Hello all, Let's take two products: Hikvision 2CD2132-I Hikvision 2CD2132F-IWS Their product numbers have 3 differences: 1) F 2) W 3) S It appears that they are identical except for three things: 1) Two way Audio 2) Two way Alarm 3) SD Card Slot Can I assume that each letter corresponds to a function? If so, is there a legend somewhere to help me understand at a glance the product numbers/letters and features of each camera? Can I assume the I stands for IP camera? Do all Hikvision IP cameras take either POE or a 12 volt adapter? Are there other camera features that are designated a letter? Is there such a thing as 1 way Audio and or 1 way Alarm? Thanks a lot.