Looking to get a high-level, vendor-neutral overview of UCC. What books/resources would you recommend?

I'm a pre-sales engineer looking to gain a high-level understanding of UCC/Voice, but I'm not really sure how best to proceed here. I know there are a ton of resources out there, but they all seem really low level & vendor specific. Are there any vendor-neutral books/resources that you'd recommend? Some resource that dives into the general principles of designing & operating UCC environments without going too far into the weeds.