25Gbit/s SFP28 & QSFP28 Copper Cable Interconnect Technology Rise


Recent technological advances have made copper cable assemblies an even more viable option for high-speed applications. As Bishop & Associates noted, "Designers prefer to stay with familiar copper interconnect technology and are developing channel design, simulation and board layout expertise that continue to push the bandwidth. Few engineers are willing to predict the ultimate performance limit of copper interconnects.”

Cable integration, power and thermal management are intrinsic challenges in today's data centers populated by enterprise servers and storage applications. Rising bandwidth demands dictate continuous increases in transmission rates. The introduction of 25 Gbit/s channels offers a potential game-changing solution. High-speed copper 25-Gbit/s enabled products in the prototype stage can now deliver a higher bandwidth alternative to traditional copper — at a lower-cost entry point than optical connectivity.

The Copper Connectivity-Optical Fiber Combination

While optical fiber is popular for long-distance network communications, copper connectivity offers cost-effective solutions for short-to-midrange applications. For designers, optical media also poses intrinsic challenges, including thermal and power management.

In contrast, passive copper cables fill the demand for low-cost, low-power, short-range (1-7m) applications and are often the best solution for stand-alone systems. Approximately 90% of applications are ≤5 meters, which includes most data connections in high-performance computing systems.

Network system data centers frequently blend optical modules and copper cable assemblies; savvy designers can readily integrate and optimize systems to leverage the strengths of each. High-speed passive 25 Gb/s copper channels also bring a competitive cost and performance solution to data center cabling — including top-of-rack, middle-of-rack, and connections to storage servers.

Increasing Data Center Capacity within the Same Footprint

High-density cables must retrieve and transmit data from storage rapidly to meet variable and peak demand. But current systems are limited by the front-panel I/O bandwidth density. One way to provide greater data rates is to increase the number of channels; however, front panels are already crowded, so adding additional ports is difficult.

Another way to expand bandwidth is increasing the data-rate of each channel, which enables data centers to grow capacity without additional floor and rack space. Increasing the data rate of each channel also increases port density at the panel.

A passive copper data rate for a single high-speed link of 10Gb/s requires 10 lanes to achieve an effective 100Gb/s data rate. Increasing the rate of each lane to 25Gb/s thus reduces the lane requirement from 10 to four lanes, saving valuable real estate and creating a higher-density front panel I/O.

All aspects of the channel should be assessed for variation across time, process, and temperature. The challenge of interoperable, high-speed electrical performance thus increases exponentially with a linear increase in speed. While 10Gb/s channels allow for margins of error in specifications, interoperability at 25Gb/s does not afford the same buffer, taking the challenge of universal interoperability to new levels.

Increasing Bandwidth to New Levels
In recent years, significant improvements have occurred in connectors, paddle card designs, connector launches, conductor terminations, and raw cables. 100Gb/s copper assemblies from many leading manufacturers integrate design improvements in almost every critical area. For example, some small form-factor, pluggable I/O systems now offer eight lanes at 25Gb/s.

As Figure 1 shows, the differential insertion loss of next-generation 25 Gb/s copper 5m cable assemblies is better than current 10 Gb/s copper 3m cable. Next-generation cable also offers improvements in crosstalk, with approximately 50% less noise than current 3m cable assemblies.

Reducing Crosstalk Noise

Integrated Crosstalk Noise (ICN) shows noise levels in high-speed 5m next-generation cables are approximately 50% less than 3m current-generation counterparts (see Figure 2). Improved ICN leads to improved signal-to-noise ratio, which improves interconnect signal integrity. This gives designers flexibility that is unavailable in current systems.

Passive copper cables use considerably less power than optical modules. At
100G QSFP28 to 4 25G DAC

Passive copper may also reduce the price-per-link by a factor of >3 compared to optical modules and fiber optic cables at ≤7m lengths. In terms of reliability, passive copper cable contains only one electronic component (a single EEPROM) and hence can provide MTBFs 10-50 times longer than an optical cable assembly.

Design Considerations for 25 Gb/s Copper Channel Connections

Tradeoffs are inherent in connectivity selection and design, whether optical fiber or copper transmission, or some combination. Although fiber optics is favored for long runs, copper remains the preferred solution for shorter-cable-length applications. High-speed 25-Gbit/s bandwidth copper makes it an even more attractive alternative. However, there are still unmet challenges between the feasibility and the commercial viability of 25-Gbit/s copper connectivity. Key considerations for designers looking at 25-Gbit/s copper are high-frequency insertion loss and noise, with the primary consideration being the SNR margin. Component vendors are partnering to provide designers accurate and predictive component level models and end-to-end channel models to allow for the appropriate balance of price versus performance in new 25-Gbit/s systems. New Molex products currently under development will further reduce or eliminate noise, fluctuation and other common issues.

 25 Gbit/s Copper Cable Market Is Rapidly Growing

Manufacturers engaged in advancing high-speed copper — as well as industry analysts — recognize the important role of copper and how advanced signal conditioning has extended the serviceable life of existing components, while stimulating the development of next-generation copper interfaces that are viable for large volume production. Copper prototype products currently being vetted and tested and are expected to reach a broader market by year-end 2011, with volume production over the next 3 to 5 years. Total interoperability will require proper component specification, clarity of defined and accepted compliance methods and continued collaboration across all aspects of implementation. The proliferation of cloud, Internet, higher-performance computing applications, server virtualization, and converged networking will continue driving demand for higher-bandwidth blade and rack server connections — all sweet spots for cost-wise and energy-efficient 25-Gbit/s copper connectivity.

Huizhou C-FLINK Technology Co.,Ltd. is a professional manufacturer of Direct Attach Cable, with mature manufacturing technology and advanced manufacturing equipment to provide SFP28 and QSFP28 copper cable with stable performance and superior quality.


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