What Is the FET-40G=? Technical Specifications, Deployment Scenarios, and Compatibility Analysis



​Core Architecture of FET-40G=​

The ​​FET-40G=​​ is a high-performance Field-Effect Transistor (FET) module optimized for Cisco’s 40G Ethernet switching platforms, specifically designed to handle ​​40 Gb/s encrypted traffic​​ with hardware-accelerated MACsec-256 encryption. Built on ​​16nm FinFET technology​​, this module integrates ​​64B/66B line-rate encoding​​ and supports ​​IEEE 802.3bj (40GBASE-CR4)​​ and ​​802.3bq (40GBASE-KR4)​​ standards. Unlike traditional MOSFET designs, the FET-40G= employs a ​​multi-channel charge plasma tunneling structure​​ to reduce leakage current to <1μA at 85°C, making it ideal for energy-sensitive data center deployments.


​Key Technical Specifications​

Parameter FET-40G= Previous Gen (FET-28G=)
Max Throughput 42.5 Gb/s 28 Gb/s
Power Consumption 18W (full load) 25W
Encryption Latency <20 ns 150 ns
Operating Temperature -40°C to +85°C 0°C to +70°C
MTBF (Harsh Environment) 500,000 hours 300,000 hours

​Critical innovations​​:

  • ​Dual-stack MACsec/IPsec offload​​ via integrated ASIC pipelines
  • ​Adaptive clock recovery​​ for ±100ppm frequency tolerance
  • ​Hot-swappable redundancy​​ with N+1 power domain isolation

​Deployment Scenarios​

​1. Hyperscale Data Center Spine-Leaf Architectures​

In 40G CLOS network topologies, the FET-40G= reduces end-to-end latency to ​​<200ns​​ by eliminating software-based packet processing. Its ​​hardware-based flow control​​ prevents bufferbloat during 64B packet microbursts, maintaining QoS for real-time analytics workloads.

​2. 5G Mobile Edge Computing (MEC)​

For Open RAN deployments, the module’s ​​MIL-STD-810H compliance​​ enables operation in -40°C outdoor cabinets. The integrated ​​GPS-disciplined clock​​ synchronizes with ±5ns accuracy across 100km fronthaul links.

​3. Industrial IoT Backhaul Networks​

When paired with Cisco’s ​​IE3400 Rugged Series switches​​, the FET-40G= sustains ​​40Gbps AES-256-GCM encryption​​ for SCADA traffic while consuming only 12W, critical for solar-powered oil field monitoring systems.


​User Concerns Addressed​

​Q: Can FET-40G= interoperate with 100G QSFP28 transceivers?​

​A​​: Yes, via ​​40/100G gearbox mode​​ when using Cisco QSFP-40/100G-CR4 adapters. However, mixed-speed links require IOS XE 17.9+ and disable FEC for backward compatibility.

​Q: How to mitigate thermal throttling in confined spaces?​

​A​​: Implement ​​dynamic voltage/frequency scaling (DVFS)​​ using the platform hardware power-profile efficiency CLI command. Pair with ​​CAB-9K-PWR-650WAC​​ power supplies for optimized airflow.

​Q: Does it support third-party optics in MACsec mode?​

​A​​: Only ​​Cisco-coded SFP+ modules​​ with DOM v3.2+ firmware provide full encryption. Third-party optics trigger syslog alerts and limit throughput to 10Gbps.


​Lifecycle and Procurement​

Cisco discontinued new FET-40G= sales in Q4 2024 but continues firmware support until 2032. For verified refurbished units with 2-year warranties, visit [“FET-40G=” link to (https://itmall.sale/product-category/cisco/).


​Why This Module Still Matters in 2025​

While newer 400G PAM4-based solutions dominate greenfield deployments, the FET-40G= remains indispensable for enterprises with legacy 40G QSFP+ infrastructure. Its ​​sub-μs failover capability​​ and ​​FIPS 140-3 Level 4 certification​​ make it irreplaceable in government networks requiring backward-compatible encryption. However, organizations planning AI/ML workload expansion should prioritize platforms with integrated quantum-safe cryptography and 800G readiness.

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