Huawei releases Wi-Fi 6 router "HUAWEI WiFi AX3 NEW" compatible with IPoE IPv6 at 8,000 yen levelMSI Exhibits Wi-Fi 6E Gaming Wi-Fi Router at TGS 2022Regarding Ethernet or 10GBASE-T, since 2017 [10GBASE-T, finally popular?], we delivered all 11 episodes and 2 extra episodes.However, twisted pair copper wiring Ethernet is up to 10GBASE-T, and 25/40GBASE-T has not yet been put into practical use.MII, formally Media Independent Interface, was actually defined by 100Mbps Ethernet "IEEE 802.3u".Ethernet up to 10 Mbps has a structure (below left) in which the data link layer and physical layer are connected by an interface called "AUI (Attachment Unit Interface)".This AUI is a system consisting of 6 signal lines and a power supply (12V) as shown on the left, and is mainly targeted at "10BASE5".With 10BASE2 and 10BASE-T, except for early products, it was possible to mount a transceiver on a network card without pulling out a cable, so the use of an AUI cable was extremely rare (10BASE2 aside, I have never seen a product that uses AUI with 10BASE-T).However, although AUI is physically invisible, it seems that AUI was still used inside 10BASE5 and 10BASE-T.Now, with 100BASE-X, the direction of supporting multiple physical media has come into view.As explained in Part 3 of this series, "History and Development of Optical Ethernet," 100BASE-FX and 100BASE-TX were standardized in IEEE 802.3u, and 100BASE-LX10 and 100BASE-BX10 were standardized in "IEEE 802.3ah."The interface is configured as shown in the red frame in the left figure.There are 16 signal lines alone, and there are actually +5V lines and MDIO (Management Data Input/Output) signal lines, so 20 signal lines are required even if GND is removed.Partly because of this, a 40-pin MII connector was defined.However, there was a strong demand for the use of optical transceivers called SFP (Small Form-factor Pluggable), especially for applications that use optical fibers.Since the days before the advent of optical Ethernet, optical devices have been provided in the form of optical/electrical conversion modules instead of being directly mounted on network cards, and there has been a need for optical Ethernet to follow suit.As a result, the configuration shown in the figure below has become common for optical Ethernet.The specification of this optical module is the former SFF (Small Form Factor) Committee, and now the SFP (Small Form Factor Pluggable) Transceiver of "INF-8074i" specified by "SNIA (Storage Networking Industry Association)" is used. became.For example, the 100BASE-FX module handled by FS is an example of an actual product.The size is very compact with a total length of 45 mm, width of 13.7 mm, and height of 8.6 mm, and it is possible to install two ordinary PCI or PCI Express cards if you like.By using this, the optical Ethernet card itself can be shared and the modules to be installed can be replaced, making it possible to switch between 100BASE-FX/LX10/BX10.Therefore, a specification called "RMMI (Reduced MII)" was formulated to reduce MII signals.By the way, MII itself supports 10Mbps (10BASE-T) in addition to 100Mbps.This specification was announced in 1998 as the "RMMI Specification" by the RMII Consortium formed in 1997 by six companies: 3Com, AMD, Bay Networks, Broadcom, National Semiconductor, and Texas Instruments.Therefore, even 1 Gbps is defined as equivalent to MII, and is called "GMII (Gigabit MII)".Although the transfer speed has become 10 times faster, the data width has been expanded to 8 bits, perhaps thinking that it would be unreasonable to increase the speed of the signal to 10 times as it is.In other words, 5 times the signal speed x 2 times the data width is a calculation of 10 times the transfer speed.Strictly speaking, in the case of RMII, only the rising edge of the 50MHz clock signal triggers 50MHz x 2bit = 100Mbps, whereas in GMII, data is sent on both the rising and falling edges (so-called DDR: Double Data Rate) achieves 125MHz x 4bit x 2 = 1000Mbps even though the reference clock itself is 125MHz.Although it is Cisco's own standard, Cisco has shipped many SGMII-compatible modules, and in response to this, various vendors have launched SGMII-compatible standards, and as a result, it has become a de facto industry standard.It is a standard for serial transfer of 1000 Mbps with 8b/10b encoding, with a signal speed of 1.25 Gbps and a bus width of 1 bit (Differencial, so the number of pins is 2).Unlike RMII/RGMII, this is a replacement for the existing MII/GMII, but as I touched on in Part 4, originally 1000BASE-X internally handled 1.25 Gbps using 8B10B encoding. Therefore, it can be considered that it was just released outside as it is, and the fact that it saves extra work and is just right (the overhead of converting to GMII can be saved) may also be a factor in its popularity.Freelance technical writer.His expertise spans a wide range of fields, from CPUs, memories, and chipsets to communications, OS, databases, and medical-related fields.Homepage is http://www.yusuke-ohara.com/Copyright ©2018 Impress Corporation.