400G SR4 and SR8: Explore the Difference

Date 07/08/2024

This article tells you what 400G SR4 and SR8 are, and lists their differences, advantages and disadvantages to help you make a better choice between the two.

400G SR4 and 400G SR8 are two widely used solutions in the ever-increasing data traffic and demand for high-speed connections. They can not only meet the increasing throughput requirements but also provide a cost-effective solution for short-distance transmission in data centers. In this article, I will introduce the differences between these two optical modules to help you make a choice.

What is 400G SR4

400G SR4 is an optical module for short-distance high-bandwidth data transmission, supporting a 400Gbps rate. It receives and transmits data by using 4 channels, each of which supports 100Gbps rate. The technology uses MMF fiber jumpers for transmission, usually OM4, to support short-distance transmission. Its interface is MTP/MPO connector, containing 12 or 16 optical fibers.

400G SR4 Transceiver from QSFPTEK

QSFPTEK provides OSFP 400G SR4 form factor optical modules, supporting 400Gbps high-speed transmission, low power consumption, and high-density connection, which is ideal for high-performance computing and AI data centers. It is compatible with mainstream 400G/100G facilities, ensuring seamless upgrades and providing stable and reliable transmission performance.

OSFP 400G SR4 can be connected to two OSFP56 200G SR4 optical modules via breakout fiber.

OSFP 400G SR4 product data sheet:

	OSFP-400G-SR4	OSFP-400G-SR4 InfiniBand
Wavelength	850nm
Connector	MTP/MPO-12
Distance	50M
Modulation	4x 106.25G PAM4
Power Consumption	≤9W
Transmitter Type	VCSEL
Application	400G to 4x100G Breakout Data Center	InfiniBand 400G to 4x100G Breakout

What is 400G SR8

400G SR8 is another high-speed optical module designed for data centers that support short-distance high-bandwidth data transmission. Unlike SR4, it uses 8 channels for parallel data transmission, and the transmission rate of each channel is 50Gbps. SR8 can achieve a 100M transmission distance through OM4 MMF fiber, and its interface is usually 24-fiber MPO and MPO-16.

400G SR8 Transceiver from QSFPTEK

QSFPTEK provides optical modules in QSFP-DD, QSFP-DD 56, and OSFP packages, which are compatible with mainstream brand switches on the market. 400G SR4 provides a flexible fiber reorganization function and can be configured with 50G, 100G and 200G. For example, it can be split into 8x 50G SR. This upgrade mode enables it to use existing fiber infrastructure for network upgrades, which is an economical solution.

400G SR8 package parameter table:

	OSFP-SR8-400G	QSFP-DD-SR8-400G	QSFP56-DD-SR8-400G
Wavelength	850nm
Connector	MTP/MPO-16
Distance	100m	70m (over OM3) 100m (over OM4)	70m (over OM3) 100m (over OM4)
Modulation	PAM4
Power Consumption	≤12W
Transmitter Type	VCSEL
Application	400G to 8x50G Breakout Data Center	400G to 8x50G Breakout Data Center	400G to 8x50G Breakout Data Center

Difference Between 400G SR4 and SR8

If you are considering 400G SR4 and 400G SR8, you need to consider the following factors and make a choice:

	400G SR4	400G SR8
Optical Channels Count	Uses 4 channels, each supporting 100Gbps	Uses 8 channels, each supporting 50Gbps
Fiber Count	4 transmit and 4 receive, total of 8 fibers	8 transmit and 8 receive, total of 16 fibers
Connector	MTP/MPO-12	MTP/MPO-16
Distance	100M with OM4 MMF	70M with OM3 100M with OM4
Applications	Suitable for short-distance transmission within data centers, supporting connection with 100G modules	Similar to SR4 applications, but can support use with OM3 MMF and can be connected with 50G modules
Cost	SR4 uses fewer fibers, which can reduce overall costs	SR8 needs to deploy more fiber to support its flexibility

Pros and Cons

Below are the pros and cons of 400G SR4 and SR8, which can also help you make the final decision.

	400G SR4	400G SR8
Pros	The rate of each channel reaches 100Gbps	The lane granularity is larger than SR4
	Fewer channels mean lower power consumption	8 channels provide greater flexibility in certain scenarios
	Fewer channels ensure a simple wiring structure	The channel rate is only 50Gbps, and the heat generation is lower
	For data centers that have already deployed 100G networks, 400G SR4 can be deployed based on existing infrastructure	It consists of 8 50Gbps channels, which is less technically difficult and less expensive than SR4
Cons	Low port scalability	8 channels increase the complexity of the wiring structure
Cons	The higher the channel rate, the more likely it is to heat up.	Since there are 8 channels, its power consumption is increased

From the comparison in the table, we can see that 400G SR4 has 4 channels, simpler wiring, and uses optical fiber with MTP/MPO-12 connectors for transmission, up to 100M. It is suitable for short-distance high-performance transmission in high-speed data centers and supports 400G to 4x 100G breakout applications. Fewer channels also mean lower power consumption and lower scalability than SR8.

400G SR8 has 8 channels, each with a rate of 50Gbps. It uses optical fiber with MTP/MPO-16 connectors for transmission, and the maximum transmission distance using OM4 MMF is up to 100M. Similar to the applicable scenarios of SR4, both are suitable for high-performance transmission. It can be divided into 400G to 2x 200G SR4 or 400G to 8x 50G breakout applications, which has higher flexibility than SR4, but its wiring is also more complicated.

Conclusion

Both 400G SR4 and SR8 provide short-distance high-speed solutions for today's high-speed data centers, but choosing between them depends on your data center infrastructure and your application requirements. If you have cabling complexity requirements, SR4, which requires fewer fibers, is undoubtedly a better choice. If you need higher flexibility, then SR8 meets your requirements. If you have any questions about 400G SR4 and SR8, please feel free to contact QSFPTEK's CCIE/HCIE engineers at support@qsfptek.com.