Get on the Bus
Q: What is the bus or backbone topology?
A: A linear bus topology is a system where all devices connect to a single main cable or backbone. A terminator is required at cable end to absorb the signal and prevent it from reflecting back across the bus. Signals are broadcast to all stations. Each device checks the address on the signal as it passes along the bus. If the signal's address matches that of the device, the device processes the signal. If the address doesn't match, the device just passes the signal down the bus. Only one device can talk' on a network at a time. Procedures are put in place to handle the collisions that occur from multiple signals. Devices in the bus topology are passive and simply listen' for a signal; they do not boost or amplify the signal.
Bus topologies can use twisted pair, coaxial or fiber optic cable and are easy to connect and require less cable length than a star topology. The entire network shuts down if there is a break in the main cable and the break can be difficult to identify. Required terminators can add labor and cost.
Achieve Precise Door Status
Dortronics Systems, Inc. offers an enhanced version of its versatile 7600 Annunciator Monitoring and Control Series. The modular system, expandable in four zone increments, can be configured to provide precise monitoring and control of over 100 doors/zones. The 7600 Annunciators provide greater capacity for large scale and complex access control applications.
The 7600 Annunciator Series panels are available for console or rack mounted use and can be hardwired or multiplexed. The units feature tri-state LEDs for each zone to visually indicate when a door is: closed and locked; closed and unlocked; opened with authorization; forced or held open; unsecured; and when an alarm has been sounded.
Doors can be remotely unlocked to allow momentary access or extended free access using the 7600 Annunciator Series panels. The panels are compatible with most NFPA compliant delayed egress systems. When used with Dortronics 101 Delayed Egress System, the status of each door is displayed on the unit and unauthorized exit attempts are reported as alarms. This device can also be used with the 7200-PT series Door Prop Alarms to provide feedback to security personnel when a door has been left unsecured. The 7600 Annunciator Series panels also monitor authorized ingress and egress by way of independent access control system or by manual station control hardware such as a key or keypad. For more information, visit www.dortronics.com
Q: How does a star topology compare?
A: All of the devices in a star topology are directly connected with twisted pair, coaxial or fiber optic cable to a central unit called a hub, concentrator or router. Data passes through the central unit that manages and controls all functions of the network and acts as a repeater for the data flow.
Star Topology systems are easy to install and wire. The network is not disrupted when individual faults occur or devices are connected or removed. The system requires more cable length than a linear topology and attached device are impacted if a related hub, router or concentrator fails. Cost of concentrators adds to system cost. The star topology is probably the most common form of network topology currently in use.