Now that I've got most of my cameras installed, I've figured out some of this stuff...But, it was definitely quite a journey I too took according to Murphy's Law.Immediately after opening the cellophane bag (while standing on the ground), the O ring is installed. THEN I relocate to < insert precarious position here> to complete the connection. Most often this is up on a ladder
%$*# Murphy's law....

Every one I've installed already had the network cable terminated... waterproof connector and fixing cover in the IPC cams slip over the connector and the rubber ring has a slit the allows it to wrap around the cable.Don't know how many times I've terminated the end and then see that I forgot to put the damn thing on there. Snip... do it again.
You'd think that I'd learn after the first few.