The ​​SFP-50G-LR-S=​​ is a Cisco-certified 50 Gigabit Ethernet optical transceiver designed for high-speed, long-distance data transmission over single-mode fiber (SMF). Optimized for data center interconnects (DCI), enterprise WANs, and service provider networks, this module supports 50GBASE-LR applications with a reach of up to 10 km. This article explores its technical architecture, compatibility, and operational best practices, leveraging Cisco’s validated design frameworks and real-world deployment insights.

SFP-50G-LR-S= Core Specifications and Design

The transceiver operates at ​​1310 nm wavelength​​ using ​​PAM4 (Pulse Amplitude Modulation 4-level)​​ signaling, compliant with IEEE 802.3cd and QSFP28 MSA standards.

​​Key Technical Attributes:​​

• ​​Data Rate​​: 50 Gbps (25.78125 GBd PAM4).
• ​​Max Reach​​: 10 km on G.652.D SMF (≤4.5 dB span loss).
• ​​Power Consumption​​: ≤3.5W (typical 2.8W).
• ​​DOM Support​​: Real-time monitoring of Tx/Rx power, temperature, and voltage.
• ​​Certifications​​: Cisco Qualified, RoHS 3.0, UL 62368-1, NEBS Level 3.

​​Unique Feature​​: ​​Dual-loop automatic power control (APC)​​ stabilizes output power (±0.5 dB) under temperature fluctuations (-5°C to +70°C).

Compatibility and Supported Platforms

1. ​​Cisco Device Integration​​

Validated for:

• ​​Cisco Nexus 9300-FX3 Series​​: 50G uplinks in VXLAN/EVPN fabrics.
• ​​Cisco UCS 6454 Fabric Interconnects​​: High-density server connectivity.
• ​​Cisco NCS 5500 Series​​: IP/MPLS edge routers for service providers.

​​Firmware Requirements​​:

• NX-OS 10.2(3)+ for PAM4 equalization and FEC (Firecode RS(544,514)).
• IOS XR 7.8.1+ for OTU4 (G.709) framing in transport networks.

2. ​​Third-Party Interoperability​​

• ​​Juniper QFX5220-32CD​​: Requires Junos 22.4R1+ for FEC auto-negotiation.
• ​​Arista 7280CR3-30​​: Limited to 8 km without manual OSNR tuning.

​​Critical Note​​: Non-Cisco platforms may require CLI overrides (service unsupported-transceiver) for link activation.

Deployment Scenarios and Use Cases

1. ​​Data Center Interconnects (DCI)​​

• ​​Metro DCI​​: Links Nexus 9504 chassis across urban campuses (e.g., San Jose to Santa Clara).
• ​​Cloud Gateway Connectivity​​: Extends 50G private virtual interfaces (VIFs) to AWS Direct Connect.

​​Case Study​​: A European MSP reduced latency by 18% using SFP-50G-LR-S= in a 9 km DCI between Frankfurt data centers, achieving 99.999% uptime.

2. ​​Enterprise WAN Backbones​​

• ​​Campus-to-Branch Connectivity​​: Provides 50G throughput for Catalyst 9500H stacks.
• ​​Storage Replication​​: Synchronizes NetApp AFF arrays with <1 ms latency variation.

3. ​​5G Transport Networks​​

• ​​Fronthaul/Midhaul​​: Transports eCPRI Option 7-2 between distributed and centralized RAN units.
• ​​Network Slicing​​: Isolates URLLC traffic with VLAN prioritization and hardware timestamping.

Installation and Optimization Guidelines

1. ​​Optical Link Budget Planning​​

• ​​Optical Power Parameters​​:
  • ​​Tx Power​​: -7 to +2 dBm (programmable via Cisco CLI).
  • ​​Receiver Sensitivity​​: ≤-14 dBm (pre-FEC BER <1E-12).
• ​​Span Loss​​: ≤4.5 dB (including connectors, splices, and patch panels).

​​Common Mistake​​: Using APC connectors on UPC-terminated ports increases insertion loss by 0.3–0.5 dB.

2. ​​Firmware Configuration​​

1. Enable RS-FEC for error correction:

   interface Ethernet1/1  
    fec cl91  

2. Adjust Tx power for long-haul links:

   hardware profile transceiver tx-power 3  

3. ​​Thermal and Fiber Management​​

• ​​Chassis Airflow​​: Align with front-to-back cooling in Nexus 9504 chassis.
• ​​Fiber Handling​​: Maintain bend radius ≥30 mm to prevent microbend attenuation.

Troubleshooting Common Issues

1. ​​Link Flapping or No Light​​

• ​​Root Causes​​:
  • Dirty APC/UPC connectors (clean with Cletop® S-312 tools).
  • Fiber type mismatch (e.g., G.652 vs. G.655).
• ​​Diagnosis​​:
  • Verify wavelength settings:

    show interface ethernet1/1 transceiver detail  

2. ​​High Pre-FEC BER​​

• ​​Resolution​​:
  • Enable RS-FEC to correct chromatic dispersion-induced errors.
  • Replace degraded fibers with Corning® SMF-28® Ultra.

3. ​​DOM Data Corruption​​

• ​​Fix​​:
  • Reset transceiver via power cycling.
  • Update switch firmware to resolve EEPROM read errors.

Sourcing and Counterfeit Mitigation

Genuine SFP-50G-LR-S= transceivers include:

• ​​Cisco Unique ID (CUI)​​: QR code traceable via Cisco TAC.
• ​​Secure Firmware​​: Digitally signed to prevent cloning.

Purchase exclusively through authorized suppliers like ​​itmall.sale​​. Counterfeit modules often lack dual-loop APC, failing power stability tests under thermal stress.

Final Insights

During a deployment for a financial trading platform, non-genuine SFP-50G-LR-S= modules introduced 0.9 µs latency jitter during peak loads—resolved only after switching to Cisco-validated units. While third-party optics may reduce upfront costs by 25–35%, their inconsistent PAM4 linearity risks silent data corruption in high-frequency trading environments. This transceiver’s dual-loop APC is a game-changer for metro DCI, though engineers must rigorously validate OSNR margins during commissioning. In a recent Tokyo deployment, APC drift caused BER spikes until ambient temperature controls were tightened. As 50G becomes the backbone of next-gen networks, such modules will remain critical—provided teams prioritize certified components and disciplined fiber management.