What Are the Common 400G QSFP-DD Transceiver Types in the Market?

Posted on Jul 11, 2023

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The continuous growth in global data traffic has promoted data centers to upgrade from 100G to 400G networks. 400G optical modules, as the most common high-efficient and cost-effective solution to 400G network, can greatly improve system performance, fasten transmission speed, broaden bandwidth, and reduce broadband costs. Therefore, this article will mainly introduce 400G QSFP-DD optical modules from the aspects of form factors, application scenarios, FAQs, and future trends.

Common 400G QSFP-DD Transceiver Types

Generally, there are eight common 400G QSFP-DD transceiver types in the market. Here will describe the basic information of QSFP-DD SR8, QSFP-DD DR4, QSFP-DD XDR4, QSFP-DD FR4, QSFP-DD FR8, QSFP-DD LR4, QSFP-DD LR8, and QSFP-DD ER8.

400G QSFP-DD SR8

The 400G QSFP-DD SR8 is a four-channel, hot-pluggable optical module that supports MMF links up to 70m (OM3) or 100m (OM4) with an MPO-16 connector, making it ideal for short-distance interconnection. It complies with QSFP-DD MSA specification and IEEE 802.3bs protocol and includes eight parallel transceiver lanes, each of which is capable of a transmission rate of 53.125 Gbps (PAM 4), to transmit data rates of 400 Gbps.

400G QSFP-DD DR4

The 400G QSFP-DD DR4 achieves a max transmission distance of 500 meters on 1310nm center wavelength over SMF with an MPO-12 connector. DR4 stands for "Dense Wavelength Division Multiplexing (DWDM) 4-lane", which means that the 400G DR4 module uses four optical lanes to transmit data, each of which is capable of carrying data at a rate of 106.25Gbps (PAM4), reaching a 425G transmission rate.

400G QSFP-DD XDR4

The 400G QSFP-DD XDR4 is an extended version of the 400G QSFP-DD DR4 optical module, of which transmission distance is longer than QSFP-DD DR4, supporting a maximum link up to 10km over SMF with MTP/MPO-12 connector, complying with IEEE 802.3bs protocol and QSFP-DD MSA standard. And it has four parallel transceiver lanes, which allows a total transmission rate of 400G.

400G QSFP-DD FR4

The 400G QSFP-DD FR4 (stands for "Full Duplex 4-lane, Retimed 4-level" ) is a 400Gbps hot-pluggable transceiver and supports SMF links up to 2km reach over duplex LC connectors. The 400G FR4 transceiver incorporates 4 independent lanes on CWDM4 center wavelengths running at 100Gbps per lane, follows a protocol of 100G Single Lambda MSA specification, and can be used in data centers to provide high-speed data transmission. The single-wavelength transmission rate based on PAM4 modulation can reach 106.25Gbps, achieving a total transmission rate of 400G.

400G QSFP-DD FR8

The 400G QSFP-DD FR8 module adopts the same 50G PAM4 modulation technology as the 400G QSFP-DD SR8. It uses eight optical lanes to transmit data and can reach a maximum transmission rate of 400Gbps. However, unlike SR8, which only fits short-distance transmission, 400G FR8 can be applied in long-distance transmission, with a maximum transmission range of 2km.

400G QSFP-DD LR4

The 400G QSFP-DD LR4 is a high-speed, high-bandwidth, and long-distance transmission transceiver, appropriate for application scenarios like 400G ethernet and data center interoperability. It supports SMF links to 10km over duplex LC connectors and complies with IEEE 802.3bs protocol and QSFP-DD MSA standard.

400G QSFP-DD LR8

The 400G QSFP-DD LR8 also adopts 50G PAM4 modulation technology as SR8 and FR8 and has eight parallel transceiver lanes. However, in contrast to SR8 and FR8, each lane allows longer transmission distances of up to 10km over SMF with duplex LC connectors and has a maximum transmission rate of 106.25Gbps, for a total of 425G.

400G QSFP-DD ER8

The 400G QSFP-DD ER8 has the same transmission rate, modulation technology, and connector as QSFP-DD LR8. It complies with IEEE 802.3cn protocol and QSFP-DD MSA standard. The only difference exists in the transmission distance. The ER8 can achieve a maximum transmission distance of 40km, making it more adapted to ultra-long-distance data transmission.

