What Is QSFP28 100G CWDM4 and How Does Facebook Data Center Apply It?

QSFP28 100G CWDM4 module is designed for use in 100GBASE Ethernet throughput up to 2km over single-mode fiber (SMF). This article will focus on the working principle, specification, and a Facebook Data Center application case to make you have a full understanding of the QSFP28 100G CWDM4 optical transceiver.

What is QSFP28 100G CWDM4 and How It Works

The QSFP28 100G CWDM4 transceiver is designed for use in 100 Gigabit Ethernet (GbE) links on up to 2km over duplex single-mode fiber (SMF). The 100 Gigabit Ethernet signal is carried over four wavelengths. Multiplexing and demultiplexing of the four wavelengths are managed within the device.

100G CWDM4 module adopts CWDM MUX/DEMUX technology with four central wavelengths of the lanes at 1271, 1291, 1311, and 1331nm. On the transmission side, 100G CWDM4 module converts 4 electrical input channels into 4 lanes with optical signal and multiplexes them into a single channel of 100Gbps optical transmission, reversely, the module optically demultiplexes 100Gbps input into 4 lanes signals and converts them to 4 lanes of electrical data on the receiver side.

Figure 1: QSFP28 CWDM4 100G module working principle

QSFPTEK QSFP28 100G CWDM4 Specification

Table 1 - QSFPTEK QSFP28 CWDM4 100G Spec

Case Analysis: How is QSFP28 100G CWDM4 Applied in Facebook Data Center？

To increase the switch interconnect bandwidth of data centers to 100G, Facebook chooses 100G CWDM4 QSFP28 to enable 100G over duplex single-mode fiber (SMF) as a cost-effective way to realize large-scale deployment in 100G data centers.

To enable lower costs and consider the actual data center environment, Facebook has relaxed several specifications including as below:

1. Reducing the operating case temperature from 0-70 ˚ C to 15-55 ˚ C;

2. Reducing the distance requirements from 2km to 500m, based on that, the link loss budget was reduced from 5dB to 3.5dB.

The relaxed specification ensures that optical transceivers will interoperate with the standard MSA version of the specification over distances shorter than 500 meters.

Table 2 - CWDM4 MSA Spec vs. FB Relaxed Spec

To ensure that the transceivers would perform reliably once installed, Facebook tested at the component level and system lever.

The component level tests were performed at 25.78Gb/s per channel to characterize both transmitter (average optical power, extinction ratio, jitter, OMA, etc.) and receiver (sensitivity) performance over different temperatures and different fiber lengths as shown in fig. 2 and fig. 3.

Fig. 2 - QSFP28 CWDM4 100G component eye diagram validation data

Fig. 3 - QSFP28 CWDM4 100G component OMA validation data

After component tests, the system level traffic tests were performed at their switch platforms. Fig. 4 shows 100Gbps Ethernet traffic running through 32 concatenated CWDM4 ports without packet loss. 

Fig. 4 - QSFP28 CWDM4 100G system level test structure

Case Conclusion

This Facebook case proves that the 100G CWDM4 is an effective technology for increasing the switch interconnect bandwidth of data centers. Facebook introduces a way of relaxing the transceiver performance specifications (temperature, reach) to meet our data center operating requirements. This 10G CWDM4 technology solution provides referential and can be deployed at scale to support our actual production application traffic throughout our data centers.

QSFPTEK has been focusing on the R&D and production of high-speed optical interconnect products for 10 years. QSFP28 100G CWDM4 modules are available at the best price. Contact QSFPTEK and get a quote.