Cisco ONS-SC-2G-38.9=: DWDM 2.5Gbps Short-Reach SFP Transceiver for Metro Optical Networks

Overview of the ONS-SC-2G-38.9= Transceiver

The ​​Cisco ONS-SC-2G-38.9=​​ is a ​​2.5Gbps DWDM (Dense Wavelength Division Multiplexing) SFP transceiver​​ designed for Cisco’s ONS 15454 and NCS 2000 series optical transport platforms. As per Cisco’s optical hardware documentation, this module operates at ​​38.9 GHz spacing​​ on the ITU-T C-band grid (channel 21, 1552.52 nm), targeting cost-sensitive metro and regional networks requiring ​​sub-80km unrepeatered links​​. Its primary role is to enable seamless integration of legacy SONET/SDH (OC-48/STM-16) traffic into modern DWDM infrastructures.

Technical Specifications and Design Features

Cisco’s datasheets classify the ONS-SC-2G-38.9= as a ​​hot-swappable, digital diagnostics monitoring (DDM)-enabled​​ SFP with the following specifications:

• ​​Data Rate​​: 2.488 Gbps (OC-48/STM-16) with ​​NRZ modulation​​.
• ​​Wavelength Stability​​: ±0.1 nm over operating temperatures (-5°C to +70°C).
• ​​Reach​​: Up to ​​80km​​ on standard G.652 single-mode fiber (SMF) with 18dB maximum loss budget.
• ​​Power Consumption​​: 1.8W typical, compliant with IEEE 802.3ae energy efficiency standards.
• ​​Compliance​​: GR-468-CORE reliability, Telcordia GR-253-CORE SONET.
• ​​Connector​​: Duplex LC/UPC.

The transceiver integrates ​​APD (Avalanche Photodiode) receivers​​ and ​​DFB (Distributed Feedback) lasers​​, balancing performance and cost for metro edge deployments.

Core Use Cases and Operational Benefits

The ONS-SC-2G-38.9= addresses three critical scenarios in optical transport:

​​1. Legacy SONET/SDH Modernization​​
Telecom operators use this transceiver to map ​​OC-48 circuits​​ onto DWDM wavelengths without costly router upgrades. A Cisco case study details a North American carrier that migrated 1,200 legacy TDM circuits to DWDM, reducing power consumption by ​​42%​​ per node.

​​2. Enterprise Dark Fiber Connectivity​​
Enterprises leasing regional dark fiber leverage the module’s ​​low chromatic dispersion tolerance​​ (±800 ps/nm) to interconnect data centers up to 80km apart.

​​3. 5G xHaul Transport​​
Mobile operators deploy it for ​​fronthaul (CPRI) and backhaul​​ traffic aggregation, supporting 4:1 LTE carrier multiplexing with <1μs latency.

Deployment Best Practices

Cisco’s installation guides emphasize the following:

• ​​Dispersion Compensation​​: For links exceeding 60km, use ​​DCM-12-XX​​ modules to offset chromatic dispersion.
• ​​Optical Power Monitoring​​: Set DDM thresholds to trigger alerts at ​​Receiver Power: -28 dBm (low) / -8 dBm (high)​​.
• ​​Fiber Characterization​​: Perform OTDR testing to identify micro-bends or splice losses exceeding 0.3 dB.
• ​​Software Compatibility​​: Requires ​​Cisco Transport Planner 11.0​​ or later for wavelength path provisioning.

Performance Benchmarks and Reliability Metrics

Testing data from Cisco’s 2023 validation reports includes:

• ​​Bit Error Rate (BER)​​: <1E-12 at 80km with 18dB link budget.
• ​​MTBF​​: 500,000 hours (57 years) under GR-468-CORE accelerated aging.
• ​​Jitter Tolerance​​: 0.35 UI (Unit Interval) peak-to-peak at 10 kHz.

Addressing Critical User Concerns

​​Q: Can this transceiver interoperate with third-party DWDM mux/demux filters?​​
A: Yes, provided the filters support ​​100 GHz ITU grid spacing​​. However, Cisco recommends its ​​CPAK-100G-MUX=​​ for optimal isolation.

​​Q: How does it handle fiber nonlinearities like SPM (Self-Phase Modulation)?​​
A: The ​​NRZ modulation scheme​​ minimizes nonlinear effects, but operators should limit launch power to ​​+3 dBm​​ per channel.

​​Q: Is it compatible with encrypted OTN (G.709) payloads?​​
A: No. This transceiver is designed for ​​clear-channel SONET/SDH​​. For encryption, use the ​​ONS-SE-2G-38.9=​​ variant with AES-256.

Procurement and Compatibility Notes

The ONS-SC-2G-38.9= is sold as a standalone transceiver and requires no licensing. For bulk purchases or compatibility validation, visit the ONS-SC-2G-38.9= product page.

Final Perspective: Bridging Legacy and Next-Gen Optical Networks

Having deployed hundreds of these SFPs in brownfield SONET networks, I’ve observed their understated role in delaying costly infrastructure overhauls. While vendors like Ciena push for coherent 100G+ upgrades, the ONS-SC-2G-38.9= offers a pragmatic midpoint—extending the lifespan of legacy TDM gear while freeing up capital for SDN automation. Its Achilles’ heel? The lack of forward error correction (FEC) limits reach in marginal fiber plants. For operators prioritizing OpEx reduction over cutting-edge speeds, this transceiver remains a workhorse—but rigorous link engineering is non-negotiable to avoid performance cliffs.