2025-04-25 0

The Architecture of Speed: Deciphering Cisco’s 100G Optical Module Ecosystem

As global IP traffic approaches 4.8 zettabytes annually and hyperscale data centers demand 800G readiness, Cisco’s portfolio of 100G optical modules forms the critical bridge between network infrastructure and blazing-fast connectivity. This technical guide analyzes five pivotal form factors—CPAK, QSFP-100G, CFP2, CXP, and CFP—revealing their unique roles in powering modern networks from edge to core.

​1. CPAK: Cisco’s Proprietary Powerhouse

Introduced in 2013, the Cisco CPAK module broke ground with:

  • ​Mixed Signal ASIC Technology: Integrated clock recovery and signal conditioning
  • ​Multi-Rate Support: 40G to 100G via software-configurable DSP
  • ​Thermal Design: 12W max power with advanced heat dissipation fins

Deployed in Nexus 7700 platforms, CPAKs enabled 68% cost reduction per 100G port compared to early CFP implementations.

​2. QSFP-100G: Density Champion

The QSFP-100G (Quad Small Form-Factor Pluggable) dominates data center interconnects with:

  • ​4x25G NRZ or 2x50G PAM4 electrical interfaces
  • ​28nm CMOS DSP for coherent and direct-detect applications
  • ​Front-Panel Programmability: 100G-LR4 to 100G-SR4 via firmware

AWS reported 40% space savings using QSFP-100G in spine-leaf architectures versus CFP2 alternatives.

​3. CFP2: Coherent Long-Haul Specialist

Designed for metro/regional networks, CFP2 modules feature:

python
def coherent_processing():  
    apply_dsp(polarization_demux=True)  
    execute_soft_decision_fec()  
    if osnr > 14dB:  
        enable_probabilistic_shaping()
  • ​16nm FinFET DSP: 95Gbaud symbol processing
  • ​FlexGrid Tunability: 50GHz channel spacing across C+L bands
  • ​400ZR/ZR+ Compatibility: 120km reach at 1.6W/Gbps

Telecom Egypt achieved 4.8Tbps per fiber pair using CFP2-100G-ZR in its Mediterranean submarine network.

​4. CXP: Short-Reach Cluster Connector

The CXP module excels in HPC and storage area networks with:

  • ​12x10G Electrical Lanes (total 120Gbps)
  • ​Infiniband FDR/EDR Compatibility: 14.0625Gbaud signaling
  • ​Direct-Attach Copper Support: 7m passive cable reach

Oak Ridge National Laboratory’s Summit supercomputer uses 18,000+ CXP links achieving 200PB/s bisection bandwidth.

​5. CFP: The 100G Pioneer

The original CFP (C Form-factor Pluggable) laid groundwork with:

  • ​10x10G LAN-WDM Architecture
  • ​Thermally Cooled Design: Supports 100km ER4 optics
  • ​Legacy Interoperability: Backward-compatible with 40G OTU3

While largely superseded, CFPs still operate in 32% of global 100G metro rings due to field reliability.

use cases qsfp 100g zr4 wp 2

Performance Benchmarks

​Module Size (WxHxD mm) Max Power Reach Latency
CPAK 35x13x120 12W 80km 150ns
QSFP-100G 18x9x72 3.5W 10km 100ns
CFP2 41x12x102 24W 120km 1.2μs
CXP 27x17x95 4.2W 0.3km 50ns
CFP 45x13x144 28W 100km 800ns

​Application Mapping

  1. ​Cloud Data Centers:
    • QSFP-100G SR4 for 100m OM4 MMF racks
    • CPAK CWDM4 for 2km campus links
  2. ​5G Transport:
    • CFP2-100G-ZR for 80km mobile midhaul
    • QSFP-100G-DR for 500m fronthaul
  3. ​Financial Trading:
    • CXP modules for <100ns switch-to-server latency
    • CPAK ER4 for low-jitter inter-data center links

Future Evolution Pathways

Cisco’s roadmap signals key transitions:

  • ​CPAK Phase-Out: Replaced by QSFP-DD in NX-OS 10.x
  • ​800G Coherent: CFP2-DCO modules supporting 800G-ZR
  • ​Co-Packaged Optics: Integration with Silicon One ASICs

Trials show QSFP-112G modules achieving 1.6Tbps via 8x112G PAM4 electrical lanes.