400G QSFP-DD Optical Modules Application Scenarios

As a low-cost, low-power optical connection solution in the next-generation data centers, 400G QSFP-DD series optical modules are widely used in data centers, metropolitan bearer network, and long-distance high-capacity transmission.

400G QSFP-DD Data Center Direct Interconnection

In the data center architecture, the connection between servers, switches, and servers and switches all need to use optical modules, optical fiber jumpers or other transmission carriers to achieve data interoperability. The following picture shows the direct connection of 400G QSFP-DD transceivers in the data center.

Metropolitan Bearer Network

Cloud computing, big data, ultra-high-definition video, Internet of Things, VR/AR, 5G, AI, and Internet of Vehicles have created new requirements for bearer networks: ultra-high bandwidth, massive connections, ultra-low latency, and high reliability. During the large-scale 5G commercialization of the metropolitan area network, the core layer bandwidth will be developed to 200GE/400GE since traditional 100GE ports fail to accommodate the requirements of 5G aggregation and core layer for ultra-broadband. Therefore, the optical interconnection solution based on 400G becomes an inevitable choice.

Long-Distance High-Capacity Transmission

Long-distance transmission is in high demand for the market as new services continue to emerge in an endless stream, raising the requirements for the transmission network bandwidth. Also, intercom operators put up higher standards for network management and modulation flexibility. All of these aspects support the 400G application in long-distance transmission because it can use a single 400G wavelength to operate 400G ports, modify the wavelength path in accordance with organizational needs, achieve direct wavelength access in the optical path, and reduce latency and power consumption.

FAQs about 400G QSFP-DD Transceivers

Q: Can I have an OSFP on one end of a 400G link, and a QSFP-DD on the other end?

A: Yes. The OSFP and QSFP-DD describe the physical form factor of the module. As long as the Ethernet media types are the same (i.e. both ends of the link are 400G-DR4, or 400G-FR4, etc.), OSFP and QSFP-DD modules will interop with each other.

Q: Can I plug a QSFP-DD transceiver module into an OSFP port?

A: No. QSFP-DD and OSFP are absolutely different form factors. You can use only one kind of form factor in the corresponding system. If you have an OSFP system, then 400G OSFP optics must be used. If you have a QSFP-DD system, then 400G QSFP-DD transceivers must be used.

Q: What is the difference between 40/100G optical modules and 400G optical modules?

A: Compared with 40G/100G optical modules, the 400G transceivers are making the traditional single-carrier modulation coherent detection of low-end optical modules convert to polarization-multiplexed multi-carrier applications. Besides, 400G optical modules have more packaging form factors and higher network deployment costs with the advantages of low power consumption, great-bandwidth, and high speed.

Q: What does it mean when an electrical or optical channel is NRZ or PAM-4?

A: NRZ stands for "Non-Return to Zero" modulation, and describes an electrical or optical data channel where there are only two allowed amplitude levels, with one amplitude level representing a digital "1" and the other level representing a digital "0". This is the predominant modulation scheme for transmitting data up to 25Gb/s. And PAM-4 stands for Pulse Amplitude Modulation-4, where "4" refers to the number of different amplitude levels of the electrical or optical signal carrying the digital data. In this case, each amplitude level represents two bits of digital data. This enables a PAM-4 waveform to transmit twice as many bits as a NRZ waveform at the same symbol (or "toggle") rate, which means the PAM4 can enable higher bit rates at half the baud rate.

Q: What are the pros and cons of using OSFPs or QSFP-DDs?

A: The QSFP-DD form factor is based on the QSFP form factor with an extra row of electrical pins added. It allows strict backward compatibility with 40G and 100G QSFP modules and is compatible with QSFP 28 modules. However, the OSFP form factor is not compatible with certain existing photoelectric interface, which needs to use adapter to achieve interoperability. On the other hand, to dissipate the larger power of 400G modules, the QSFP-DD relies on an external heatsink that is part of the switch platform. But OSFP's heatsink is integrated into the module case itself and it has larger surface area than QSFP-DD, which ensures the best possible thermal contact between the power dissipating components and the heatsink, and contributes to better thermal performance.

400G QSFP-DD Transceiver Future and Trends

The technical advancement of 400G improves the efficiency and capacity of data transmission and brings a better network experience for users. With the merits of high bandwidth, low latency, and low power consumption, the 400G QSFP-DD module might be the ideal choice for next-generation wireless networks and ultra-large-scale data centers.

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NRZ Vs. PAM4 Modulation Techniques | FS Community