When it comes to surveillance systems you have two options: Analog (coax) or Digital (IP).
Analog systems records videos to a digital video recorder (DVR) which is then converted to a digital format for viewing capabilities through a monitor or network for remote access. DVR based security systems are a wired system,
Digital systems or IP Cameras record in digital format so conversion is not necessary. The network video recorder (NVR) stores the video footage which can be accessed remotely. NVR security systems can be wired or wireless.
Due to the complexity of replacing the already installed coaxial BNC cables in an analog systems companies have introduced HDOC (High Definition Over Coax). Analog systems are relatively cheaper because the camera itself records in analog and the footage is then converted at the DVR. The cheaper cost of an analog system does have it setbacks with its limitation on quality.
Digital (IP) based surveillance systems costs more at the camera level. Digital systems processes the video at the camera which has an embedded chipset giving you the most advanced quality and feature-rich video analytics. Due the complexity of the digital cameras it is more costly.