Application of 100G QSFP28 Interface Model For Data Centers

After years of development, 100G applications have formed a variety of technology types and alliances, whether it is the standardized ieee802.3bm or the 100G application model launched by SWDM, MSA and other organizations. There are many kinds of interfaces and application technologies supporting 100G, and each has its own characteristics.

For the practical application of the data center, the distance between the connection points of most data centers does not exceed 500 meters. From a large number of 100G interface models, we have selected four types that are most likely to be used in data centers for further analysis for users who need to deploy 100G for reference.

1. 100GBase-SR4

100GBase-SR4 complies with the new standard ieee802.3bm issued in 2015. It uses 4 channels composed of 8-core multimode fiber for parallel transmission. Both multimode OM3 and OM4 optical fibers support 100G applications. The interface adopts 12 core MPO interface. The middle four core optical fiber does not need to be used. Each channel supports 25G. The transmission model is completely consistent with 100GBase-SR4 in ieee802.3ba. The optical transceiver adopts 100G QSFP28 SR4. This model can use conventional OM3 and OM4 multimode optical fibers to support 70m and 100m distances of 100G applications respectively.

2. 100GBase-SWDM4

SWDM (Short Wavelength Division Multiplexing) transmits four wavelength bands of optical signals over a single core of multimode fiber. The principle of WDM is similar to CWDM on single-mode, but SWDM is the first application of WDM technology on the short wavelength band of multimode fiber. It can be referred to the transmission principle model in the following figure:

The main transmission window of traditional OM3 and OM4 multimode fiber is defined at 850nm. If SWDM technology is adopted, four windows are required to transmit optical signals, and the four wavebands still use VCSEL vertical cavity surface emitting lasers with high cost performance. In order to improve the overall bandwidth, the bandwidth of the new generation multimode fiber WBMMF(Wideband Multimode Fiber) is increased. In WBMMF, the highest bandwidth performance is around 880nm band, and the highest bandwidth point is higher than that of traditional OM4 multimode fiber. The SWDM technology can also use OM4 optical fiber as the transmission medium, but the transmission distance should be reduced accordingly. Compared with the SR4 model, SWDM4 requires only 25% of the optical fiber.

3. 100GBase-PSM4

100GBase-PSM4 adopts single-mode optical fiber parallel transmission mode. Each 100G model adopts 8-core single-mode optical fiber to form four independent channels. The interface adopts 12 core MPO interface, in which the middle 4-core optical fiber of MPO interface is not enabled, and each channel supports 25G. The optical fiber transmission model is similar to 100GBase-SR4. The biggest difference is that PSM4 adopts single-mode optical fiber as the transmission medium and laser light source 1310 window. The optical transceiver also adopts QSFP28, and the connector adopts MTP / MPO single-mode APC. At present, 100GBase PSM4 has not been recognized by IEEE standardization organization, and is mainly promoted by PSM4 MSA alliance.

4. 100GBase-CWDM4

 100GBase-CWDM4 is a 100G transmission model based on single-mode coarse wavelength division multiplexing(CWDM) technology. The fiber optic transceiver uses a single-mode laser light source with LC duplex interface, and supports four long wavelength bands of signal transmission on each core fiber, these four emission windows are 1271nm,1291nm,1311nm,1331nm, and each band transmits 25G. 100GBase-CWDM4 model is also used QSFP28 optical transceiver.Compare to traditional single-mode 10KM transceiver with high cost, the 2KM QSFP28 100G CWDM4 transceiver has a competitive price.

5. Summary

 Different types of data centers determine different needs. Not all data center users currently have the need to deploy 100G, so what types of users need to deploy 100G networks the most? To answer this question, we can divide data centers into two major categories, IDC (Internet Data Center) and EDC (Enterprise Data Center). Relatively speaking, some IDC data centers have more urgency to deploy 100G backbone networks, such as the data centers of large interconnection companies or carriers or some scaled cloud computing data centers.

In terms of current price, although the wiring cost of multi-mode 100G based on SR4 is relatively high, the overall price has certain advantages, especially the price of SR4 optical transceiver is significantly lower than that of other types. Meanwhile, the price of optical transceiver based on CWDM single-mode is significantly higher than that of the other three types. The overall price difference between PSM4 and SWDM is small. As the SWDM alliance participated by a small number of optical transceiver manufacturers, it is not a public technology at present, and the market price remains relatively high temporarily. However, from the perspective of technology and cost composition, there is still a large room for price decline of SWDM, and this product has a certain market potential in the future.