The critical section is a code segment where the shared variables can be accessed. An atomic action is required in a critical section i.e. only one process can execute in its critical section at a time. All the other processes have to wait to execute in their critical sections.A diagram that demonstrates the critical section is as follows −In the above diagram, the entry section handles the entry into the critical section. It acquires the resources needed for execution by the process. The exit section handles the exit from the critical section. It releases the resources and also informs 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 transferring of data from one process to another.A diagram that illustrates interprocess communication is as follows −The models of interprocess communication are as follows −Shared Memory ModelShared memory is the memory that can be simultaneously accessed by multiple processes. This is done so that the processes can communicate with each other. All POSIX systems, as well as Windows operating systems use shared memory.Advantage of Shared Memory ... 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 transferring of data from one process to another.One of the ways to manage interprocess communication is by using sockets. They provide point-to-point, two-way communication between two processes. Sockets are an endpoint of communication and a name can be bound to them. A socket can be associated with one or more processes.Types of SocketsThe different types of sockets are given as follows −Sequential Packet Socket: This type ... Read More

There are many operations that can be performed on processes. Some of these are process creation, process preemption, process blocking, and process termination. These are given in detail as follows −Process CreationProcesses need to be created in the system for different operations. This can be done by the following events −User request for process creationSystem initializationExecution of a process creation system call by a running processBatch job initializationA process may be created by another process using fork(). The creating process is called the parent process and the created process is the child process. A child process can have only one ... Read More

Context Switching involves storing the context or state of a process so that it can be reloaded when required and execution can be resumed from the same point as earlier. This is a feature of a multitasking operating system and allows a single CPU to be shared by multiple processes.A diagram that demonstrates context switching is as follows −In the above diagram, initially Process 1 is running. Process 1 is switched out and Process 2 is switched in because of an interrupt or a system call. Context switching involves saving the state of Process 1 into PCB1 and loading the ... Read More

Global System for Mobile communication (GSM) architecture comprises of the following components −Mobile Station : The mobile station is the mobile phone, which comprises of the mobile handset and SIM card. The mobile handset comprises of the transceiver, the display and its processor. SIM stands for SubscriberIdentity Module. It is a removable chip that contains account information of the subscriber and connects the handset to the mobile network system.Air Interface : The air interface is the interface between the mobile station and the Base Transceiver Station. It is also called the UM interface as it is analogous to U interface ... Read More

Global System for Mobile communication (GSM) is the most widely used digital mobile telephony system. GSM technology was first launched in Finland in 1991. It was developed by European Telecommunications Standards Institute (ETSI) to describe the protocols for 2G mobile communications.Presently, GSM comprises of approximately 90% of mobile connections worldwide. Features Original 2G standard was a digital, circuit-switched, full duplex network. GSM is part of the evolution of wireless mobile telecommunications including High-Speed Circuit-Switched Data (HSCSD), General Packet Radio Services (GPRS), Enhanced Data GSM Environment (EDGE), and Universal Mobile Telecommunications Service (UMTS). GSM operates at either 900 MHz ... Read More

Digital Advanced Mobile Phone System (D-AMPS)is a digital version of Advanced Mobile Phone Systems (AMPS), the original analog standard for cellular phones. D-AMPS uses a combination of time division multiple access (TDMA) and frequency division multiple access (FDMA). It adds TDMA to get three channels per AMPS channel, thus tripling the number of calls on a channel. Features They are standardised by IS-54 and IS-136. As in AMPS, D-AMPS also uses frequencies from 800 to 900MHz for transmission. Half of the spectrum is used for sending signals and the other half is used for receiving signals. The frequency ... Read More

Second generation (2G) mobile phones switched from analog system of 1G to digital system. It was commercially launched in 1991 as GSM standard in Finland. As with 1G phones, 2G phones didn’t have any worldwide standardizations. 2G systems were also known as personal communications services (PCM). Advantages of 2G over 1G It allows voice signals to be digitized and compressed. So, they are more efficient on frequency spectrum than 1G. They introduced data services for mobile in form of SMS text messaging. Data and voice signals are digitally encrypted. So, security against eavesdropping and fraud increased manifold. Digital signals ... Read More

Frequency division duplex (FDD) is a communication technique where the connected parties can communicate with each other in both directions through use of separate frequency bands for transmitting and receiving. Since FDD uses different frequency bands for upstream data and downstream data, the sending and the receiving signals do not interfere with each other. FDD in Cellular Networks Cellular networks use FDD to separate the channels. One block of the electromagnetic spectrum is allocated for uplink, which carries data from mobile phones to a base station. A different block of the spectrum is allocated to downlink, carrying data ... Read More