The data center industry is undergoing a seismic shift. As AI workloads and hyperscale architectures push Ethernet speeds from 400G to 800G and now toward 1.6T, the per-lane data rate has escalated from 56G PAM4 to 112G PAM4 and, increasingly, to 224G PAM4. At these speeds, the passive interconnect — connectors, cables, and PCB traces — is no longer a transparent conduit. It has become the dominant performance bottleneck and the most critical element in the signal integrity chain.
This article provides a comprehensive guide to the testing methodologies, material selection criteria, and design trade-offs that engineers and procurement teams must navigate when specifying connectors and cables for 112G and 224G SerDes links. Whether you are a signal integrity engineer validating a next-generation switch, or a sourcing manager evaluating OSFP and QSFP-DD cable assemblies, this guide bridges the gap from “it connects” to “it measures up.”
What Are 112G and 224G SerDes, and Why Do They Matter?
The Basics of PAM4 Signaling at 112G and 224G
A Serializer/Deserializer (SerDes) converts parallel data into a high-speed serial stream and back again. At 112G, each electrical lane runs at 106.25 Gbaud using PAM4 (Pulse Amplitude Modulation with 4 levels), delivering approximately 100 Gbps of usable data throughput after FEC overhead. At 224G, the baud rate doubles to 212.5 Gbaud, supporting roughly 200 Gbps per lane.
PAM4 encodes two bits per symbol using four distinct voltage levels. The vertical eye opening shrinks by a factor of three compared to NRZ, making the link extremely sensitive to noise, jitter, insertion loss, and crosstalk — all of which are heavily influenced by the passive channel.
Industry Standards Driving Adoption
The OIF (Optical Internetworking Forum) has been at the forefront of defining interoperability specifications:
- CEI-112G-VSR/MR/LR: Covers chip-to-module, chip-to-chip, and long-reach backplane channels at 112G.
- CEI-224G-VSR/LR: Extends the framework to 224G, with demonstrations at OFC 2024 and OFC 2025 showcasing multi-vendor interoperability across connectors from Amphenol, TE Connectivity, Molex, and Samtec.
IEEE 802.3 is simultaneously developing 200GbE and 1.6TbE standards, while the Ethernet Alliance hosted its first 200 Gbps/lane interoperability plugfest in late 2025, validating OSFP-XD and QSFP-DD1600 interconnects.
How Do Connectors Impact Signal Integrity at 112G and 224G?
Insertion Loss: The Primary Constraint
At 112G PAM4, the Nyquist frequency is approximately 26.6 GHz. At 224G PAM4, it rises to 53.125 GHz. Every millimeter of connector contact, every via transition, and every impedance discontinuity contributes to insertion loss. The OIF CEI-224G-LR specification targets an end-to-end channel loss budget of ≤ 40 dB, which must be distributed across packages, PCB traces, connectors, and cables.
For a typical 224G long-reach link with two connectors and a 1-meter backplane or cable, the connector pair alone may consume 2–4 dB at the Nyquist frequency. This leaves very little margin for PCB routing and package escape.
Return Loss and Impedance Discontinuities
High-speed connectors must maintain a tightly controlled 100 Ω differential impedance across the entire bandwidth. Even small deviations — caused by pin-to-pad transitions, via stubs, or mating interface tolerances — create reflections that degrade the signal eye. At 224G, the wavelength at 53 GHz is approximately 2.5 mm in FR-4 equivalent media, meaning sub-millimeter discontinuities become electrically significant.
Crosstalk: Near-End and Far-End
Dense connector arrays, such as those found in OSFP and QSFP-DD form factors, pack 8 differential pairs into a compact footprint. At 224G frequencies, far-end crosstalk (FEXT) becomes a dominant impairment. Connector vendors now routinely specify crosstalk performance out to 67 GHz and beyond, and advanced shielding geometries are essential.
What Role Do Cables Play in 112G/224G Interconnects?
Passive Copper Cables (DACs) vs. Active Electrical Cables (AECs)
Direct Attach Copper (DAC) cables are the lowest-cost, lowest-latency option for short-reach connections (typically < 2 m at 112G). However, at 224G, the usable reach of passive DACs shrinks dramatically due to frequency-dependent conductor loss and dielectric loss. Industry demonstrations at OFC 2025 showed 224G OSFP DAC assemblies from TE Connectivity, Molex, and Amphenol operating over limited lengths.
