Although many domestic and foreign companies claim to have developed 400G products, does this booming scene mean the arrival of 400G era? In fact, 400G technology is not mature yet. As the external interface of the server, the upgrade of optical module rate is system engineering, and 400G optical module still faces many challenges.
Challenge 1:
It will take some time for the server data processing bandwidth to improve
In terms of demand, the application of 400G optical module is driven by the increase of server data processing bandwidth.
Only when the server data processing bandwidth reaches 100G can the interconnection between switches reach 400G (4*100G), while the PCIe 4.0 standard of 100G server data processing bandwidth is frozen at the end of 2017, and 400G commercial scale is still more than a year away.
Challenge 2:
It will take some time to upgrade the switch chip and electrical interface technology
In terms of technical implementation, the connection of 400G optical module requires not only the upgrade of optical communication technology, but also the corresponding upgrade of switch chip and electrical interface technology.
On the one hand, switch chips usually use Broadcom chips, from the sample of Broadcom chips of each generation to the scale shipment of corresponding rate optical modules, the interval is about 2 years, during which it is used for debugging switch chips and optical devices. On the other hand, the 400G optical module needs to use PAM4 modulation to raise the single-channel rate to 56G on the optical side, and the corresponding electrical side also needs to support single-channel 56G. When upgrading to a higher rate, the electrical signal interface must be upgraded accordingly. In general, the connection of the high-speed electrical interface adopts SerDes (serial disintegrator) technology and complies with CEI (general electric interface) standard. Now, CEI 4.0, which enables up to 58 GB/s connectivity, will be released at the end of 2017, and it will be some time before SerDes chips are ready for commercial use.
Challenge 3:
It will take some time to overcome the challenges of different packages
In terms of packaging standards, currently 400G optical modules mainly include CFP8, OSFP, QSFP-DD, COBO, etc., among which QSFP-DD and OSFP are expected to become the mainstream packaging. Now, although some suppliers have introduced 400G optical module samples, but different packages of 400G optical module are facing a variety of challenges, such as QSFP-DD laser due to uneven heat dissipation or late failure, OSFP cannot be backward compatible and so on.
