Packet switching is a connectionless network switching technique. Here, the message is divided and grouped into a number of units called packets that are individually routed from the source to the destination. There is no need to establish a dedicated circuit for communication. Process Each packet in a packet switching technique has two parts: a header and a payload. The header contains the addressing information of the packet and is used by the intermediate routers to direct it towards its destination. The payload carries the actual data. A packet is transmitted as soon as it is available in a node, ... Read More

Circuit switching is a connection-oriented network switching technique. Here, a dedicated route is established between the source and the destination and the entire message is transferred through it.Phases of Circuit Switch ConnectionCircuit Establishment : In this phase, a dedicated circuit is established from the source to the destination through a number of intermediate switching centres. The sender and receiver transmits communication signals to request and acknowledge establishment of circuits.Data Transfer : Once the circuit has been established, data and voice are transferred from the source to the destination. The dedicated connection remains as long as the end parties communicate.Circuit Disconnection ... Read More

Definition Network switching is the process of transmitting data packets from the source to the destination through a number of intermediate network nodes. Here, each node controls or switches data packets to the next node towards the destination. When data comes on a node it is called ingress, and when data goes out of a node it is called egress. Switching Methods The two broad level switching methods are connection oriented switching and connectionless switching. Connection – oriented Switching : In connection – oriented switching, a dedicated path is established between the source and the destination before data switching. ... Read More

Wavelength division multiplexing (WDM) is a technique of multiplexing multiple optical carrier signals through a single optical fiber channel by varying the wavelengths of laser lights. WDM allows communication in both the directions in the fiber cable. Concept and Process In WDM, the optical signals from different sources or (transponders) are combined by a multiplexer, which is essentially an optical combiner. They are combined so that their wavelengths are different. The combined signal is transmitted via a single optical fiber strand. At the receiving end, a demultiplexer splits the incoming beam into its components and each of the ... Read More

Interprocess communication is the mechanism provided by the operating system that allows processes to communicate with each other. This communication could involve a process letting another process know that some event has occurred or the transferring of data from one process to another.A diagram that illustrates interprocess communication is as follows −Synchronization in Interprocess CommunicationSynchronization is a necessary part of interprocess communication. It is either provided by the interprocess control mechanism or handled by the communicating processes. Some of the methods to provide synchronization are as follows −SemaphoreA semaphore is a variable that controls the access to a common resource ... Read More

A zombie process is a process whose execution is completed but it still has an entry in the process table. Zombie processes usually occur for child processes, as the parent process still needs to read its child’s exit status. Once this is done using the wait system call, the zombie process is eliminated from the process table. This is known as reaping the zombie process.A diagram that demonstrates the creation and termination of a zombie process is given as follows −Salient points of Zombie ProcessesSome of the salient points related to zombie processes are as follows −All the memory and ... Read More

Process Control Block is a data structure that contains information of the process related to it. The process control block is also known as a task control block, entry of the process table, etc.It is very important for process management as the data structuring for processes is done in terms of the PCB. It also defines the current state of the operating system.Structure of the Process Control BlockThe process control stores many data items that are needed for efficient process management. Some of these data items are explained with the help of the given diagram −The following are the data ... Read More

A process is an active program i.e a program that is under execution. It is more than the program code as it includes the program counter, process stack, registers, program code etc. Compared to this, the program code is only the text section.A program is not a process by itself as the program is a passive entity, such as file contents, while the process is an active entity containing program counter, resources etc.Process StatesA process changes its state as it executes. This state partially depends on the current activity of a process. The different states that a process is in ... Read More

Pulse code modulation (PCM) is a technique of digitally representing analog signals. It takes samples of the amplitude of the analog signal and changes it to binary data. PCM technique is used by codecs in telephone networks to convert analog signals in local loops to digital signals in the trunks, and reverse conversion at the receivers’ end. Operations in Pulse Code Modulation The operations in PCM technique involves operations at the transmitting end and the operations at the receiving end. Transmitting End − In the transmitting end, the analog signals are sampled, quantized and encoded. The codec samples the analog ... Read More

Analog Telephone Cores The early telephone networks had analog cores. Frequency division multiplexing (FDM) was used to transmit a number of voice signals over the single line. Twelve calls were multiplexed into a group. Five groups were multiplexed into a supergroup. Digital Telephone Cores The present telephone networks have digital cores. This requires that the analog signals in the local loops are converted to digital signals that are transmitted via the trunks. This is done by codec (coder decoder). Time division multiplexing (TDM) is used to multiplex digital signals in the trunks, since it can be entirely handled by digital ... Read More