As networking vendors look to address the bandwidth, throughput and latency demands of AI and high-performance computing, a relatively new method of melding copper connections with optical technology is emerging as a possible way to increase high-speed connectivity options in switches, GPUs and other connectivity gear.
Known as co-packaged copper (CPC), or co-packaged cables in some circles, the basic idea is to take a copper cable straight out of an ASIC and link it with optical fibers, according to Peter Jones, chairman of the Ethernet Alliance. (See also: AI drives high-speed, efficient Ethernet networks)
“There is a lot of interest in CPC. It’s pretty experimental at this point, but CPC is being explored as a potential future solution, particularly for ultra-short reach interconnects within AI accelerators and chiplets,” Jones said.
One issue is that copper can only carry a signal a short distance – in the 4-meter range – whereas straight-up co-packaged optical packages are only limited by the strength of the laser and can be optimized for distances of several kilometers. CPC work is underway to change or adapt to that challenge.
A primary benefit of CPS is its potential to improve ASIC signal integrity and channel loss reduction, allowing longer electrical interconnects for next-generation line rates (400G/lane), experts say. CPC is not needed today for ongoing 200G/lane system deployment; rather, it’s a forward looking package technology for future 400G interconnects.
CPC at DesignCon, OFC
Broadcom and Samtec demonstrated CPC technology at two recent industry events, DesignCon and the Optical Fiber Communication Conference (OFC). Marvell and Amphenol demoed CPC at OFC as well.
Broadcom’s demonstration and a follow-up session explored the benefits of further developing CPC, such as reduced signal integrity penalties and extended reach, through channel modeling and simulations, Broadcom wrote in a blog about the DesignCon event.
“Experimental results showed successful implementation of CPC, demonstrating its potential to address bandwidth and signal integrity challenges in data centers, which is crucial for AI applications,” Broadcom stated.
In addition to the demo, Broadcom and Samtec also authored a white paper on CPC that stated: “Co-packaged connectivity (CPC) provides the opportunity to omit loss and reflection penalties from the [printed circuit board (PCB)] and the package. When high speed I/O is cabled from the top of the package advanced PCB materials are not necessary. Losses from package vertical paths and PCB routing can be transferred to the longer reach of cables,” the authors stated.
“As highly complex systems are challenged to scale the number of I/O and their reach, co- packaged connectivity presents opportunity. As we approach 224G-PAM4 [which uses optical techniques to support 224 Gigabits per second data rates per optical lane] and above, system loss and dominating noise sources necessitate the need to re-consider that which has been restricted in the back of the system architect’s mind for years: What if we attached to the package?”
At OFC, Samtec demonstrated its Si-FlyHD co-packaged cable assemblies and Samtec FlyoverOctal Small Form-factor Pluggable (OSFP) over the Samtec Eye Speed Hyper Low Skew twinax copper cable. Flyover is Samtec’s proprietary way of addressing signal integrity and reach limitations of routing high-speed signals through traditional printed circuit boards (PCBs).
“This evaluation platform incorporates Broadcom’s industry-leading 200G SerDes technology and Samtec’s co-packaged Flyover technology. Si-Fly HD CPC offers the industry’s highest footprint density and robust interconnect which enables 102.4T (512 lanes at 200G) in a 95 x 95 mm chip substrate,” Samtec wrote.
Co-packaged copper vs. co-packaged optics
Other vendors such as Marvell and Cisco are looking at CPO technologies and how they may develop it in the future.
“Co-packaged copper (CPC) technology is an interesting and potentially useful approach to providing switch architecture flexibility as SerDes speeds continue to increase. We see it as an approach to continue to support the pluggable module-based solutions,” said Mark Nowell, Cisco Fellow. “Cisco has been evaluating the technology as it is may reduce the channel losses between an ASIC and a pluggable module for high-speed, high-density switch designs, Nowell said.
CPC products are not seen as particularly competitive products to co-packaged optical technology (CPO) or near-packaged optics (NPO) but rather as related developments to building higher-speed networking gear, experts said. With NPO technology, optical transceivers are placed on the same circuit board as the high-speed electronic chip such as a switch ASIC, GPU, or CPU but in a closely located separate package.
“CPC technology and the CPO technology are somewhat unrelated, and we would consider them adjacent technologies,” Nowell said.
Co-packaged copper is an emerging alternative to co-packaged optics for certain high-speed interconnect applications such as intra-rack or chip-to-chip interconnect in AI data centers, said Sameh Boujelbene, vice president of the Dell’Oro Group. “For example, it can be used to connect co-packaged ASICs and SerDes or to connect compute accelerators (XPUs) and memory modules in disaggregated infrastructure. It offers lower latency, lower power and lower cost than CPO.”
CPC and CPO address different needs and target different interconnects, and CPC and near packaged optics (NPO) are complementary. One can use CPC to get the signals out of the package electrically and connect to NPO located near the package on the board. In addition CPC and NPO will actually be more expensive to deploy than CPO from a CapEx (components costs) and OpEx (power consumption), observers added.
CPO gear, which features the integration of optical components directly into a switch ASIC, currently gets the most attention in the optical community, but the technology is still largely not available in many networking products used to build large networks.
“The companies and institutions working on CPO have made great strides in developing suitable electronic components,” the IEEE wrote in its ComSoc Technology Blog last year. “But hundreds of meters of fiber will be packed into the switch box for the first time, and faceplate connections will have unprecedented densities. As a result, the design and development of optical system solutions will also be critical elements in the success of CPO.”
Source:: Network World