Matrix Switches - Cisco 4116 - EtherFast Switch Design Manual

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RS-485 is a variation of the RS-422 standard and is based on a master-slave architecture, in which
the master initiates all transactions and the slave only transmits when instructed to do so by the
master. RS-485 allows up to 32 devices to communicate at distances up to 500 meters, but the
number of devices and distance can be extended using repeaters. A variety of connectors are
supported, including RJ11, RJ45, DB9 and DB25.
RS-485 offers a multi-drop capability, in which up to 32 cameras may be configured with unique IDs
to receive serial data. Figure 3 shows an example with four cameras that use the same RS-485 bus
to transmit PTZ data. A multi-drop configuration typically requires two terminations, one at each
end of the network.
Up-the-coax transmission, where electrical signals such as PTZ data communications are
transmitted over the same coaxial cable is not supported.
Figure 3. Multi-drop Bus Configuration

Matrix Switches

In a traditional video surveillance environment, a matrix switch is the core element of the solution. A
matrix switch acts as an array of video inputs and outputs, allowing users to control the display of
different cameras and to switch control of PTZ functions. Figure 4 shows a traditional CCTV system
with a matrix switch, where analog video streams are aggregated, controlled, and dispersed to
different monitor displays by using analog switching technology.
Figure 4. Traditional Matrix Switch
A typical matrix switch can be programmed to display a video stream from any camera on any
monitor either manually or by using automatic switching sequences. Some matrix switches include
salvo switching capabilities, which allow any number of monitors to be selected to switch as a
synchronized group. Also common is the ability to interface with external alarms or contact closures
and to display video that is triggered by designated events.
Design Guide
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