Access Control 13
Access Control 13 : Physical security: (6) Access control system topologies: Access control System Using Serial Controllers: (1) Serial Controllers: Disadvantages: (a) RS-485 does not allow Star-type wiring unless splitters are used; (b) RS-485 is not well suited for transferring large amounts of data (i. e. configuration and users). The highest possible throughput is 115. 2 kbit/s, but in most system it is downgraded to 56. 2 kbit/s or less to increase reliability. (c) RS-485 does not allow the host PC to communicate with several controllers connected to the same port simultaneously. Therefore in large systems transfers of configuration and users to controllers may take a very long time and interfere with normal operations. (d) Controllers cannot initiate communication in case of an alarm. The host PC acts as a master on the RS-485 communication line and controllers have to wait until they are polled. (e) Special serial switches are required in order to build a redundant host PC setup. (f) Separate RS-485 lines have to be installed instead of using an already existing network infrastructure. (g) Cable that meets RS-485 standards is significantly more expensive than regular Category 5 UTP network cable. (h) Operation of the system is highly dependent on the host PC. In case the host PC fails, events from controllers are not retrieved and functions that require interaction between controllers (i. e. anti-passback) stop working. Access control system using serial main and sub-controllers
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