By Eric Bogatin, and Mike Resso, originally published in DesignCon 2008 Everything you ever wanted to know about a single differential channel is contained in its 4-Port S-Parameters, except for channel to channel cross talk. By extending a measurement or simulation to the adjacent two differential channels and using 12 ports, even differential channel noise can be included. There are three types of performance information you can get from the more than 400 unique elements in a 12 port measurement: behavioral models from which system simulation can be directly evaluated, characterization information which describe the properties of the channels, and the very beginning of root cause analysis by extracting simple model information. In this full length paper, all the details of channel analysis are reviewed and examples given of eye diagrams, impedance profiles, channel to channel cross talk and mode conversion. Examples are based on a number of backplane architectures currently in production today.