800G Ethernet Technology

Overview

800G Ethernet is a high-bandwidth Ethernet standard that can transmit data rates of 800 Gbps (gigabits per second). It represents the latest advancement in Ethernet technology and is designed to meet the increasing demand for data transmission and the ability to handle large amounts of data.

The 25G and 50G Ethernet Consortium standards provide an 800G implementation specification based on 8 lanex100Gb/s technology, enabling adopters to deploy advanced high-bandwidth interoperable Ethernet technology.

800G Ethernet is mainly used for large data centers, cloud service environments, and applications that require high bandwidth. For these scenarios, it can provide higher speed, greater throughput, and better network performance, thus supporting faster and more efficient data communication.

Architecture

800Gb/s Ethernet technology is designed as an interface that uses eight 106 Gb/s lanes using 2xClause 119 PCSs (400G) to connect a single MAC operating at 800 Gb/s (though the 400G PCSs are modified, this is just a very high-level conceptual view). The following figure shows the high-level architecture.

In the specific implementation process, the 800GBASE-R specification is not simply splicing two 400Gs together but introduces a new Media Access Control (MAC) and Physical Coding Sublayer (PCS) that can achieve 800G with minimal cost. Since the new PCS contains a reuse of the previous PCS, it retains the standard RS (544, 514) forward error correction and provides good backward compatibility features.

PCS/FEC

By utilizing two 400 Gb/s PCSs (including FEC) and supporting 32 PCS lanes (each lane speed is 25Gb/s) to support 800 Gb/s capability. The figure below shows the TX PCS data flow and functionality. 2×16 PCS lanes are generated from two PCS stacks, and then 4:1 bit multiplexing is performed by the PMA to the PMD to create 8x106G PMD lanes.

The figure below is a schematic diagram given by the 800G Pluggable MSA working group in the “800G MSA White Paper”, an 800G implementation scheme that can be quickly launched. By readjusting two 400G PMAs, an 800G PMA is obtained, a low-cost 800G PMD is defined, and an 800G Ethernet based on 8-channel 100Gb/s technology is realized.

Challenges

The current 800G Ethernet implementation uses 8 channels, each channel transmission rate is 100Gbps. This doubles the PAM4 (four-level modulation) speed from the previous generation of 50Gbps to 100Gbps. The next-generation 800G transceiver under development will make the rate of each channel reach 200Gbps, which brings significant challenges because it requires both higher-order modulation and PAM4 data rates to be increased.

High-speed SerDes and power consumption

To support the increase of the overall bandwidth of the switch chip, the speed and power of SerDes are also increasing. Currently, the SerDes speed has increased from 10Gbit/s to 112Gbit/s. However, SerDes power consumption has become important to the system’s total power consumption. The next-generation switch chip will double the bandwidth again because the 102.4T switch will have 512 200 Gb/s SerDes channels. These silicon switches will support 800G and 1.6T on 224 Gb/s channels.

Solution:

Higher-speed SerDes: Research and develop higher-speed SerDes technology to meet the growing data transmission demand. This includes increasing the speed, reducing the power consumption, and improving the signal integrity of SerDes. Power consumption optimization: Adopt a power consumption optimization design method to reduce the power consumption of SerDes. This includes using advanced CMOS processes and low-power circuit design.

Pulse Amplitude Modulation

The current phase of 800G Ethernet employs a higher-order modulation technique that uses PAM4 (4-Level Pulse Amplitude Modulation) to transmit data so that each symbol carries multiple bits of information, thereby increasing the data transmission rate.

Higher-order modulation increases the number of bits per symbol and provides a trade-off between channel bandwidth and signal amplitude. PAM4 modulation is backward compatible with previous generations of products. It offers a better signal-to-noise ratio (SNR) compared to higher modulation schemes, thus reducing the overhead of forward error correction (FEC) that causes latency.

Solutions:

Better analog front-end (AFE): Research and develop higher-performance analog front-ends to support higher-order modulation schemes. This may include more accurate clock recovery, lower jitter, and better signal processing capabilities. Advanced equalization techniques: Use innovative digital signal processing (DSP) and equalization techniques to overcome distortion and noise in the channel. This helps improve the reliability of PAM4 signals. Explore higher modulation schemes: Although PAM4 is widely used in the current 800G Ethernet, future standards may adopt higher-order modulation schemes, such as PAM6 or PAM8. This will increase the transmission rate per symbol and bring higher complexity.

How to reduce the bit error rate (BER) of 800G Ethernet?

In high-speed data transmission, the signal is affected by various interference and attenuation factors when passing through the channel. These include signal attenuation, noise, crosstalk, and other signal distortion factors. These factors cause bit errors in the signal, i.e., BER. In data transmission, the presence of BER may cause serious data corruption, reducing the availability and integrity of data. In previous high-speed data standards, such as 100G Ethernet, conventional fine-tuning equalizers and signal processing techniques were sufficient to reduce BER. However, in the higher-speed 800G Ethernet, more complex methods are needed to cope with the higher BER challenges. Forward error correction (FEC) is widely used to reduce BER. It involves adding redundant information in data transmission to help the receiver detect and correct transmission errors. FEC algorithms add redundant bits in data frames, enabling the receiver to reconstruct lost or damaged data bits. This helps improve the reliability of data transmission, especially in high-speed networks.

In the later development stages, such as 200Gb/s systems, more complex FEC algorithms are needed to cope with the higher BER challenges. These algorithms may include using more redundant data and more sophisticated error correction mechanisms to ensure the reliability of data transmission.

How to improve the energy efficiency of 800G Ethernet?

Improving the energy efficiency of 800G Ethernet is an important challenge, especially in large-scale data centers. Although the optical module design has become more efficient, reducing the power consumption per bit, the overall power consumption of the modules is still a serious issue, as large data centers usually have tens of thousands of optical modules. One way to solve the power consumption challenge of optical modules is to use co-packaged optical devices. This technology integrates the optoelectronic conversion function within the package of the optical module, reducing the power consumption of each module. Co-packaged optical devices can provide various advantages, including higher energy efficiency and smaller package sizes.

What are the benefits of 800G Ethernet?

• Increased bandwidth and data speed: With the rapid development of technologies such as big data, artificial intelligence, cloud services, etc., data traffic is constantly increasing. Most importantly, 800G Ethernet can handle more data streams and network connections simultaneously. In addition, 800G Ethernet achieves faster data upload, download, and transmission, improving data processing efficiency and user experience. With the increase in bandwidth and data speed, 800G Ethernet supports high-density and large-scale data transmission, while ensuring the stable and efficient operation of the network.
• High-performance computing field: In high-performance computing applications, such as scientific computing and artificial intelligence training, high-speed data transmission and processing capabilities are required. 800G network improves data transmission speed and higher network performance, to maintain the operation of high-performance computing tasks. This is very important for applications that handle large-scale complex calculations, such as scientific research, big data analysis, and artificial intelligence training. Introducing 800G Ethernet will further promote the innovation and development of the high-performance computing field.
• Support large-scale data centers: Data centers are key places for storing and processing large amounts of data. The emergence of 800G Ethernet technology can significantly improve the performance of data centers, accelerate data transmission speed and processing capabilities, and provide higher throughput and lower latency for data centers. In summary, 800G Ethernet plays an extremely important role in the current network environment, representing the future development trend of network technology.

The current status of 400G/800G Ethernet products

Note: The data in the table above mainly comes from the product introduction pages of various manufacturers’ official websites (December 2023).