IP (Internet Protocol) is the most common type of CCTV system installed today.
All cameras are connected to the NVR (Network Video Recorder) with an Ethernet network cable. This is the same type of cable that is used on computers. This is a PoE (Power Over Ethernet) connection and allows the NVR to supply power to the connected cameras along with sending and receiving data from the cameras. This includes Video, Audio and controling the camera, such as a vari-focal (zoomable) lens or controlling its movement in the case of a PTZ (Pan, Tilt, Zoom) camera.
IP cameras come in multiple styles/types (see here) and Resolutions. The resolution can be determined by the MP (Mega Pixel) of the camera. The higher the MP the higher the image quality and detail will be of the camera. However, with a higher resolution camera the more storage a camera will require for the same amount of recorded footage, when compared to a lower resolution camera.
Currently IP cameras are available from 1MP all the way to 32MP. With the most common currently being 6MP and 8MP (4K). These both offer great resolution and image detail without using an excessive amount storage on the recorder.
If cameras are required on a shed or remote building away from where the NVR is installed a single ethernet cable or Wireless Link can be installed to this location. Allow multiple cameras to be installed and connected back to the main building and accesible and recorded by the NVR.
Analogue CCTV systems are an older style of system and generally will not be used in new installations. However if a premises already has an Analogue system and cables installed then installing a new recorder and cameras can be a big jump in image quality and saves on removing and replacing the existing cabling.
Analogue cameras generally require multiple cables run to each camera. One a Coax (video) cable and one to power the camera. Power is supplied from an external power supply separate from the DVR (Digital Video Recorder).
HD (High Definition) Analogue cameras are currently available from 2MP up to 8MP. These will generally offer a big upgrade when compared to an older Analogue sytsem.
If you have an older Analogue system the cameras may have been sold with a stated TVL (TeleVision Lines). This is an older way of working out the resolution and are generally equivelant to a 1.3MP or lower camera.
If you are wanting to upgrade the cameras on an Analogue system it would be recommended to check the compatability of the DVR, as there will probably be a limit for some systems to what MP\resolution cameras are accepted by the recorder. This information should be available in the manual for your system or by searching for the make and model of your DVR.
Although there are differences between an IP and Analogue system interms of the way the camera connect to their recorders, supply power, communicate and resolution. The main operation of the recorders are the same. They will record and store the footage from the connected cameras and allow access to this footage via the recorder itself with an attached screen and mouse or with a Mobile app or computer software.
When using the system's accompanying mobile app or software this will require the recorder to be connected to your computer network and inturn probably the internet. This will not only allow you to access the system while connected directly to your network via an ether net cable or WiFi. It can also allow you to have access to the system while away from the property. This includes a Live view as well as recorded footage.
The main reason for the recorder (DVR and NVR) as the name suggest is to record the footage from the cameras. The footage is recorded to a HDD (Hard Disk Drive) installed in the system. The footage will be stored until the drive is full, where generally the oldest footage will start being over written to make way for the newer footage.
The HDD should be one designed specifically for operation in a CCTV system. These are currently available from 1 TB (TeraByte) all the way to 20 TB. The storage amount required is dependant on a few factors such as the number of cameras, the resolution of the cameras, type of recording and record schedule as well as how long you would like to keep footage for.
The amount of time that the system keeps the footage for can be up to yourself and what you are happy with. It is generally recommended to have at least 30 days worth of footage incase something is not noticed right after it has happened.
There are a couple of ways to stop recording un-needed footage instead of having the system recording 24/7. One would be to allow the system to record only when movement is detected in the field of view of the connected cameras. This will not only save alot of storage space, inturn allowing for a longer recorded time) it will also make finding any footage of something that may have occured easier without the need to watch hours of footage. As this will be marked on the timeline on the recorder or in the mobile app and software.
Another way is to use a schedule that will only have the system recording cameras between certain times. This can be for both motion activated, continuous recording or mixture of both. For example the system could be set to record continuosly during a businesses opening hours and then set to only record on motion while closed, when no one should be in the premises.