We all know that the benefits of IP-based networked CCTV are significant compared to traditional analog systems. But the real benefit of IP video can only be realized if the solution is based on a truly distributed architecture.
Serious scalability problems arise when an IP-CCTV system is based on a Centralized Architecture. Instead, a Distributed Architecture delivers a flexible and scalable solution than can lead to systems being deployed across sites, cities and countries.
Storing IP video data
There are typically two different approaches to storing data in an IP video system. A centralized architecture uses a master database usually located in the central control room or head office. A distributed architecture spreads the data around the security management system, generally keeping it close to where it is produced or needed.
The stored data can be categorized into two types: configuration and live.
Configuration data is site information specifying the design and make-up of the security management system. Examples of configuration data include lists of cameras, lists of users, user permissions, site structure, maps representing the layout of the system and licensing information. After the initial installation and commissioning stages of a security management system, configuration data is not routinely changed. It is however routinely accessed by operators when logging into the system.
Live data is typically CCTV video recordings and alarm information. Live data is accessed continuously during normal security management operations, either by devices recording the data or operators reviewing the data.
Configuration data is usually held in a database called the Site Database. This makes it easy for administrators to make and manage changes; however it also creates a problem. When an administrator makes a change to the site database how do the users, distributed throughout the security management system, get the change?
The obvious and easy solution is to have the site database held centrally on a master database server and have all users access the master server over the network. This is called a centralized architecture.
Many systems use a centralized architecture for storing more than just configuration data. They may also use it for storing live data such as video recordings or alarm data.
Figure 1 shows a security management system consisting of one or more sites each with its own local area network (LAN) connected to a central office. The central office is also where the central file server is located, hosting the site database. Also in the central office are network video recorders (NVRs) for recording video and alarm data.
Every camera and workstation in each remote office must regularly, and in some cases continuously, communicate with the central office in order to check for changes and updates in the site database. This includes checking for valid licenses or storing recording and alarm data.
A centralized architecture causes four major problems:
- Cost: All users continuously communicate with the central office. On a local area network (LAN) that means buying expensive high-end switches and on a wide area network (WAN) it means using up precious bandwidth.
- Reliability and resilience: What happens when the WAN or core LAN switch breaks? Remote users can be left stranded with no access to the live and recorded video from cameras which are actually located locally to them on a working LAN.
- Single point of failure: What happens if the server hosting the site database fails? All users of the system rely on access to the site database, for example, to get log-in credentials verified or license permissions checked. If the site database server fails, the whole security management system goes down.
- Scalability: As more cameras and users get added to each remote office and as more remote offices get added to the network, everything gets congested. The local LANs, WAN links and central server all get congested coping with increasing levels of traffic checking for site database changes, valid licensing and storing recordings and alarms.