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100G Packaging Technology: QSFP28 vs SFP-DD vs DSFP

NADDOD Edward Jan 16, 2023

In the global market, the 10GE/25GE access rate of servers is still the mainstream. As the data center fabric evolves from 100GE to 400GE, it is expected that 100GE servers will be gradually commercialized, and the main application scenario will be GPU clusters. In the evolution stage of server access, servers with a rate of 50GE will not occupy the mainstream market, and will directly evolve from 25GE to 100GE access, satisfying the current development trend of high throughput and large bandwidth.

QSFP28 Package Introduction

The QSFP28 (Quad Small Form-factor Pluggable) package
type is produced to meet the requirements of 100G applications. It can support 4-channel transmission at the same time. The data rate of each channel is 25Gbit/s, and the transmission rate of 100Gbps is achieved through 4 channels. It is currently Mainstream 100G module package type. It can meet the application requirements of 100G Ethernet (4×25Gbps) and EDR InfiniBand. But the existing QSFP28 interface also has its limitations.

The current mainstream network card of the server is 10GE/25GE network card, and there are also a small number of 100GE QSFP28 network cards. The 100GE QSFP28 network card port is composed of four 25GE physical channels, and can only be adapted to switches with 100GE QSFP28 interfaces. Currently, the industry’s highest-density 100GE QSFP28 TOR access switch contains 32 100GE QSFP28 interfaces. The bandwidth of the switch does not exceed 3.2T, and it can only provide access to 32 servers at most. It cannot meet the high throughput and large bandwidth requirements of 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 Interfaces: SFP-DD and DSFP
100G

Based on the development trend of high throughput and large bandwidth in data centers, server NICs and access switches are evolving to next-generation 100GE interfaces. 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.

Introduction to SFP-DD Package
The SFP-DD (Small Form-factor Pluggable-Double Density) packaging form was proposed by Alibaba at OFC in 2017. Under the initiative and promotion of Alibaba, the SFP-DD MSA organization was announced on July 12, 2017. The goal of the SFP-DD MSA organization is to formulate optical interface standards, mechanical structures and heat dissipation standards for server and switch connections in next-generation 400G data center networks.

The SFP-DD package replaces the traditional 4-lane data center module with 2 lanes, runs up to 25Gbps NRZ modulation or 56Gbps PAM4 modulation, provides solutions up to 50Gbps or 112Gbps PAM4 aggregation, and can even provide 200G required by next-generation data centers in the future (2*100G) and other access solutions save space for the erection of data centers and meet the requirements of low cost, small size, high density and low power consumption of next-generation data centers.

The SFP-DD package is backward compatible with the current SFP/SFP+ package high-speed interface solution, which lays the foundation for the smooth upgrade of the 25G SFP28 AOC solution to 100G, and also establishes a basic technology platform for the upgrade of the single optical port from 50G to 100G. The combination of SFP-DD and QSFP-DD can form a complete solution for data center network 100G access and interconnection between 400G switches.

DSFP Package Introduction
The DSFP (Dual Chanel Small Form-factor Pluggable) MSA standard defines 10G point-to-point application optical modules. It is a dual-transmission and dual-reception optical module, supports two electrical lanes (Electrical lanes), is compatible with the SFP+ packaging specification, and can provide high-density, low-cost optical module solutions for 5G networks. The installation density of DSFP is twice as high as that of SFP, and it is compatible with existing SFP specifications.

DSFP can support up to 28Gbps through NRZ format, and can support 56Gbps per electrical channel transmission through PAM4, and its number of channels is twice that of existing SFP channels. DSFP will therefore be able to support 56Gbps NRZ or 112Gbps PAM4 transmission, and will also support PAM4-based 224Gbps transmission in the future.

DSFP is a new standard that is low-cost, has superior high-speed signal integrity, helps reduce PCB size, and is easy to design and produce. It will better promote the deployment of 5G and protect customers’ investment. After the communication equipment adopts DSFP products, because the module density is doubled, the port density and throughput of the communication equipment are doubled, and the cost performance of the equipment is correspondingly improved, which increases the product competitiveness of customers. Currently, the H3C S9855 series switches on the market have DSFP ports, and NVIDIA (NVIDIA) also has network cards and switches with DSFP ports that can be used with DSFP AOC cables.

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