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

Trunks Definition Trunks are a large-bandwidth communication channels connecting switching centres, forming the core of the telephone network. A trunk comprises of a cluster of broadcast frequencies that are suitable for long haul communication of many voice and data signals simultaneously. Features The characteristic features of a trunk are − They carry digital information as opposed to analog signals carried by local loops. They are designed for both voice and data transmission. They can carry millions of calls simultaneously over long distances. They have very high bandwidth. They generally comprise of a cluster of fiber optic cables bundled together ... Read More

DefinitionPassive Optical Network (PON) is a FTTH (Fiber to the Home) technology deployed in both domestic and commercial consumers. It is called a passive network since it does not require a power equipment to amplify or process signals. A PON implements point – to – multipoint architecture, where a single optical line is divided into many optical splitters to serve multiple customers. It is used in the last mile of the network connection between an ISP and a user.ArchitectureThe passive optical network has three parts −Optical Line Terminator (OLT) − This is the end office of the service provider.Optical Distribution ... Read More

Definition Fiber to the home (FTTH) is a technology to deploy optical fibers in the local loop of the telephone networks to the users’ home for providing high-speed data connectivity. It replaces the existing copper wires as telephone lines to the customer premises by optical fibers that allow much greater bandwidth and less noisy connectivity. FTTH Council The FTTH Council is a non-profit organization to provide advanced FTTH solutions. Its members comprise of manufacturers, organizations and municipalities who build and install equipments for FTTH systems. The purpose of the Council is to share knowledge and build industry consensus on FTTH. ... