

Introduction to QSFP-DD Optical Modules

Quad Small Form Factor Pluggable Dual Density (QSFP-DD) transceivers are a revolutionary advancement in data center technology. Supporting data rates up to 400G, these transceivers are designed to meet the growing demand for higher bandwidth in data centers. The QSFP-DD design is configured as an eight-channel electrical interface, enabling it to keep pace with the growing speed of networks and servers. By implementing Cisco 400G QSFP-DD optical transceivers, organizations can significantly optimize network performance, reduce latency, and enhance data transfer capabilities.

Cisco 400G QSFP-DD Transceivers Overview

Cisco 400G QSFP-DD optical transceivers demonstrate cutting-edge networking technology, delivering unrivaled data transfer speeds and performance. These high-capacity transceivers are a game changer in data centers, bringing unmatched speed and efficiency to the data transfer process. The 400G capacity of these QSFP-DD transceivers enables fast, seamless data flow to improve overall network productivity. Cisco's 400G QSFP-DD optical transceivers feature an eight-channel electrical interface design that further advances the data transfer process, reduces latency, and meets the rapidly changing need for increased bandwidth. By integrating these transceivers into their systems, organizations can significantly enhance their network performance and data transfer capabilities.

Features and Benefits

Cisco 400G QSFP-DD optical transceivers offer many features and benefits. They support modulation schemes such as NRZ, PAM4, ensuring reliable, high-speed data transmission. Their high energy efficiency reduces overall power consumption, making them an environmentally friendly choice for data centers. These transceivers also support backwards compatible QSFP28 and QSFP56 transceivers, providing flexibility and protection for your investment.

Supported Module Types

Cisco 400G QSFP-DD optical transceivers support a wide range of module types, including SR8, DR4, FR4, and LR4. This support enables organizations to select the most appropriate module based on their distance requirements and budget constraints.

Data Rates

Cisco 400G QSFP-DD optical transceivers support data rates ranging from 50G to 400G, providing versatility for different network requirements. With these data rates, organizations can easily handle large volumes of data, ensuring smooth, uninterrupted network operations.

Applications and Use Cases

Cisco 400G QSFP-DD optical transceivers are ideally suited for high-speed data center interconnects and can be used in a variety of applications. These include data center interconnects, enterprise networks, high-frequency trading, and cloud computing. In addition, with their backward compatibility, they are also suitable for incremental network upgrades, enabling organizations to transition to higher speed networks without significant upfront costs.

Technical Specifications

The technical specifications for Cisco's 400G QSFP-DD optical transceivers provide a detailed snapshot of their capabilities, enabling organizations to assess their suitability for specific applications.

Optical Parameters

Cisco 400G QSFP-DD optical transceivers excel in visual performance. They support a wavelength range from 850nm to 1310nm, depending on the specific module type. These transceivers also exhibit excellent optical power performance, with a maximum transmit power of +2.0 dBm and a minimum transmit power of -10.0 dBm. Receiver sensitivity ranges from -10.4 dBm to -13.6 dBm, providing high-quality signal reception. In addition, these transceivers maintain a high extinction ratio of approximately 3.5 dB, ensuring robust and reliable data transmission. With these optical parameters, Cisco's 400G QSFP-DD optical transceivers provide the visual performance necessary to support high-speed data transmission for the most demanding data center requirements.

Electrical Parameters

Cisco 400G QSFP-DD optical transceivers exhibit impressive electrical performance, making them well suited for high-speed data center applications. They typically operate from a 3.3V power supply, ensuring compatibility with standard data center power systems. They also achieve low power consumption, typically less than or equal to 10W in normal operation, helping to improve the energy efficiency of data center operations. The electrical interface is configured in an 8-channel configuration, supporting data rates up to 50 Gb/s per channel. With these electrical parameters, Cisco's 400G QSFP-DD optical transceivers deliver reliable performance that helps enable efficient and reliable data transmission in the data center.

