Analogue CCTV
Cameras on a modern analogue CCTV system send their video in the traditional base band format over coax or UTP cabling back to a digital video recorder (DVR). Here, video is digitized and stored on hard drives. Most modern DVRs are a network device, and as such can be accessed remotely from the LAN, or with the proper configuration, from across a WAN or the internet. There are no tapes to change. Video is kept on hard drives, typically on a FIFO basis so there is always a rolling video archive of the past X days (depending upon drive capacity). So, despite the fact that video is being transmitted from the cameras in an analogue format, live and recorded video is still available over the network.

IP CCTV
IP video cameras broadcast their video as a digital stream over an IP network. Like an analogue system, video is recorded on hard drives, but since the video is an IP stream straight from the camera, there is more flexibility as to how and where that video is recorded. The DVR is replaced with an NVR (network video recorder), which in some cases is just software since it doesn't need to convert analogue to digital. Video footage can then be stored on new or existing network RAID drives as directed by the NVR software.