Tag: Ethernet

With Fast Ethernet, Ethernet introduced something new. Previously, the Physical Signaling layer was integrated into the MAC and connected to the actual media through a Media Attachment Unit. While the user could switch between twisted pair (10Base-T), thinnet (10Base2), thicknet (10Base5), or even fiber (10Base-F) simply by changing MAUs, switching to a different encoding (e.g. Fast Ethernet) would require a completely new interface.

Instead of requiring new networking equipment to manage the PCS of each individual protocol, the MAC communicates with the PHY with a Media Independent Interface (MII). Now, free of protocol-specific encodings, different line rates and protocols could be selected by simply switching between different PHYs, leaving the MAC unaffected. While interchangeable PHYs is now the domain of high-end networking (e.g. SFP modules), the MII interface and its derivatives are the primary mechanism for connecting integrated MACs (and FPGAs) to commodity Ethernet transceivers.

Much of my recent professional development has focused on Ethernet, making it a convenient target for technical essays. Unlike much of the Internet, this series of essays will focus on practical implementation of Ethernet from an FPGA or ASIC perspective. This means the necessary waveforms and encodings to generate ethernet packets when directly connected to a PHY or medium.

The essays will be making extensive references to IEEE 802.3-2022 and every effort will be made to specify the exact clauses for further research by the reader. I will not be using the amendment names (e.g. 802.3z for Gigabit Ethernet) because they are not not useful for finding content within the actual standard and any given clause may have been modified by multiple amendments.