Mechanical Specifications

Cisco 400G QSFP-DD optical transceivers are designed with advanced mechanical specifications to ensure seamless integration and robust performance in data center hardware configurations. These transceivers follow the QSFP-DD MSA form factor to ensure compatibility with a variety of network devices. Mechanical dimensions typically include a height of 18.35 mm, a width of 18.35 mm, and a depth of 89.6 mm, allowing them to fit comfortably into standard QSFP-DD sockets. The operating temperature range covers 0°C to 70°C, ensuring reliable performance in a variety of data center environments. With these mechanical specifications, Cisco's 400G QSFP-DD optical transceivers offer the perfect blend of compactness, versatility, and resiliency to effectively meet the mechanical requirements of modern data centers.

Types of QSFP-DD Transceivers


Cisco offers a range of 400G QSFP-DD optical transceivers to meet different applications and distance requirements. The following is a brief overview of the various types of transceivers:

400G QSFP-DD SR8 Optical Module

The 400G QSFP-DD SR8 transceiver is ideal for short-haul data center applications. It uses eight parallel multimode fiber channels, each running at 50G for a cumulative 400G. The SR100 has a transmission distance of up to 8m over OM4 fiber, making it an excellent choice for close data center interconnects.

400G QSFP-DD DR4 Optical Module

The 400G QSFP-DD DR4 transceiver is designed for medium-distance applications. It uses four parallel single-mode fiber channels, each running at 100G for a total of 400G. The DR4 can transmit data over distances of up to 500m, making it suitable for medium-haul data center interconnections.

400G QSFP-DD FR4 Optical Module

The 400G QSFP-DD FR4 transceiver is designed for long-haul applications. It uses four parallel single-mode fiber channels, each running at 100G, for 400G operation. With a maximum reach of 4 km, the FR2 is ideal for long-haul data center interconnects or campus networks.

400G QSFP-DD LR4 Optical Module

The 400G QSFP-DD LR4 transceiver is designed for ultra-long-haul applications. It utilizes four parallel single-mode fiber channels, each operating at 100G, which combine to achieve 400G operation. With data transmission distances of up to 4 km, the LR10 is ideal for connecting geographically diverse data centers.

Interoperability and Compatibility


Cisco 400G QSFP-DD optical transceivers are designed with interoperability in mind. They are interoperable with OSFP (Octal Small Form Factor Pluggable) transceivers, a similar standard for 400G transceivers. This allows for seamless integration and flexible network configuration, especially in mixed hardware environments. However, it is worth noting that while both QSFP-DD and OSFP support 400G data rates, they have different form factors and may require their own hardware or adapters for interconnection.


CFP8 is another form factor for 400G transceivers, and Cisco's 400G QSFP-DD optical transceivers are also interoperable with these transceivers. The QSFP-DD is interoperable with the CFP8 module to support multiple network setups and enhance scalability. Despite interoperability, QSFP-DD and CFP8 have different form factors and power profiles, so network designers should consider these factors when planning their network architectures.


Cisco's 400G QSFP-DD optical transceivers are backward compatible with existing QSFP transceivers. This ensures that network operators can incrementally upgrade their networks from 100G to 400G without having to overhaul their existing infrastructure. The QSFP-DD module features an additional row of contacts that allow it to handle four times the data rate of QSFPs, enabling a smooth transition to higher bandwidths while protecting existing investments.

Deployment Considerations

The following considerations should be kept in mind when deploying Cisco 400G QSFP-DD optical modules in the data center:

Optical Networking

Cisco 400G QSFP-DD optical transceivers are available for different visual network requirements and offer different variants for different distances and applications. Depending on the deployment environment, select the transceiver model that best fits your distance and bandwidth requirements. For example, a 400G QSFP-DD SR8 transceiver would be ideal for short distance data center-to-data center connectivity.

