Arista QDD-800G-2VSR4 Compatible LINK-PP 800GBASE-SR8 QSFP-DD 850nm 50m Dual MPO-12/APC DOM MMF Transceiver Module

Product Specifications

Arista QDD-800G-2VSR4 Compatible LINK-PP LQD-DM85800-SR8C 800GBASE-SR8 QSFP-DD Optical Transceiver 850nm 50m Dual MTP/MPO-12 APC for Arista AI/ML Networks

The LINK-PP LQD-DM85800-SR8C is a high-performance, Arista QDD-800G-2VSR4 compatible 800G QSFP-DD optical transceiver engineered specifically for next-generation AI/ML backend fabrics, High-Performance Computing (HPC) clusters, and hyperscale data center core networks. Operating over multi-mode fiber (MMF), this uniquely designed hot-pluggable module utilizes a Dual MTP/MPO-12 APC interface, providing unparalleled cabling flexibility for high-density 2x 400G breakout architectures directly from Arista routing platforms.

Integrating eight parallel transmission and receiving lanes utilizing 100G PAM4 (Pulse Amplitude Modulation 4-level) electrical and optical signaling, the module achieves an aggregate data rate of 850Gbps (8x 106.25Gbps). Fully compliant with IEEE 802.3df, IEEE 802.3ck, QSFP-DD HW Rev 6.2, and CMIS 4.0 standards, it ensures pristine signal integrity up to 50m on OM4 fiber. By leveraging the Arista "2VSR4" (2x Virtual SR4) architecture alongside the Dual MPO-12 form factor, data center architects can seamlessly scale to 800G Ethernet without requiring a massive overhaul of their existing Base-8 structured cabling infrastructure.

Application Topologies and Deployment Scenarios

The shift to 800G Ethernet is driven by the massive I/O demands of generative AI and deep learning workloads. The Dual MPO-12 design of this QSFP-DD module solves one of the most significant physical layer challenges in hyperscale Arista environments: legacy fiber compatibility and breakout routing.

Native 2x 400GBASE-SR4 Breakout Architecture (The "2VSR4" Advantage)

The primary architectural advantage of the Arista QDD-800G-2VSR4 design is native, hardware-level fractionalization. Instead of using expensive, custom MPO-16 to 2x MPO-12 conversion cables, network engineers can plug two standard MPO-12 cables directly into the front of this single 800G transceiver. This allows an 800G switch port (such as those on Arista 7060X5 or 7800R3 Series) to operate as two independent 400G ports connecting directly to legacy 400GBASE-SR4 spine switches or 400G NICs, maximizing switch silicon utilization.

Reusing Base-8 Data Center Infrastructure

Many modern data centers are built on Base-8 MPO structured cabling (utilizing 8 fibers out of a 12-fiber MPO connector for 40G/200G/400G SR4). Deploying standard 800GBASE-SR8 optics typically requires tearing out this infrastructure to install MPO-16 trunks. This dual-receptacle module allows operators to achieve 800G point-to-point links by simply aggregating two existing MPO-12 trunk cables, dramatically reducing upgrade CAPEX and installation time.

AI/ML GPU Cluster Fabrics

In large-scale AI training clusters, compute nodes require non-blocking, microsecond-latency interconnects. This module is an ideal deployment choice for bridging GPU-accelerated servers directly to Top-of-Rack (ToR) switches, forming a lossless Ethernet backend fabric capable of handling massive East-West RDMA (RoCEv2) traffic flows across high-throughput Arista EOS fabrics.

Physical Layer Design and Optical Performance Optimization

Transmitting 100Gbps per lane over multi-mode fiber pushes the physical limits of optical technology. LINK-PP transceivers integrate state-of-the-art optical engines and DSP (Digital Signal Processing) to ensure a zero-packet-loss physical layer.

