In cutting through the clutter of the various Ethernet interfaces, it is as important to know what to ignore as it is what to pay attention to. This slide looks at “Bob Smith” termination schemes which are networks of resistors and capacitors deployed on the cable side of the Ethernet coupling transformers. These are extremely common in Ethernet interface designs primarily because they are very effective at reducing the emission and reception of common-mode noise on the Ethernet cables. The key take-away here is that these termination networks, while effective and common, are in no way protection circuits. When they are seen, do not assume protection is not needed.