With ever increasing bandwidth needs for video conferencing, streaming, digital entertainment, 5G, autonomous vehicles, trading, IoT etc., both electrical and optical links in the Data Center continue to move upward in throughput and data rate.
Current projects from the Institute of Electrical and Electronics Engineers (IEEE) and the Optical Internetworking Forum (OIF) standards associations are addressing the next generation in speed – 800G or 100G / lane.
This application note will cover the changes in requirements between 400G and 800G electrical interfaces and how Keysight Technologies Transmitter and Receiver Conformance Test Solutions allow users to easily perform design validation testing and explore their design margins.
Table of Contents
The move from 100G to 400G links was a revolutionary change going from NRZ (1 bit/symbol) to PAM4 (2 bits/symbol) signaling, bringing with it a number of new issues and consequently new measurements such as PAM4 linearity, signal to noise and distortion ratio (SNDR) and new test methods for eye height, eye width, VEC (vertical eye closure), etc.
The latest evolution to 800G may not seem that significant, since there are already 400G optical transceiver links running at 100G / wavelength (53 Gbaud PAM4) e.g. 400GBASE-DR4, 400G-FR4. However, the electrical lanes for these and all other 200 and 400G standards to date have operated at 50G / lane utilizing 8 x lanes at 26 Gbaud PAM4 per lane e.g. 400GAUI-8.
Current developments from the IEEE and OIF standards associations are addressing the next generation 800G Ethernet. Projects such as IEEE 802.3ck and OIF-CEI 112G specify the electrical link parameters and test methods for 53 Gbaud PAM4 and 38-58 Gbaud PAM4 respectively, based on 8 x PAM4 lanes, bringing 100G / lane to the electrical interfaces such as chip-to-module, chip-to-chip, backplane, and copper cable.
Although IEEE and OIF standards are highly leveraged from each other, there are some differences in parameter definitions and measurement methodology. Also, as baud rates increase so do losses in the transmission channel, leading to smaller and more distorted PAM4 signals. This necessitates changes to parameter definitions and test methods even from the previous 400G (50G / lane) standards.
OIF CEI-112G-VSR, -MR, and -LR have an equivalent clause in IEEE 802.3ck as shown in table 1.
It generally takes a few years for a standard to progress from conception to being finalized and released. The physical layer aspects are usually complete well before the standards are final and it is essential for early adopters and test solution providers to be closely involved in the creation of these standards to ensure that the key parameters and test methods developed are both achievable and repeatable.
800G Design Cycle
Keysight Technologies is uniquely positioned to offer test and measurement solutions throughout the entire design cycle, from simulation, design validation, conformance test, protocol test, and manufacturing. With close association and participation in the standards organizations, Keysight is able to provide first-to-market Conformance Test Solutions that can be updated as changes occur during the standards creation, allowing timely characterization and validation of component and systems designs to run concurrently with the standards development cycle.
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