8x 100G PAM4 VCSEL Array Architecture

Unlike legacy NRZ signaling, PAM4 transmits two bits per symbol via four distinct voltage/optical power levels. The transmission core utilizes an advanced 850nm VCSEL array optimized for 106.25Gbps baud rates. This requires extraordinary linearity and exceptionally low Relative Intensity Noise (RIN). The receiving end utilizes a matched high-bandwidth PIN array to accurately decode the complex PAM4 optical eye diagram.

The Dual MTP/MPO-12 APC Connector Interface

To support 8 TX and 8 RX lanes, this transceiver features two separate optical receptacles. More importantly, to handle the extreme sensitivity of 100G PAM4 signals to optical return loss (reflection), this multi-mode transceiver utilizes APC (Angled Physical Contact) interfaces. The 8-degree polish ensures that any reflected light is directed into the fiber cladding rather than bouncing back into the VCSEL laser cavity, preserving signal integrity.

Advanced Thermal Management

800G transceivers draw significantly higher power than legacy modules. This unit is engineered within a standard QSFP-DD housing featuring premium die-cast thermal pads. It dissipates heat efficiently away from the DSP and optical sub-assemblies, ensuring stable commercial operation (0°C to 70°C) without forcing Arista switch chassis fans into thermal runaway.

Multi-Vendor Compatibility and CMIS 4.0 Diagnostics

Managing an 800G fabric requires advanced software interfaces. This transceiver supports the Common Management Interface Specification to provide unprecedented visibility into the link state.

Arista EOS Compatibility and Hardware Validation

Engineered for seamless integration, the LQD-DM85800-SR8C undergoes rigorous EEPROM coding and hardware validation. It is natively recognized by Arista EOS (Extensible Operating System) as the QDD-800G-2VSR4 module. It guarantees plug-and-play interoperability in Arista 800G switching platforms, avoiding proprietary vendor lock-outs and syslog warnings.

CMIS Rev 4.0 Management Interface

Moving far beyond legacy SFF-8472 DOM, this module is fully compliant with CMIS 4.0. This advanced interface provides a robust state machine for module initialization, allowing the host Arista switch to manage firmware upgrades, configure datapath parameters, and negotiate power classes before enabling the VCSEL lasers.

Per-Lane Real-Time Telemetry

Network engineers can actively monitor the health of all 16 parallel channels (8 TX / 8 RX) via Arista CLI. Telemetry includes independent TX Bias Current, TX Optical Power, and RX Optical Power for every individual lane. This granular visibility is absolutely critical in AI fabrics, where a single degraded optical lane can throttle an entire GPU training cluster.

Selection Guide and Deployment Considerations

Deploying 800G PAM4 optics introduces strict new cabling rules that differ vastly from legacy networks. Follow these critical guidelines to prevent hardware damage and link failures.

The MPO-12 APC Cabling Requirement (Crucial Trap)

This is the most common deployment mistake in 800G multi-mode networks. Legacy MMF MPO-12 cables (like those used for 100G SR4 or 400G SR8) are typically PC/UPC (flat-polished). You MUST use MTP/MPO-12 APC (Angled) cables for this 800G transceiver. Forcing a standard flat UPC MTP cable into this module will physically crush the internal lens array and permanently destroy the transceiver.

Mandatory Host-Side FEC (Forward Error Correction)

PAM4 modulation at 106.25Gbps per lane inherently produces bit errors before correction. The 50m reach of this transceiver is strictly dependent on KP4 FEC (Clause 91 / Clause 119) being enabled on the host Arista switch port. Operating this module without host-side FEC is not supported and will result in massive packet loss and link failure.

Choosing Between Dual MPO-12 and MPO-16

• Dual MPO-12 (This Module): Ideal if your primary goal is connecting to two independent 400G switches (the "2VSR4" use case), or if you already have Base-8 / Base-12 MPO cabling installed in your data center.
• Single MPO-16: Ideal for native 800G point-to-point connections where you are pulling brand new fiber trunks and want to minimize cable bulk at the switch faceplate.