Access Control System Overview

Security Access Control System
 Basic Elements and Architecture

Physical Security and Access Control Systems have become necessary for most companies. Large or small, companies need to protect their facilities, data, and personnel. The following provides a cursory look at what is involved in a Physical Security and Access Control System, elements and architecture, with a description of its components.

Fig. 1: General Access Control System Architecture

Why implement an Access Control System?

-Provide “Controlled Access” to the facility
-Allow access only to authorized personnel for each area
-Implement a ‘Security Protocol & Policy’ to make employees, visitors, and the facility safe
-Implement a security and access level hierarchy based on personnel function
-Automate and enhance the identification process
-Automate personnel tracking
-Minimize human error
-Track outside contractors and vendors
-Record and generate reports of access for each area

-Eliminate the need to man all access points
-Take full, and orderly control of your site
-Improve security measures and provide convenient access for authorized personnel
-Improve response to emergencies
-Ability to lock down entire areas quickly at high threat levels
-Track personnel movement and access
-Establish and enforce one set of access rules
-Eliminate the “buddy” system
-Provide safety for visitors and employees
-Archive records for potential future use

The following is a brief description of components comprising an access control system. Referring to the diagram above, each element is numbered and briefly described. All these parts are required, in one form or another, to secure your facility. You may not think about the process, but when you present your card to a reader, or a biometric device, a lot of things happen before the door opens to allow entry.

The Access Control System (ACS) Server (1) runs the software. It may contain many servers in one machine, or distributed amongst many machines. This server is responsible for assigning access to, and tracking traffic in secure areas. It maintains a database of credential holders, and their access level. It also communicates with ACS panels to download specific data to each panel for local storage. There are various methods this server could communicate with the ACS panels. If the panels are equipped with Network cards, the communication could be TCP/IP based. If the panels are equipped with RS-485 multi-drop interface, then the server, (via an RS-232 to RS-485 converter (4)), will communicate with each panel on the serial bus, polling each panel, and processing the panel data. The ACS Server can also provide a “host grant” upon request from panels that do not have the most up-to-date information. The ACS server refreshes the panels on a scheduled basis, however, in the meantime the personnel will be provided with host grant until such time.

The Badging Server (2) is where authorized personnel’s data is kept. The server will process the data and issue (print) credentials (badges). Normally, the employee, or contractor receives a badge with numerous information encoded, including a photo, name, address, organization, date of issue, access areas, expiration date, restrictions, and other necessary information. If biometric readers are employed at the site, a sample of finger print, or iris scan may be encoded as well. The Badging Server is networked with the ACS server so badges can be updated in the ACS Server database, and downloaded to the access panels where the credential holders are allowed access. This download takes place when changes are made to the access areas, personnel, access levels, etc.

Ethernet Router or Switch (3) {self explanatory}

RS-232 to RS-485 Converter (4): RS-232 is a serial interface with parallel control lines to control the flow of data. Not all signals are necessary in all cases. The serial port of a computer uses pins 2, 3, and 5. RTS line is usually looped to CTS for non-flow control applications, and since there is no phone modem, RI and CD are not used. RS-232 uses “single-ended” drivers, and receivers. The table below describes the signal names and the associated pins.

Pin Description	Symbol	Pin Number
Carrier Detect	CD	1
Receive Data	RD	2
Transmit Data	TD	3
Data Terminal Rdy	DTR	4
Signal Ground	SG	5
Data Set Ready	DSR	6
Request to Send	RTS	7
Clear to Send	CTS	8
Ring Indicator	RI	9

Table 1: 9-pin RS-232 (computer com-port) signal description

RS-485 is a differential multi-drop bus. Only data and ground lines connect to all devices.
 

Fig. 2: RS-485 Multi-drop interface with differential drivers and receivers. Click on the link for a short overview of Serial Multidrop Bus Protocol.

The video router/switch (5) provides the capability of observing any camera, or a multiplexed view in the system client workstation.

The digital video recorder (6) is usually on, recording the events on a loop basis. The duration of the loop is based on the customer requirements. There are many cameras in a large enterprise system, and there maybe many recorders as well. Recorders are usually assigned to a limited number of cameras based on their storage capacity, but none-the-less, are necessary to exist on the same IP network so events can be recalled, and replayed on-demand, per area.

The control Panels (7) provide the gateway between the control points (door, checkpoint) and the ACS server. On the door side, they process the reader data, report the door position (open, closed), accept a request to exit from the secure side, and order the electric door strike to open, or remain closed. On the server side, they respond to polls, report intrusion, alarms, credential problems, tamper alarms, and a number of other information as required to make the area safe. Panels hold user credential data on local memory in case the communication between the panel and the server is unavailable. Panels will operate on stand-alone until the communication is restored. There are many flavors of panels, and interfaces connecting the panel to the server. Some panels communicate with the server on Ethernet protocol, some on RS-485 multi-drop bus. On the check-point side, however, the signals are fairly standard. The garden variety panels normally control 2 check-points (doors), but there are panels with expansion slots that can extend to several doors. A typical panel-door connection is shown below (Honeywell® NS2+):

Fig 3: Typical wiring from the Control Panel to the door hardware  

Door Hardware (8) is composed of a reader, door position switch, request to exit button, and an electric door strike. There are many varieties of readers, with different technologies. Wiegand format data (data0, data1), Magnetic stripe format (data, clock), and biometric decoders (finger print readers, Iris scanners). The readers employ a wire winding to produce a magnetic field. When a card is presented to the reader, the magnetic field produces an electric field in the card winding, supplies power to the processor in the card, and the data packet containing the user information is transferred from the card to the reader. The reader transmits the data to the control panel, which actuates a relay to apply power to the door strike to open (if the user has access), or report an invalid card (if the user does not have access to the area). There are many card formats used in the industry ranging from 26-bit to FIPS-201 compliant formats with FASC-N length of 200 bits. Many organizations exceed the 200-bit card format, extending to 512, or 1024 bits.

Reader examples:

Door position switch is usually a magnetic switch. While both parts of the switch are in proximity of each other, the switch is closed, otherwise open.

Electric strike is a solenoid actuated device that releases the lock so the door can be pushed without turning the door knob or handle. The input power is 12, or 24 Vdc. In some cases, magnetic locks are employed so when energized, the door is magnetically held by the door frame part of the lock.

Request to exit / Egress is a momentary closure switch that is normally de-bounced. When pressed, the circuit closes and signals the panel to release the door lock, allowing graceful exit from a secure area.

Wireless Access Control System eliminates wiring, trenching, conduit installation, core drilling, asbestos abatement, and variety of problems associated with installation. The connection between the ACS server and panels can be done wirelessly using WILDR-MIU. Also, the connection between any panel and a checkpoint or a door can be implemented by WILDR-MIU1. All panel to door connections are handled by WILDR-MIU1. WILDR-MIU1 also supplies power to the door strike and the reader eliminating the requirement for an extra battery. Please visit the services tab, wireless, for detail information.
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