Active Electrical Cables (AECs) embed retimer or redriver ICs within the cable assembly to regenerate the signal, extending reach beyond 2 meters at 112G and enabling practical 224G copper connectivity. The OIF CEI-224G-LR demo at ECOC 2024 demonstrated 224G PAM4 transmission over a network of multi-vendor connectors and AECs totaling over 25 dB of channel loss and 40 dB of insertion loss die-to-die at 56 GHz.
Cable Construction and Shielding
For 112G and 224G applications, twinaxial cable pairs must exhibit:
- Low skew (< 1 ps/inch intra-pair)
- Consistent impedance (100 Ω ± 2 Ω)
- Low loss tangent dielectric insulation to minimize high-frequency attenuation
- Robust shielding to limit alien crosstalk between adjacent pairs
Vendors like Samtec, Amphenol, and TE Connectivity offer specialized cable assemblies using Flyover and OverPass architectures that bypass the lossy PCB entirely, routing high-speed signals directly from the chip site to the I/O port via low-loss cabling.
How Do You Select the Right Low-Loss PCB Laminate for 112G/224G Channels?
Understanding Dk and Df
Two material properties dominate PCB performance at high frequencies:
- Dk (Dielectric Constant): Determines signal propagation speed and trace geometry. Lower Dk values allow wider traces on thinner layers, reducing skin-effect loss and extending bandwidth. For 224G channels, Dk values in the range of 2.8–3.2 (at 10 GHz) are typical for ultra-low-loss laminates.
- Df (Dissipation Factor / Loss Tangent): Directly governs dielectric loss, which becomes the dominant loss mechanism at frequencies above 20 GHz. For 112G applications, Df values below 0.003 are commonly specified. For 224G, the industry is pushing toward Df < 0.001 — a threshold that AGC (formerly Asahi Glass) and other material suppliers have demonstrated in laboratory settings.
Material Tiers for High-Speed Design
| Material Tier | Typical Df (10 GHz) | Application | Example Products |
|---|---|---|---|
| Standard Loss | 0.018–0.025 | ≤ 25G NRZ | FR-4, standard polyimide |
| Mid Loss | 0.008–0.012 | 56G PAM4 | Megtron 4, TU-768 |
| Low Loss | 0.003–0.005 | 112G PAM4 | Megtron 6, EM-890K, TU-872 |
| Ultra-Low Loss | 0.001–0.003 | 224G PAM4 | Megtron 7, EM-891K2 |
| Extremely Low Loss | < 0.001 | 224G+ / 448G R&D | AGC experimental, PTFE hybrid |
Copper Roughness: The Hidden Loss Factor
On ultra-low-loss laminates where Df is minimized, copper roughness becomes the dominant loss contributor. Standard electrodeposited (ED) copper has an Rz roughness of 3–6 µm, which significantly increases conductor loss at 224G frequencies. Reverse-treated foils (RTF) and hyper-very-low-profile (HVLP) foils with Rz < 1.5 µm are increasingly specified for 224G PCB designs.
What Does 112G/224G Connector and Cable Testing Look Like?
Key Test Parameters
Testing connectors and cables for 112G/224G compliance requires characterization across a broad set of parameters:
- S-Parameter Measurements (S21, S11, SDD21, SCC21): Performed using vector network analyzers (VNAs) with bandwidth of at least 67 GHz for 224G. Keysight, Anritsu, and Rohde & Schwarz offer instruments capable of single-sweep measurements to 70 GHz and beyond.
- Time-Domain Reflectometry (TDR): Used to identify impedance discontinuities along the signal path. The OIF CEI-224G demo at OFC 2025 featured time-domain network analyzer measurements of cabled near-chip and host connectivity.
- Eye Diagram Analysis: BER testing at 1E-15 or lower (with FEC) is the target for CEI-224G-LR links. High-bandwidth real-time oscilloscopes (≥ 70 GHz analog bandwidth) with software-based FFE and DFE equalization are used to evaluate eye openings.
