Recent years have seen the evolution towards the Internet of Things (IoT) and the explosion of cloud computing and 5G, raising large pressure on data centers to ramp up both network capacity to 400G and driving cloud service providers and data centers to search for new solutions to achieve their 400G Data Center Interconnects (DCIs). 400G QSFP DD is becoming one of the most popular cutting edge 400G DCI solutions. Why choose QSFP-DD over other form factors like OSFP, CFP8, or even COBO? And how to utilize it for 400G DCI applications. Read more to find out.
Basically, there are mainly four form factors that are applied in 400G DCI, which are QSFP DD, OSFP, CFP8, and COBO. In this part, we will figure out how QSFP DD outperforms the others. First, let's take a deep look at 400G QSFP DD itself.
QSFP-DD (also called QSFP56-DD) stands for Quad Small Form Factor Pluggable Double Density. It has doubled interfaces than which QSFP28 has. QSFP-DD is IEEE802.3bs and MSA standard compliant. With high-level PAM4 modulation technology, it can deliver a 400G (8x 50G or 4x 100G) signal with minimized power consumption, which makes it qualified to create a cost-effective way to scale to 400G for data centers at the same time reducing per port hardware costs.
Figure 1: 400G QSFP-DD DR4 Module
Compared to the other 400G form factors like OSFP, CFP8, and COBO, 400G QSFP-DD is of great benefits when applied for data center interconnects, including:
Being backwards compatible with QSFP+, QSFP28, and QSFP56 makes it much easier to upgrade to 400G networks.
Supported by PAM4 modulation, QSFP DD is a more cost-effective solution for 400G DCI with ultra-low power consumption.
400G QSFP DD provides more flexibility and scalablibity since it has more lanes (8 or 4 lanes) than other form factors.
For more detailed information about the differences between these form factors, please check this article for reference: Differences Between QSFP-DD and QSFP+ / QSFP28 / QSFP56 / OSFP / CFP8 / COBO.
The network architecture of the Next-Generation 400G Data Center is generally pided into three layers, namely, Spine Core, Edge Core, and ToR (Top of Rack). There are various 400G QSFP-DD equipment for data center interconnects of different transmission distances.
Figure 2: Architecture of 400G DCI
Transmission Distance < 5m
The transmission distance between ToR access switches and server NICs is generally less than 5m. In this case, 400G QSFP-DD DACs would be a better option. It primarily enables high-bandwidth 400G links and provides a QSFP-DD-to-QSFP-DD copper direct-attach solution when QSFP DD modules are adopted in 400G DCI. They are suitable for very short links and offer a cost-effective way to establish a 400-Gigabit link between QSFP-400G ports of switches/routers within racks and across adjacent racks.
Transmission Distance < 100m
For the transmission between ToR access switches and Edge Core switches, which is generally less than 100m, 400G QSFP-DD AOC with 8x 50G PAM4 modulation technology is more often used with its advantages of lower weight, longer transmission distance, and easier installation and maintenance.
Transmission Distance < 2km
The transmission distance between Edge Core switches and Spine Core switches is generally less than 2km, for which 400G QSFP-DD FR4 optical transceiver featuring low-power, high-density and high-speed would be a great option.
Transmission Distance < 100km
The transmission between Spine Core and Core Router belongs to DCI Metro Interconnect where the transmission distance is generally less than 100km. 400G QSFP DD LR8 transceivers can achieve high-speed transmission with PAM4 technology for the interconnect between Spine Core and Core Router.
Except for the products mentioned above, FS has a full range of 400G QSFP DD transceivers, 400G DACs, as well as QSFP-DD breakout cables for 400G DCI applications with guaranteed quality and worry-free services. The following are three product lists for reference.
|Modules||Max. Data Rate||Form Factor||Wavelength||Max. Distance|
|400G QSFP-DD SR8||400Gbps||QSFP-DD||850nm||100m|
|400G QSFP-DD DR4||425Gbps||QSFP-DD||1310nm||500m|
|400G QSFP-DD XDR4||400Gbps||QSFP-DD||1310nm||2km|
|400G QSFP-DD LR4||400Gbps||QSFP-DD||1271nm,1291nm,1311nm,1331nm||10km|
|400G QSFP-DD LR||400Gbps||QSFP-DD||1310nm||10km|
|400G QSFP-DD ER8||425Gbps||QSFP-DD||1310nm||40km|
|Modules||Max. Data Rate||Form Factor 1||Form Factor 2||Cable Length|
|0.5m (2ft) 400G QSFP-DD DAC||400Gbps||QSFP-DD||QSFP-DD||0.5m|
|1m (3ft) 400G QSFP-DD DAC||400Gbps||QSFP-DD||QSFP-DD||1m|
|1.5m (5ft) 400G QSFP-DD DAC||400Gbps||QSFP-DD||QSFP-DD||1.5m|
|2m (7ft) 400G QSFP-DD DAC||400Gbps||QSFP-DD||QSFP-DD||2m|
|2.5m (8ft) 400G QSFP-DD DAC||400Gbps||QSFP-DD||QSFP-DD||2.5m|
|3m (10ft) 400G QSFP-DD DAC||400Gbps||QSFP-DD||QSFP-DD||QSFP-DD|
|Module||Max. Data Rate||Form Factor 1||Form Factor 2||Cable Length|
|400G QSFP-DD to 4x100G QSFP56||400Gbps||QSFP-DD||4 QSFP56||0.5m (2ft)|
|CAB-D-8S-400G-1M||400Gbps||QSFP-DD||8 SFP56||1m (3ft)|
|CAB-D-2Q-400G-1M||400Gbps||QSFP-DD||2 QSFP56||1m (3ft)|
|400G QSFP-DD to 4x100G QSFP56||400Gbps||QSFP-DD||4 QSFP56||1m (3ft)|
|400G QSFP-DD to 4 x100G QSFP28||400Gbps||QSFP-DD||4 QSFP28||1m (3ft)|
|400G QSFP-DD to 4x100G QSFP56||400Gbps||QSFP-DD||4 QSFP56||1.5m (5ft)|
|CAB-D-8S-400G-2M||400Gbps||QSFP-DD||8 SFP56||2m (7ft)|
|CAB-D-2Q-400G-2M||400Gbps||QSFP-DD||2 QSFP56||2m (7ft)|
|400G QSFP-DD to 4x100G QSFP56||400Gbps||QSFP-DD||4 QSFP56||2m (7ft)|
|CAB-D-8S-400G-2.5M||400Gbps||QSFP-DD||8 SFP56||2.5m (8ft)|
|CAB-D-2Q-400-2.5M||400Gbps||QSFP-DD||2 QSFP56||2.5m (8ft)|
|400G QSFP-DD to 4x100G QSFP56||400Gbps||QSFP-DD||4 QSFP56||2.5m (8ft)|
|400G QSFP-DD to 4 x100G QSFP28||400Gbps||QSFP-DD||4 QSFP28||3m (10ft)|
|400G QSFP-DD to 4x100G QSFP56||400Gbps||QSFP-DD||4 QSFP56||3m (10ft)|
|400G QSFP-DD to 4 x100G QSFP28||400Gbps||QSFP-DD||4 QSFP28||5m (16ft)|