In this article, we’ll discuss the recent 200+G PAM4 per-lane interconnect developments supported by various consortia, standards bodies, and new product announcements. 

The latest 2023 Ethernet Alliance Roadmap shows the demand for 200+G per-lane pluggable modules, connectors, copper, and optical cable products by 2025. Based on their chart below and the interface roadmap, several different lane-count versions will be implemented using various link products. This includes the new 16-lane OSFP-XD connector that will support 3.2T links.

The 4-lane Ethernet link and interconnect (such as QSFP) were mainly used between 2010 and 2019. However, there is volume potential for the 8-lane QSFP-DD and OSFP links, as well as the 16-lane OSFP-XD links through 2026. This is especially true for supporting newer Radix switch topologies.

Ironically, the current OSFP-XD serial IO interface design uses a 32-copper twin-axial elements cable, which is about the same diameter bundle size as the 34-copper twisted-pair cable that supported many passive parallel IO interfaces 22 years ago.

In the past, fanfare was made about the 1-Gigabit per second Ethernet and FibreChannel era and using simple 1-lane two twin-ax connectors and cables, like the HSSDC1&2 and SFP types. A similar type of reaction might be expected for upcoming developments.

In general, the 32-lane 64 twin-ax next-generation solutions seem unsuitable because of external short-reach active electrical, copper-cable diameter size, and minimum bend radius problems. And it looks like it would be challenging to route internal 32 and 64 twin-ax flat cables per port in a small switch with a 36+ ports faceplate. But it’s possible such designs could be done with airflow and other cost disadvantages.

A few external designs have already incorporated several round cable legs (instead of one). So, will a next-generation 400G per-lane specification be needed to support short-reach active electrical copper links? Or will the market strictly support optical single and multiple lambda links…and will they be primarily used for short-reach chip-to-chip?

At the very least, it’s likely the use of multiple wavelengths of light in one fiber will soon replace or at least reduce the use of many copper wires because of lane growth and reach shrink.

The above graph is the current LINK roadmap, courtesy of the EA website. It will require updating as the 800GbE, 1.6TbE, and 3.2TbE link products develop and get installed in data centers.

QSFP–DD MSA is a consortium focused on new QSDP-DD1600 connector, cable, and module specifications. This application set uses 200+G serial PAM4, 8-lane ports, and 1.6TbE network links. This new technology maintains backward compatibility and supports the latest CMIS specification. The QSFP-DD riding heatsink feature will also be implemented.

We suggest reading the QSFP-DD MSA Rev4.0 PDF is available at qsfp-dd.com.

It’s worth noting that the QSFP-DD and OSFP connector and cage designs have been improved over the last four years to support increasing transmission rates. Certain pluggable connectors and cabling products only support 25G NRZ or 56G PAM4 and potentially use older production tooling.

Essentially, users should be aware of what connector revision they choose for their 56G PAM4, 100+G PAM4, and 200+G PAM4 speed rate per-lane applications. Newer connector designs have improved airflow features, thermal design, higher wattage capacity, minimized termination zones, and electrically tuned structures. Most external copper cables’ impedances are 100 Ohm while internal cables are usually 92 Ohm.

TheIEEE-802.3df Ethernet Task Force working group is progressing on its objective to support various link reaches. These objectives include supporting 200G per-lane optical and copper connectors and cables for long and short-reach applications.

The simulations are promising and new data measurements will be available at this month’s meeting in San Antonio, TX. It seems most backplanes running at 224G PAM4 will be cabled and not PCB types.

The depicted 27 and 29awg wire gauges are rarely used in applications, so a new raw cable tooling investment will be necessary for some suppliers. Below is a look at the approved topologies to date from two presentations found in their public records…

Here are some additional slide presentations with more details…

The Optical Internet Forum (OIF) offers several CEI-224G developments and specifications. Many members are also a part of the IEEE-802.3df 212G Ethernet group. IB also follows OIF spec development.

InfiniBand (IB), XDR 224G per-lane specification rev 1.7 is currently in development but closely following the OIF CEI 224G spec. InfiniBand’s spec rev 1.6 supports the new class of Radix switches with 256 HCAs. Their roadmap has forecast that the 200G-per-lane XDR would likely launch in the last quarter of 2024. It indicates that the 400G per-lane GDR will come out in 2028. 

The roadmap of the 256 Switch Radix topology is below. It suggests lower cable and pluggable connector use in new or upgraded data centers.

DesignCon 2023 attendees saw several new 200+G PAM4 per-lane copper and optical products demonstrations.

For example, TE Connectivity demonstrated a near-chip connector and cable running well at 224G PAM4 per lane. These low-profile AdrenaLINE connectors are used on the cable assembly end of an internal pluggable receptacle or faceplate. Also, the ASIC chip over-the-board Catapult jumper cables are replacing the more costly PCBs, along with their substrate issues. This demonstration included using TE’s prototype OSFP-224 connector and cage. 

The Intel FPGA 224G PAM4 Serdes chip is showcased below.

TE also demonstrated its new microSFP+ Pluggable connector systems that support new industrial Ethernet applications.

SAMTEC showcased its 54 copper 224G PAM4 per-differential pairs using its proof of concept SI-FLY Gen 2 connectors and 32-guage cable assemblies at OFC 2023.

Marvell demonstrated its Nova 1.6T PAM4 electro-optics DSP chip platform that supports 200G per optical lambda links and pluggable modules. Newer Radix switch applications are part of Marvell’s targeted market segments. The Nova platform is enabling a 1.6T OSFP-XD optical transceiver module rollout.

OpenLight introduced the new 224G PAM4 InP-based modulator, advancing PIC designs supporting multi-lane DR and FR applications. The product supports 224G per wavelength without increasing cost. OpenLight’s future roadmap includes 448G per-wavelength devices for next-generation QSFP-DD and OSFP-XD pluggable modules.

Observations
Expect several newer product announcements with 200+G per-lane interconnection performance and interoperability for multiple market applications this year. New specifications are slowly being rolled out as the industry validates compliance. Most research is currently focused on developing optical 6.4+T links.

There are also private group efforts to specify smaller pluggable connectors, unlike the current QSFP-DD, OSFP, and OSFP-XD families.

Several top suppliers are offering proprietary, advanced connector solutions for 1U box IO faceplates with near-chip density and thermal circuit performance. Quality optical, signal, and power integrity performance data is sought for many new 200+G links supporting twin-axial electrical and fiber-optic wavelength applications.

Some forecasting and real-time shipment reports indicate a slowdown in Ethernet sales for 2023, with healthy growth in 2024 and 2025.

Currently, users are slowing down 200G development. The focus is on new IO solutions and technologies with different costs and products. Additionally, it’s important to ensure 200+G per-lane products are measured, industry specifications released, and plugfest compliance-interoperability and third-party certifications are in place.

Although the below LightCounting finding suggests decline, we can likely expect (and enjoy) new developments and growth next year.