- Crosstalk Characterization: NEXT and FEXT are measured across all aggressor-victim pair combinations in a multi-lane connector.
Test Fixtures and Launch Connectors
At 224G, the test fixture itself becomes a critical part of the measurement. Amphenol’s TR™ Multicoax Series custom package-top-launched connectors, designed for 112G/224G SerDes development, address challenges such as excessive loss through device sockets, limited signal launch options, and real estate constraints on device substrates. These compression-mount, solderless connectors deliver signal integrity performance past 67 GHz and offer reusability across multiple test programs.
Samtec’s published research on realistic use cases for edge, angled, and vertical launch connectors up to 100 GHz provides practical guidance on optimizing signal transitions from the test instrument to the device under test (DUT).
Compliance Testing and Interoperability
The path from lab validation to market qualification follows a structured process:
- MSA Compliance: OSFP-XD and QSFP-DD1600 MSAs define mechanical, electrical, and thermal requirements that connectors and cable assemblies must meet.
- OIF Interoperability Demos: Multi-vendor demonstrations at industry events (OFC, ECOC, DesignCon) validate real-world interoperability.
- Ethernet Alliance Plugfests: The December 2025 plugfest at Keysight’s Santa Clara campus was the industry’s first major event to test 200 Gbps/lane SerDes interoperability across vendors.
What Are the Key Design Trade-Offs for 112G/224G Connector Selection?
Performance vs. Cost
Ultra-high-performance connectors with sub-millimeter tolerances and advanced shielding come at a significant cost premium. For 112G applications where the loss budget is more relaxed, standard OSFP or QSFP-DD connectors may suffice. At 224G, the tighter loss budget often necessitates premium connector families or alternative architectures like Flyover cabling.
Thermal Management
At 224G, the power dissipation in active cable assemblies and retimers increases. OSFP modules already operate at 25–30 W, and next-generation OSFP-XD modules may push higher. Connector thermal resistance and airflow design become integral to system reliability.
Mechanical Durability
Data center connectors must withstand hundreds of mating cycles without degradation. At 224G, even micro-scale wear on contact surfaces can shift impedance and increase insertion loss. Gold plating thickness, contact geometry, and retention force specifications all require careful evaluation.
Roadmap Alignment
With 448G SerDes discussions already underway in OIF and IEEE, selecting a connector platform that can scale beyond 224G protects the investment. Connector families that demonstrate a clear bandwidth roadmap — such as those supporting measurements to 100 GHz — offer better long-term value.
Who Are the Leading Connector and Cable Vendors for 112G/224G?
| Vendor | Key 224G Products | Notable Capabilities |
|---|---|---|
| Amphenol | OSFP, QSFP-DD MCBs, OverPass assemblies, TR Multicoax test connectors | End-to-end 224G channel solutions, OIF demo participation |
| TE Connectivity | OSFP DAC/AEC, near-chip connectors | 224G OSFP MCBs, active copper cable solutions |
| Samtec | Flyover cable systems, ExaMAX, edge/vertical launch connectors | Published 100 GHz connector research, backplane cable assemblies |
| Molex | OSFP, QSFP-DD systems | 224G system architecture guidance, broad connector portfolio |
| Wilder Technologies | OSFP/QSFP-DD MCBs, compliance test boards | Test fixture and MCB solutions for OIF interoperability demos |
What Comes Next? The Road to 448G and Beyond
The industry is already laying the groundwork for 448G SerDes, which would push per-lane rates to 448 Gbps using PAM4 at approximately 225 Gbaud — or potentially explore higher-order modulation. At these speeds, the passive channel challenges multiply:
- Nyquist frequency exceeds 112 GHz, demanding connector bandwidths well beyond current capabilities.
- PCB laminate Df must approach the theoretical limits of hydrocarbon and PTFE-based materials.
- Co-packaged optics (CPO) may bypass the electrical connector entirely for certain link reaches, fundamentally changing the interconnect architecture.
For now, 112G and 224G represent the critical battleground where connector and cable technology must evolve from simply providing a physical connection to delivering measurable, repeatable, and compliant signal integrity performance.
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