Saturday, March 21, 2009

77. IP controllers.

Controllers are connected to a host PC via Ethernet LAN or WAN. Advantages:An existing network infrastructure is fully utilized, there is no need to install newcommunication lines. There are no limitations regarding the number of controllers (32 per line in case of RS-485). Special RS-485 installation, termination, grounding and troubleshooting knowledge is not required.

Communication with controllers may be done at the full network speed, which is important if transferring a lot of data (databases with thousands of users, possibly including biometric records). In case of an alarm controllers may initiate connection to the host PC. This ability is important in large systems because it allows to reduce network traffic caused by unnecessary polling. Simplifies installation of systems consisting of multiple sites separated by large distances. Basic Internet link is sufficient to establish connections to remote locations.

Wide selection of standard network equipment is available to provide connectivity indifferent situations (fiber, wireless, VPN, dual path, PoE) disadvantages:The system becomes susceptible to network related problems, such as delays in case of heavy traffic and network equipment failures. Access controllers and workstations become may become accessible to hackers if the network of the organization is not well protected. This threat may be eliminated by physically separating the access control network from the network of the organization.

Also it should be noted that most IP controllers utilize either Linux platform or proprietary operating systems, which makes them more difficult to hack. Industry standard data encryption is also used. Maximum distance from a hub or a switch to the controller is 100 meters (330 ft). Operation of the system is dependent on the host PC. In case the host PC fails, events from controllers are not retrieved and functions that required interaction between controllers (i.e. anti-passback) stop working. Some controllers, however, have peer-to-peer communication option in order to reduce dependency on the host PC.

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