How Many 400G Transceiver Types Are in the Market?

With the tremendous requirement for high bandwidth in 5G, loT and cloud data center, the focus of 400G Ethernet has been lasting for a couple of years. Vendors such as Cisco, Arista, and juniper are developing and testing technologies for 400G Ethernet networks. As the key hardware devices for interconnecting optical networks and providing a robust 400G solution for data centers, there is no dispute that 400G transceivers, also known as 400G data center transceivers, will become the mainstream of the industry.

Transceiver Application

According to the transceiver application, optical modules can be classified into two categories: client-side transceivers and line-side transceivers.

400G Ethernet Transceivers for Client Side Transmission

Client-side transceivers are used to interconnect between the metro networks and the optical backbone. The term "client side" refers to relatively short distances compared with the line side, generally from 50m to 10km and with only one transceiver connected to fiber thus no coherent optics is needed. There are various transceiver interfaces that have been standardized by IEEE and MSA. Most importantly, it has an agreed and standardized interface that is used for the network connection. PAM4 has been chosen by IEEE 802.3bs for 400GE client side transmission.

400G Coherent Transceivers for Line Side Transmission

Different from client side, line side reaches transmission distances of 80km or even longer using DWDM. Coherent technology is expected to implement 400G line side transmission. OIF has been working on standardizing the 400G coherent DWDM interface for DCI and other metro/access applications. The signal processing of coherent transport is much greater than that of short reach PAM4 data center transmission, which requires more DSPs and power than in client side transmission.

Interface Standard

The transceiver interfaces are defined by the interface standards. The following chart lists the common 400G Ethernet standards and the corresponding interfaces.

Interface standard	Interface	Link Distance	Media Type	Optical Architecture
IEEE 802.3bs	400GBASE-SR16	100m	MMF	16× 25G NRZ 850nm
	400GBASE-DR4	500m	SMF	4× 100G PAM4 1300nm
	400GBASE-FR8	2km	SMF	8× 50G PAM4 WDM
	400GBASE-LR8	10km	SMF	8× 50G PAM4 WDM
IEEE P802.3cm	400GBASE-SR8	100m	MMF	8× 50G PAM4 850nm
	400GBASE-SR4.2	100m	MMF	8× 50G PAM4 BiDi 850/910nm
IEEE P802.3cn	400GBASE-ER8	40km	SMF	8× 50G PAM4 WDM
IEEE P802.3ct	400GBASE-ZR	80km	SMF	Coherent DWDM
100G Lambda MSA	400GBASE-FR4	2km	SMF	4× 100G PAM4 CWDM
	400GBASE-LR4	10km	SMF	4× 100G PAM4 CWDM
CWDM8 MSA	400G-CWDM8-2	2m to 2km	SMF	8× 50G CWDM
	400G-CWDM8-10	2m to 10km	SMF	8× 50G CWDM

Note: 400GBASE-SR16 has not been released by any transceiver vendors. As 400GBASE-SR16 interface requires a high fiber count (32 fibers per duplex link), this standard is not expected to enter the 400G transceiver market.

400G Transceiver Form Factor

There are several mainstream 400G form factors，400G QSFP-DD, OSFP, CFP8, COBO, etc., some of which have been put in the market and some are still as a design.

CFP8 is the first generation 400G transceiver, with a relatively large physical size, offering the lowest port density.

COBO is named for Consortium for On-Board Optics, installed internally to the line-card equipment in a controlled environment, thus lacking flexibility.

OSFP stands for Octal Small Form Factor Pluggable, which is a new kind of pluggable form factor. There are some companies that have already sold 400G OSFP transceivers on the website.

400G QSFP-DD transceivers

are now one of the most popular optical modules in the market, which have been launched and manufactured by Finisar, Innolight,

FS.com

, etc.

The table below includes detailed comparisons of size, compatibility, power, etc. for the three main form factors: OSFP, QSFP-DD and CFP8.

	OSFP	QSFP-DD	CFP8
Application Scenario	Data center & telecom	Data center	Telecom
Size	22.58mm× 107.8mm× 13mm	18.35mm× 89.4mm× 8.5mm	40mm× 102mm× 9.5mm
Max Power Consumption	14W	14W	24W
Backward Compatibility with QSFP28	Through adapter	Yes	No
Electrical signaling (Gbps)	8× 50G	8× 50G	8× 50G
Switch Port Density (1RU)	36	36	16
Media Type	MMF & SMF	MMF & SMF	MMF & SMF
Hot Pluggable	Yes	Yes	Yes
Thermal Management	Direct	Indirect	Indirect
Support 800G	Yes	No	No

Among these three transceiver form factors, it is obvious CFP8 lacks density, unlike the other two 400G transceivers. OSFP modules have been designed with 800G in mind. The QSFP-DD form factor has the main advantages of its high density, small size, and back forward compatibility that it supports QSFP28 enabling easier migration to 400G Ethernet, which addresses the industry need for high speed and high-density networking. Therefore it is expected that QSFP-DD form factor will become the most appropriate form factor for the 400G Ethernet applications.

Summary

Apart from the above categories of 400G transceivers, fiber mode, wavelength, etc. are also the common characteristics that are used in optical transceiver classification, which are not further explained. The demand for high-speed data transmission is rocketing. As the transceiver market is pushed to shift, we can expect the 400G Ethernet deployment in the next-generation data centers and the popularity of 400G optical modules in the near future. Though both opportunities and challenges in the 400G transceiver test exist in the research stage, 400G Ethernet is still an inevitable trend.