400G Ethernet standard Introducition 2022
What is ethernet standard
The prototype topology of Ethernet was proposed by Xerox in 1973 and realized in the laboratory, with a speed of only 2.94Mbps. In 1980, Xerox and DEC, Intel jointly published the first version of the 10Mbps Ethernet standard DIX V1, the famous Blue Book. In 1982, DIX V2 was officially announced. On this basis, the Institute of Electrical and Electronics Engineers (IEEE) introduced the Ethernet standard IEEE802.3, marking the standardization of Ethernet. In addition to supporting a transmission rate of 10Mpbs baseband and a node transmission distance of 500m, the standard adopts the carrier sense multiple access (CSMA/CD) access control method with collision detection to ensure orderly and efficient transmission services for multiple nodes.
Development of the Ethernet Standard
To meet the ultra-high demand for processors and I/O bandwidth from emerging applications such as hyperscale data centers, cloud providers, and artificial intelligence, high-performance computing, etc., IEEE officially released the 802.3bs standard in December 2017, supporting 200GBASE- R and 400GBASE-R interface types with a maximum rate of 400Gb/s, 4 times the 2010 standard. Further, in 2018, IEEE launched the 802.3cd standard  on the basis of 40GBASE-R, that is, the 50GBASE-R interface type, which helps to achieve 400GbE single-channel high-speed and low port density. At the same time, the single-channel high speed also promotes the application and technical evolution of 200GbE/400GbE.
At present, the 400GbE standard IEEE802.3bs has become the mainstream communication protocol standard at this stage. The standard inherits the CSMA/CD access scheme and physical layer transmission characteristics of the 100G standard IEEE 802.3ba. Its main features include: only supporting full duplex mode, maintaining 802.3 Ethernet MAC frame format and maintaining the maximum and minimum frame lengths in the 802.3 standard, using 64B/66B encoding in the 100G standard, and achieving bit error rates of 10-15 and below , supports Ethernet transmission between optical transport networks and Energy Efficient Ethernet (EEE).
Physical Layer Naming Convention
802.3bs is an evolution of the 100G Ethernet standard IEEE 802.3ba, and their physical layer naming convention symbols are basically the same. Figure 1 shows the naming method of the 400G Ethernet physical layer specification, as shown in the figure, where 400G represents the transmission rate, BASE represents the baseband transmission, "a", "b" and "c" represent the physical medium and Transmission distance, physical layer coding method and wavelength (channel) multiplexing number. When "a" is K, C, S, L, and E, it represents physical media such as PCB backplane, twinaxial copper cable, short-distance optical fiber, long-distance optical fiber, and very long-distance optical fiber, respectively. When "b" is R and P, it means that the encoding method adopted by the Ethernet physical layer is 64B/66B and PAM4 source encoding. The number corresponding to "c" represents the multiplexing number, such as: 1 represents single wavelength or serial, which is generally omitted; n represents the multiplexing scheme of n wavelengths (or channels).
100GbE Physical Layer Specification
Table 2-2 lists the mainstream physical layer specifications in the 100GbE standard [4-5]. For example, 100GBASE-CR10 means using 10 pairs of coaxial copper cables, supporting 100Gb/s short-distance information transmission; 100GBASE-SR4 adopts a star structure, supports multimode fiber (850nm) and exceeds 100m, and has 4 pairs of transmission ports and receiving fiber ports , the rate of each transmission path is 25Gb/s, realizing point-to-point communication. 100GBASE-LR4 uses dense wavelength division (DWDM) to extend to at least 10km on single-mode fiber at 1310nm wavelength. On the other hand, 100GBASE-ER4 combines DWDM technology and single-mode fiber transmission, and single-mode fiber transmits more than 4 ultra-long wavelengths (1550nm) in each direction. Under the semiconductor optical amplifier technology (SOA), information transmission of at least 40km can be realized. Both 100GBASE-KR4 and 100GBASE-KP4 use the 4×25 Gb/s interface specification, support backplane transmission, and the backplane channel attenuation is 35dB and 33dB at 12.9GHz and 7GHz, respectively. As can be seen from Table 2-2, except for 100GBASE-KP4, the transmission signals used in the 100G standard are all NRZ signals.
400GbE Physical Layer Specification
The 400GbE physical layer specification is similar to the 100GbE physical layer specification. Table 2-3 shows the characteristics of the five physical layer specifications in the 400GbE standard. Among them, 400GBASE-SR16 still uses NRZ signals, supports 16 pairs of parallel multimode optical fiber transmission ports, and the rate on each transmission path is 26.5625Gb/s , to achieve point-to-point communication over 100m. 400GBASE-DR4 supports PAM4 modulated signal, uses 4 wavelengths of parallel single-mode fiber in the signal transmission direction, the transmission distance of the fiber is at least 500m, and the rate reaches 106.25G/s. 400GBASE-FR8 also supports PAM4 signals, using 8 wavelengths of WDM technology. This physical layer transmits differential signals at 4 times the optical wavelength on each pair of single-mode fibers, with a rate of 53.125Gb/s and a transmission distance of at least 2km. Similar to FR8, 400GBASE-LR8 and 400GBASE-ER8 both use 8-way WDM, support PAM4 signals, and the transmission distance can be extended to 10km and 40km respectively.