STAR’ TOPOLOGY VS. ‘BUS’ TOPOLOGY
This is a general comparison between Videodidact as a representative of a star system and systems that use the BUS topology technique.
General
In a system that uses a STAR topology, each computer is connected to a central unit using a separate, independent cable run to each workstation.
In a BUS topology, a single cable is used to connect all computers in a loop, one computer to the next, and so on.
Installation of a BUS style system is relatively easy and the cost is slightly lower. However, that’s where the benefits end. Due to the use of a single transmission cable the following problems are very common:
* Less reliability, * Poorer Video Quality, * Tough troubleshooting, * Difficult user interface.
Reliability
If any computer in a BUS system malfunctions the entire computer classroom may become unstable. For example, if the interface of station #5 stops functioning correctly, the reaction of station #6 and all following stations is uncertain. If the main unit fails, all computers in the whole classroom may not work correctly anymore. This can be tested by unplugging the main unit of a bus system during operation. Additionally, all computer interfaces (boosters) connected in a BUS topology normally need separate electrical power. Powered devices have a greater chance to damage internal electronic components of hardware equipment.
In a STAR system, if any one computer malfunctions all the other systems will function normally…uninterrupted. If the central unit was ever to fail, all the computers will operate automatically in a “stand-alone” environment. No interruption of training will appear. Moreover, a STAR system does not need any electrical power within the entire cabling.
Quality
The most sensitive signal in a computer is the video signal. The quality of this signal deteriorates with every connection between the source (computer) and the monitor. This is a physical rule and can not be absorbed by any manufacturer.
In a system, following the STAR Topology, every Student, as well as the Instructor is directly connected to the central unit. As a result, whenever the Instructor sends an image to the Student(s), the central unit sends this image to each student directly at the same time. This ensures quality and real time delivery across the board, thereby avoiding any degradation or delay.
In a system following the BUS topology the image of the instructor is going to the first Student then to the second Student, then to the third Student, and so on, respectively.
Unfortunately as the signal travels along in the BUS line from Student to Student, the signal deteriorates more and more. This is the reason why a BUS system should really not support more than 10 to 15 students without amplifying the video signal with line booster, expanders or extenders.
As previously mentioned, one problem with using these devices is that they require electrical power to work. This power source can create interference on the video signal. Secondly, the use of signal boosters do not make the video signal better, just stronger. For example, if the picture quality has already been deteriorated slightly, than a booster can only make this already deteriorated picture stronger, not better. In addition, these boosters not only amplify the already weak video signals but also amplify any interference or noise that is present on the cable.
No boosters, expanders, or extenders are needed in a STAR system. The picture quality in a STAR system will be excellent to all stations even if there are more than 40 workstations in the classroom.
Troubleshooting
Isolating a problem in a STAR configuration is very simple. For example, if there is a problem with Station #5, we know to check the hardware and the cable associated with station #5 only.
In a BUS system, due to the many computers that are connected onto the same cable, it is much more difficult to isolate a problem.
Operation
The user interface on a STAR configuration is generally straightforward due to the independent cable runs used to connect each student directly to the central unit. Most commands can be executed with a single keystroke.
A BUS system, conversely, relies on a single cable to send all commands and the video signals over. Therefore a number of function sequences must be entered to direct the signals. Comparatively, count how many keystrokes are required to send a signal from station #12 to station #16. Using STAR topology, the instructor would press only two keys; first a key labeled 12 followed by key labeled 16. Simple!
Also other features such as Interactive Remote Control are normally not available by systems using the BUS topology.
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