Data Center Deployment

Data centers often require high-performance, reliable, and energy-efficient networking equipment. Cisco's 400G QSFP-DD optical transceivers are ideal for such environments because of their low power consumption and high data rates. They are also interoperable with other transceiver standards, such as OSFP and CFP8, and backward compatible with QSFP transceivers, ensuring seamless integration into existing data center infrastructures.

Breakout and Aggregation

For use cases where traffic needs to be broken down into smaller streams, Cisco 400G QSFP-DD optical transceivers support breakout mode, where the data stream can be divided into multiple low-speed connections. Conversely, to aggregate numerous low-speed links into a single high-speed connection, these transceivers also support aggregation mode. This flexibility to handle different traffic patterns makes these transceivers an excellent choice for dynamic data center environments.

In summary, Cisco's 400G QSFP-DD optical transceivers are a strategic solution to meet the urgent need for increased bandwidth and efficiency in the data center. They offer a range of options to meet distance requirements from short- to ultra-long-haul applications. Interoperability with other standards, such as OSFP and CFP8, and backward compatibility with QSFP make them a versatile option for a variety of network architectures. The ability to support breakout and aggregation modes allows flexibility in managing different traffic patterns. Investing in 400G QSFP-DD optical transceivers is a forward-looking move that ensures immediate network performance enhancements and a future-proof infrastructure to meet growing data demands.

Frequently Asked Questions (FAQ)

Q: What is the purpose of the Cisco 400G QSFP-DD Optical Transceiver?

A: Cisco 400G QSFP-DD optical transceivers are designed to provide high-speed, high-density optical connectivity for data center applications.

Q: What does QSFP-DD stand for?

A: QSFP-DD stands for Quad Small Form Factor Pluggable Dual Density. It is an optical transceiver form factor that supports higher data rates and higher port densities than traditional QSFP transceivers.

Q: What types of optical transceivers are available in the Cisco 400G QSFP-DD series?

A: The Cisco 400G QSFP-DD Series includes multiple types of optical modules, such as FR4, DR4, LR4, SR8, and XDR4.

Q: What is the maximum distance supported by Cisco 400G QSFP-DD FR4 transceivers?

A: Cisco 400G QSFP-DD FR4 transceivers support a maximum distance of 2 kilometers of single-mode fiber (SMF).

Q: What is the difference between an active optical cable (AOC) and a branch cable?

A: Active optical cables (AOC) are complete optical modules with integrated transmitters and receivers designed for direct connections between switches, servers and storage devices. On the other hand, branch cables are used to split QSFP-DD ports into multiple duplex LC connectors.

Q: Can Cisco 400G QSFP-DD transceivers be used with previous generations of QSFP modules?

A: Cisco 400G QSFP-DD transceivers are backward compatible with QSFP and QSFP+ ports for seamless integration into existing optical networks.

Q: What is the form factor of the Cisco 400G QSFP-DD transceiver?

A: The Cisco 400G QSFP-DD transceivers have a compact form factor for high-density deployments in the data center.

Q: Are there any specific requirements for fiber optic cables when using Cisco 400G QSFP-DD transceivers?

A: The Cisco 400G QSFP-DD transceivers require single-mode fiber (SMF) cables for long-distance transmission. It is important to ensure that the correct type of cable is used for optimal performance.

Q: What is PAM4 modulation? Why is it critical for 400G Ethernet?

A: PAM4 (Pulse Amplitude Modulation Level 4) is a modulation scheme that allows for higher data rates and greater bandwidth efficiency than traditional NRZ (non-return-to-zero) coding. It is critical for 400G Ethernet because it enables the transmission of multiple bits per symbol to maximize the data capacity of the optical transceiver.

Q: What are the requirements for 400G Ethernet? Why?

A: The demand for 400G Ethernet is surging due to the increasing need for higher bandwidth and faster data transfer in data center environments. As more and more applications and services need to process and transmit large amounts of data, the demand for 400G Ethernet solutions continues to rise.