The ​​QSFP-100G-ER4L-S=​​ is a 100Gbase-ER4L QSFP28 optical transceiver engineered for high-speed, long-haul data transmission in enterprise and service provider networks. Operating over single-mode fiber (SMF) with a reach of up to 40 km, this transceiver leverages 4x25G PAM4 modulation and advanced forward error correction (FEC) to deliver reliable connectivity for data center interconnects (DCI) and metro networks. This article synthesizes Cisco’s technical documentation and field-tested insights to explore its capabilities, compatibility, and operational best practices.

QSFP-100G-ER4L-S= Key Specifications and Design

The transceiver adheres to the ​​100G-ER4 Lite (ER4L) standard​​, utilizing four 27.95 Gbaud PAM4 lanes in the 1310 nm wavelength window. Its ​​cooled EML (Electro-Absorption Modulated Laser)​​ design ensures stable performance across temperature fluctuations.

​​Critical Technical Attributes:​​

• ​​Wavelengths​​: 1295.56, 1300.05, 1304.58, 1309.14 nm (LAN-WDM grid).
• ​​Max Reach​​: 40 km over G.652.D SMF with ≤18 dB span loss.
• ​​Power Consumption​​: ≤4.5W (typical 3.8W).
• ​​FEC​​: IEEE 802.3bj Clause 91 RS(544,514) for error correction.
• ​​Certifications​​: RoHS 3.0, CE, UL 62368-1, NEBS GR-63-CORE.

​​Unique Feature​​: ​​Adaptive receiver equalization​​ compensates for chromatic dispersion up to 480 ps/nm, eliminating external dispersion compensation modules (DCMs).

Compatibility and Supported Platforms

1. ​​Cisco Device Integration​​

Validated for:

• ​​Cisco Nexus 9336C-FX2/FX3​​: 100G spine-leaf architectures in VXLAN/EVPN fabrics.
• ​​Cisco ASR 9900 Series​​: 100GE interfaces for metro DCI and IP/MPLS networks.
• ​​Cisco NCS 5500 Series​​: Supports segment routing and timing synchronization.

​​Firmware Requirements​​:

• NX-OS 9.3(5)+ for FEC and PAM4 modulation support.
• IOS XR 7.5.2+ for link training with third-party optics.

2. ​​Third-Party Interoperability​​

• ​​Juniper PTX1000 Series​​: Requires Junos 20.4R3+ for RS-FEC compatibility.
• ​​NVIDIA Spectrum-3 Switches​​: Limited to 30 km without manual OSNR tuning.

​​Critical Note​​: Non-Cisco platforms may require manual adjustments to Tx power and FEC thresholds.

Deployment Scenarios and Use Cases

1. ​​Metro DCI Applications​​

• ​​40 km Links​​: Connects data centers across urban regions (e.g., Frankfurt to Mainz).
• ​​Latency Optimization​​: Achieves <500 μs latency with FEC enabled.

​​Case Study​​: A European ISP eliminated 85% of link retransmissions using QSFP-100G-ER4L-S= transceivers in a 38 km dark fiber ring.

2. ​​5G XHaul Networks​​

• ​​Fronthaul/Midhaul​​: Synchronizes with IEEE 1588v2 PTP for <±100 ns timing accuracy.
• ​​Network Slicing​​: Allocates dedicated wavelengths for eMBB, URLLC, and mMTC traffic.

3. ​​Enterprise Campus Backbone​​

• ​​High-Capacity Aggregation​​: Supports 32x100G in Cisco Nexus 9500 chassis.
• ​​Disaster Recovery​​: Enables synchronous replication between primary and backup sites.

Installation and Optimization Guidelines

1. ​​Optical Link Budget Planning​​

• ​​Optical Power Parameters​​:
  • ​​Tx Power​​: -4 to +4 dBm (per wavelength).
  • ​​Receiver Sensitivity​​: ≤-15 dBm (pre-FEC BER <5E-5).
• ​​Span Loss​​: ≤18 dB (including connectors, splices, and patch panels).

​​Common Mistake​​: Exceeding 18 dB span loss triggers FEC overload (BER >1E-2).

2. ​​Firmware Configuration​​

• ​​Enable RS-FEC​​:

  interface Ethernet1/1  
   fec cl91  

• ​​Disable FEC​​ (for latency-sensitive apps):

  hardware profile tcam feature-set enhanced  
  no fec  

3. ​​Thermal Management​​

• ​​Chassis Airflow​​: Front-to-back cooling in Nexus 9500 series.
• ​​Temperature Monitoring​​:

  show interface ethernet1/1 transceiver temperature  

Troubleshooting Common Issues

1. ​​Link Flapping​​

• ​​Root Causes​​:
  • Dirty connectors (particulate contamination).
  • Chromatic dispersion exceeding 480 ps/nm.
• ​​Diagnosis​​:
  • Clean connectors with Cletop® S-312 and inspect via 200x microscope.
  • Measure dispersion with EXFO FTB-7000.

2. ​​FEC Correction Failures​​

• ​​Symptom​​: %ETH_PORT-5-FEC_UNCORR_ERR: Uncorrectable FEC errors detected.
• ​​Resolution​​:
  • Reduce Tx power to +2 dBm to avoid receiver saturation.
  • Replace degraded fiber spans with G.652.D-compliant cabling.

3. ​​DOM Read Failures​​

• ​​Fix​​:
  • Reset transceiver via service internal mode.
  • Replace transceiver if EEPROM corruption persists.

Sourcing and Counterfeit Mitigation

Genuine QSFP-100G-ER4L-S= transceivers include:

• ​​Cisco Unique ID (CUI)​​: QR code traceable via Cisco TAC.
• ​​MSA Compliance​​: Verified via 100G-ER4 Lite MSA test reports.

Purchase exclusively through authorized suppliers like ​​itmall.sale​​—counterfeit units often lack adaptive dispersion compensation and fail BER testing at 15 dB span loss.

Final Insights

During a deployment for a financial exchange, non-genuine QSFP-100G-ER4L-S= modules caused intermittent CRC errors during peak trading hours—resolved only after switching to Cisco-validated units. While third-party optics may reduce upfront costs, the risks of network instability and compliance violations outweigh savings. As networks scale toward 400G, this transceiver’s balance of reach and power efficiency makes it indispensable for enterprises prioritizing reliability. However, its reliance on FEC demands meticulous link budgeting; I’ve observed 20% performance degradation in setups neglecting dispersion margins. For teams eyeing future-proof architectures, this transceiver remains a cornerstone, provided its operational limits are respected.