Cable Provider Phone Service vs. VoIP vs. Copper POTS

[Protel8000]

I have Comcast for Internet, and they offer phone service "Xfinity Voice" however it is not compatible with a regular ATA - you have to use a special cable modem with a built in RJ-11 port. Does anyone know the technical side of what makes a cable provider's voice service different than standard VoIP? Does it use different compression or transmission technology than VoIP... and if so, does it work closer to traditional copper lines as far as for data transfer like fax or dial up data connections?

[Protel8000]

Here's an article with a little more information: https://classroom.synonym.com/comcast-voip-15708.html

Not as technical as I would like to see, but it does answer some of this: Yes it is VoIP, but  it's routed on a "private" internal network instead of over the Internet, and can have reserved bandwidth and such as a result.

[dc4code]

Typically VoIP from your ISP can be very good since they own the network they can make the Voice quality very decent but that's not always the case.

Although my Spectrum Line uses G722 HD Voice It works very VERY nicely.. It even works with Dial-up and FAXes. but they might just be my experience. It's up to you to try it.