communicates with the control panels which collect data on events and alarms
from peripheral devices.
The connection and communications between the control panels and the
host computer generally occur using one of two methods. One is through an
RS-232 or RS-485 communication from the host computer to the control
panels. Typically this is accomplished by looping or “daisy chaining” a con-
nection from control panel to control panel with all control panels accessing
the host computer through the first control panel on the loop. The second
and emerging technique is to have the host computer and the control panels
on a network using IP protocols and standard structured cabling.
The user database for the access control system has profiles or credentials for
every authorized user relating to levels and parameters. This database can be
centralized in the host computer or distributed among the control panels with
the host computer still having the complete database. This distributed network
architecture is used to “push” the system decision making out to the local control
panel, thus reducing communications traffic to the host computer.
For instance, when a person arrives at a door and presents an access card
with encoded credential information to a card reader that information is then
passed to the local control panel. In a centralized database system, the control
panel passes the information on to the host computer with additional informa-
tion regarding the location of the door and the time the card was presented.
The host computer then verifies the information and compares the access level
to the door location and the time of day. Upon verification, the host computer
sends a command to open the door to the control panel and the person is
allowed access to the building (Fig. 6.2).
In distributed database architecture a control panel with onboard memory
contains the database for the doors and locations that it monitors. The control
panel verifies the credential information without communicating to the host
computer. The control panel later sends all transaction data to the host com-
puter for system archiving. This distributed method can operate even if
communication with the host is lost, including storing and buffering transac-
tion data for sending to the host computer when communication is restored.
In addition to the database controlling cards and access levels the host com-
puter is capable of producing administrative reports and creating users’ badges.
The badging system at the host computer typically includes a camera, backdrop
and badging printer. Badging stations may be established in an organization’s
human resources or security department; anywhere employees, visitors, students,
and others are entering or exiting the organization.
The software on the host system has features to facilitate the security opera-
tions. It may have the ability to supply an automatic notification, allowing
security personnel to be notified via a PDA or email when a particular person
Access Control Systems 71