Cisco QDD-400G-LR4-S 400G QSFP-DD Transceiver

Cisco QDD-400G-LR4-S QSFP-DD 400G Transceiver

The Cisco QDD-400G-LR4-S is a high-density QSFP-DD transceiver engineered for ultra-high-speed optical links. Delivering 400 Gbps over single-mode fiber with duplex LC connectors, this module implements the 400GBASE-LR4 standard to support long-reach backbone and data center interconnects up to 10 kilometres. Optimized for demanding campus, metro and hyperscale environments, it pairs Cisco reliability with industry-standard connectivity.

Key specifications

• Manufacturer: Cisco
• Part number / SKU: QDD-400G-LR4-S
• Product type: Optical transceiver module
• Sub-type / Speed: 400 Gbps (400 GBPS)
• Form factor: QSFP-DD (Quad Small Form-factor Pluggable — Double Density)
• Cabling: Single-mode fiber (SMF)
• Connector: Duplex LC
• Optical lanes / Wavelengths: LR4 coarse wavelength division — 1270 nm, 1290 nm, 1310 nm, 1330 nm
• Maximum reach: 10 km
• Supported protocol: Gigabit Ethernet (compatible with 400GBASE-LR4)

Technical overview

Built to meet large-scale network throughput demands, the QDD-400G-LR4-S uses four DWDM-like wavelengths multiplexed over a single SMF pair. Its QSFP-DD form provides double-density port counts on switches and routers compared with QSFP28, enabling more bandwidth per rack unit while maintaining Cisco's strict manufacturing and interoperability standards.

Optical & electrical characteristics

• Four optical lanes combined into a single 400G link using LR4 wavelength assignment.
• Duplex LC interface for straightforward integration with existing single-mode fiber infrastructure.
• Designed to meet industry optical budgets for 10 km links without inline amplification.
• Compliant with relevant IEEE and MSA specifications for 400G QSFP-DD modules.

Performance highlights

• High throughput: native 400 Gbps data-plane capacity for north-south and east-west traffic aggregation.
• Extended reach: supports up to 10 km on standard single-mode fiber, ideal for campus-to-campus or metro interconnects.
• Energy-efficient operation compared with multiple lower-speed modules delivering the same aggregate bandwidth.

Use cases and deployments

The QDD-400G-LR4-S excels wherever large-capacity, low-latency optical channels are required. Typical deployments include:

• Hyperscale data center spine and fabric links where port density and power-per-bit are critical.
• Carrier and metro aggregation rings linking POPs across short metro distances (within the 10 km budget).
• Enterprise campus backbones connecting dispersed buildings or remote data rooms over single-mode fiber.
• High-performance computing clusters and storage interconnects demanding consistent 400G throughput.

Compatibility & standards

• Form-factor: QSFP-DD compliant host platforms from Cisco and other vendors that accept QSFP-DD optics.
• Data protocol: Operates with Ethernet at high-speed variants including 400GBASE-LR4.
• Optical standards: LR4 wavelength plan (1270 / 1290 / 1310 / 1330 nm) for four-lane LR operation over SMF.
• Interoperability: Engineered to meet Cisco transceiver compatibility requirements — verify platform compatibility matrix before purchase.

Cisco QDD-400G-LR4-S QSFP-DD Transceiver

The Cisco QDD-400G-LR4-S is a high-density, pluggable optical transceiver engineered for the most demanding metro, campus and data center interconnect (DCI) applications. Built to the QSFP-DD form factor, this module provides a standard-compliant 400GBASE-LR4 single-mode fiber link over duplex LC connectors for distances up to 10 km on standard single-mode fiber (SMF). It is designed to deliver ultra-high throughput with power efficiency and physical density that modern networks require.

Key features and benefits

High-capacity 400G performance

The QDD-400G-LR4-S supports native 400 Gigabit Ethernet throughput, enabling network operators to collapse multiple 100G/200G links and simplify topologies. This reduces the number of required ports and optical fibers while increasing per-port capacity.

QSFP-DD form factor — density and backward compatibility

QSFP-DD (Quad Small Form-factor Pluggable Double Density) doubles the lane count while maintaining backwards compatibility with QSFP28 and QSFP56 hosts (with appropriate support), allowing operators to mix-and-match modules during transitions to higher speeds. The compact QSFP-DD package maximizes port density in switches and routers.

Duplex LC connectors for single-mode fiber

Standard duplex LC connections simplify cabling and work with existing single-mode fiber infrastructures. The LR4 wavelength division multiplexing approach transmits four optical carriers over a single fiber pair, enabling 400G over 10 km without complex external optics.

Low power and thermal efficiency

Optimized electro-optical design helps lower power consumption per bit, reducing cooling loads and operating expenses in dense rack-mounted network equipment.

Standards compliance and carrier-grade reliability

• Compliant with IEEE and industry pluggable module standards for 400GBASE-LR4.
• Manufactured to Cisco’s quality and interoperability requirements for use in Cisco networking equipment.
• Includes diagnostics and digital monitoring functions (DMI/DOM) for real-time module health and performance data.

