Trend analysis of 100ge access technology in data center

With the rapid development of big data, distributed storage, AI and high-speed computing, the scale of data center has increased sharply. IDC predicts that the total amount of global data will reach 47 ZBS (1zb = 1 billion TB = 1 trillion GB) in 2020 and 163 ZBS in 2025. Service providers and major enterprises urgently need to speed up the internal switching system of the existing data center from 10GE / 40ge to 100ge / 400ge, and evolve the server access from Ge / 10GE to 25ge / 100ge, so as to meet the current development trend of high throughput and large bandwidth.

In China, Internet enterprises with rapid data business growth have started to deploy 25ge servers on a large scale since 2017; Enterprise customers and some financial customers have also started deploying 25ge servers this year. At present, the 10GE / 25ge access rate of the server is still the mainstream. As the data center fabric evolves from 100ge to 400ge, it is expected that 100ge servers will be deployed from 2020 and reach large-scale commercial use around 2021. The main application scenario will be GPU cluster. In the evolution stage of server access, 50ge servers will not occupy the mainstream market, and will directly evolve from 25ge to 100ge access.

Limitations of existing 100ge qsfp28 interface

At present, the mainstream network card of the server is 10GE / 25ge network card, and there are also a small number of 100ge qsfp28 network cards. The port of the 100ge qsfp28 network card is composed of four 25ge physical channels, which can only be adapted to the switch with 100ge qsfp28 interface. At present, the 100ge qsfp28 tor access switch with the highest density in the industry includes 32 100ge qsfp28 interfaces. The switch bandwidth does not exceed 3.2T, and can only provide access to 32 servers at most. The uplink bandwidth does not exceed 100ge, and does not have the ability of 400ge uplink aggregation, which can not meet the requirements of high throughput and large bandwidth in the data center. It can be seen that the existing 100ge qsfp28 interface is not conducive to the deployment of 100ge servers in the data center.

Next generation 100ge interface

Based on the development trend of high throughput and large bandwidth in data center, server network card and access switch are evolving to the next generation 100ge interface. The next generation 100ge interface consists of two 50ge physical channels. Compared with the previous generation qsfp28 interface, the number of physical channels is halved, and the port density is improved.

At present, the next generation 100ge interface has two packaging options: sfp-dd and dsfp:

1) Sfp-dd (small form factor pluggable double density) is a packaging type mainly promoted by Alibaba and other enterprises, which is twice the density of SFP interface and remains downward compatible with SFP family modules.
2) Dsfp (dual Chanel small form factor pluggable) is a packaging type initiated and promoted by individual equipment manufacturers. Many control and indicator pins are cancelled, and software is used to read and write registers for communication and control.
Category pin signal integrity power supply and its reliability working reliability downward compatibility follow-up development direction
Compared with SFP, the number of pins of sfp-dd is doubled, which is conducive to the fan out of high-frequency signals. The same GND reference plane can be used. The Si has good reliability, more power and ground pins, strong overcurrent capacity and good reliability. Several hardware control and alarm pins are reserved, with high reliability and downward compatibility. It supports the SFP encapsulated optical module and supports smooth expansion

Dsfp adds two pins, which is not conducive to the fan out of high-frequency signals. Different GND reference planes must be used. The reliability of Si is poor and the power supply and ground are tight. Generally, all hardware control and alarm pins are deleted and only IIC communication is reserved. The optical module only works in the full software mode, which is easy to cause system faults and problems, has low reliability and does not have any downward compatibility, which is similar to patching.

Based on the above comparative analysis, it can be seen that the best choice for 100ge access to the data center is to use sfp-dd packaging technology. ZTE followed the trend and launched a tor switch with large capacity and high density for the next generation of 100ge server access. Its switching capacity is up to 8tbps, providing 48 100ge ports for server access and 8 400ge ports for uplink aggregation. Different from the existing 100ge qsfp28 access switch, the next generation 100ge access switch adopts the 100ge interface encapsulated by sfp-dd. the 100ge port is composed of two 50ge physical channels, and the 400ge port is composed of eight 50ge physical channels. The whole machine includes 160 50ge physical channels, which greatly improves the 100ge port density of 1U equipment.