A VMS is employed to provide recording, streaming, switching and multiplexing functionality. It can normalize streaming video from multiple sources into a common format as well as provide recording and playback services. It also functions as a video server by relaying video to multiple endpoints, each with different resolution and bit rate requirements.

VMS functionality increasingly runs as software on enterprise servers instead of on custom embedded hardware. A single server can handle the recording and streaming tasks for 64 or more cameras, with video stored on internal drives or on a storage-area network. Management software typically combines a database server and a Web server, which enables configuration and monitoring over the network and notification to mobile endpoints.Infrastucture planning

A medium to large deployment can involve hundreds if not thousands of cameras distributed over tens or hundreds of locations. Most security policies require video to be stored for a week to a month, and some require it to be archived for a year or longer. The operational and maintenance costs over the lifetime of such a system can easily exceed the upfront capital expenditure.

For illustrative purposes, let's examine a 1,000-camera system spread over 10 sites streaming at 4Mbps per camera. If recording is done locally at each facility, it consumes 400Mbps on the LAN and 4.3TB of storage per day per site. With a one-month retention policy, over a petabyte of storage is needed for all sites. It is also likely that monitoring operations are centralized in a security/network operations center, which requires video to be streamed to a remote site with dedicated WAN links at hundreds of megabits.

Given these challenges, enterprises are forced to compromise a great deal. One option is to limit video surveillance to forensic evidence — i.e., no active streaming or monitoring, with recorded video reviewed only after an incident occurs. Other options include dropping the resolution and frame rate for video streamed over a WAN, which makes it difficult to detect security violations.