Electrical and management

• Host interface: 8-lane electrical interface supporting 400G operation.
• Power consumption: Optimized for low power per bit (refer to datasheet for exact values per part number and firmware revision).
• Management: SFF-8636/SFF-8679 style control and diagnostic monitoring (I²C/MDIO accessible DOM/DMI).

Environmental and compliance

• Temperature range: Designed for data center ambient rating (consult datasheet for industrial options).
• RoHS and WEEE compliant.
• Electrostatic discharge (ESD) protection and safety certifications as per Cisco QA standards.

Use cases and deployment scenarios

Data center spine-leaf aggregation

In modern spine-leaf architectures, 400G uplinks provide the necessary east-west bandwidth to support heavy east-west traffic patterns created by virtualization, containerization and distributed applications. The QDD-400G-LR4-S is ideal as a spine uplink or leaf aggregation link where 10 km reach is required between buildings or across campus fiber rings.

Data center interconnect (DCI)

For linking adjacent data center facilities or co-located sites over metro single-mode fiber, 400GBASE-LR4 balances cost and reach. It offers more economical fiber usage than parallel-fiber solutions while remaining compatible with standard duplex LC cabling.

Carrier aggregation and edge routing

Service providers delivering high-bandwidth services (e.g., 5G backhaul, cloud on-ramps) can leverage 400G links to consolidate multiple lower-speed circuits into a single, manageable pipe with lower port count and improved spectral efficiency.

Campus backbone upgrades

Enterprises modernizing campus backbones to support AI/ML workloads, high-resolution video and large file transfers will find 400G an efficient upgrade path—particularly where existing single-mode fiber between buildings spans distances up to 10 km.

Compatibility and interoperability

Supported Cisco platforms

The QDD-400G-LR4-S is designed to interoperate with a range of Cisco fixed and modular switches, routers and optical platforms that include QSFP-DD ports and firmware support for 400GBASE-LR4 optics. Always verify platform firmware and supported optics lists before deployment to ensure full feature compatibility (DMI, auto-negotiation, link training where applicable).

Backward compatibility and migration paths

• QSFP-DD hosts may accept lower-speed QSFP modules through adapters or supported mode settings, enabling phased migration from 100G/200G to 400G.
• Network designers often use a mix of 100G/200G and 400G ports during upgrades; careful planning of optical patching and link aggregation strategies reduces disruption.

Performance considerations

Optical budget and reach

400GBASE-LR4 uses four wavelengths combined over a duplex fiber pair. While the nominal reach is up to 10 km on standard SMF, real-world reach depends on fiber attenuation, connector loss, splice counts and margin for aging. Plan optical budgets conservatively and run link tests (OTDR, power meter) during installation.

Latency and jitter

Pluggable optics add negligible latency at the scale of microseconds and are generally not the limiting factor for latency-sensitive applications; network design (switching, queuing) will have a larger impact. 400G links can actually reduce end-to-end latency by collapsing multiple hops into a single high-capacity pipe.

Forward error correction (FEC) and link reliability

Many 400G deployments leverage FEC to improve error rates and extend practical reach. Verify whether your host platform enforces FEC for LR4 links and ensure both ends are configured consistently to avoid link negotiation problems.

Comparison with alternative 400G options

400GBASE-SR8 (parallel multimode) vs 400GBASE-LR4

SR8 uses parallel multimode fiber with an MPO/MTP connector and is optimized for short-reach (up to ~100 m) within the same data center EDA. LR4, by contrast, uses duplex LC SMF and reaches up to 10 km—making it preferable for inter-room, inter-building and metro connections.

400GBASE-FR4 / CWDM-based alternatives

Other 400G single-mode options may use different wavelength multiplexing schemes or line coding to achieve intermediate reaches. LR4 is a proven, standardized choice when 10 km reach with duplex LC cabling is the requirement.

Order options, lifecycle and part numbering

Part number explanation

The Cisco part number QDD-400G-LR4-S indicates a QSFP-DD (QDD) 400G LR4 module for single-mode duplex LC (LR4-S). Variants for extended temperature ranges, vendor-branded firmware, or different qualification levels may exist—check Cisco’s product matrix and the platform’s compatibility list when purchasing.

Supply chain and lifecycle

Optical modules may have multiple product lifecycle stages: Available, End-of-Sale, End-of-Life. For critical builds, procure spares and check for official replacement parts if the part moves to legacy status. Cisco typically publishes product lifecycle notices and replacement guidance for end-of-sale optics.

Security, compliance and environmental considerations

Operational security

Pluggable optics do not inherently introduce network security risks beyond physical access concerns. Enforce physical control of equipment rooms and restrict port access with configuration best practices at the switch/router level to prevent unauthorized use.

Regulatory compliance

Cisco transceivers are typically designed to meet regional safety and electromagnetic compatibility (EMC) regulations (e.g., CE, FCC) as well as environmental standards (RoHS). Confirm compliance declarations if deploying in regulated environments or for public sector projects.

Sustainability and disposal

At end of life, optics should be recycled per local electronic waste regulations. Cisco provides guidance on product recycling; follow organizational sustainability policies to minimize environmental impact.