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Hub, repeater, switch, router, gateway, bridge

HUB Hub is a controller that controls the traffic on the network.  The following important properties of hub are:  1) It amplify signals. 2) It propagates signals through the network. 3) It does not require filtering. 4) It does not require path determination for switching. 5) It is used as network concentration points. Hubs are basically two types: 1) Active hub 2) Passive hub Active hub: A ctive hub works as repeater which is a hardware device that regenerates the received bit pattern before sending them out . Passive hub : A passive hub is a simple hardware device which provide a simple physical connection between the attached devices. Advantages of hub: It cannot filter the traffic full stop feeling generally refers to a process or device that screens network traffic for certain characteristics such as source address and destination address and protocol. Disadvantages of hub: On a hub, more than one user may try to send data on the netwo...
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Generalization and Specialization

Generalisation is an abstraction for sharing similarities among classes while preserving their differences. For example, each piece of equipment has a manufacturer weight and cost . Pumps also have suction pressure and flow rate. Tank also have volume and pressure we would like to define equipment features just once and then add details for pump, tank and other equipment types. Generalisation is a relationship between a class and one or more refined versions of it. The class being refined is called superclass and each refined version is called a subclass. For example equipment is the superclass of pump and tank. Attributes and operations common to a group of subclasses are attached to the superclass and shared by each subclass. Each subclass is set to inherit the feature of its superclass, for example, pump inherites attributes manufacturer, weight and cost from equipment. Generalisation is sometimes called the "is-a" relationship because each instance of a subclass is ...
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Scheduling: preemptive scheduling

Preemptive Scheduling : In contrast to non preemptive scheduling, a scheduling decision can be made even while the job is executing whereas in non preemptive scheduling, a scheduling decision is made only after job completes its execution. Therefor preemptive scheduling may force a job in execution to release the processor, so that the execution of some other job can be undertaken, in order to improve throughput considerably. Types of preemptive scheduling: 1) Round Robin scheduling algorithm : the round Robin scheduling is designed for time sharing systems. The primary objective of round Robin scheduling are interactive use, good response time and sharing the resources equitable among processes. It is similar to FCFS, but preemption is added to switch between processes. The processes are alocated a small unit of time. Known as time Quantum or time slice is in rotation until the completion of processes. To implement round Robin scheduling, a FIFO(first in first out) queue...
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