Why is a point-to-point connection also considered a collision domain (according to Cisco)?

Question

A point-to-point is considered a broadcast and a collision domain.

Answer 1

Point-to-point does not mean it's not a shared media.  Look at frame-relay, you have PVC, which are point-to-point links, but the media (frame-relay cloud) is a shared media and hence, a collision domain.

Answer 2

Point-to-point links are still considered a network. Routers separate networks but still follow the same rules. Any portion of a network must still follow CSMA/CD (CA). Is a single PC to a Router connection considered a network?

Most likely a collision will not happen between a point-to-point at full duplex but, its good practice to think of it as a separate network within a broadcast and collision domain.

Ref: http://www.cisco.com/en/US/docs/internet...