09-05-2014, 03:07 PM
Communication Networks
Communication Networks.ppt (Size: 502 KB / Downloads: 10)
Bus Network
In bus network, all stations are attached to a single cable.
When a station sends a message, it is broadcast down on the cable in both directions. Terminators at the end of the cable prevent the signal from reflecting back to the sender.
All stations on the cable constantly monitor for messages meant to them. When a station detects a message meant for it, it reads the message from the cable and the other stations will ignore it.
Since all stations are sharing the same cable, some form of control is needed to make sure which station will transmit when, otherwise there will be a collision.
Advantages: Easy to wire, quick response, less expensive, and if one station dies, it has no effect on the total network.
Disadvantage: However bad connection to the cable can short it and bring down the entire network
Star Network
In star network, each station is connected via a point-to-point link to a central point.
This central point is called hub, multi port repeater, or concentrator.
The central point may be “passive”, “active”, or “intelligent”.
A passive hub simply connects the arms of a star, no signal regeneration is performed.
An active hub is like a passive hub, except that it regenerates signals.
Intelligent hubs not only regenerate signals but also perform activities such as intelligent path selection and network management.
Advantage:
The main advantage of the star architecture over the bus is its small excess loss, since in case of n-user star the excess loss increases logarithmically with n, while in case of n-user bus it increases linearly with n.
Disadvantage:
Since all information in a star network goes through a central point, stars are easy to troubleshoot.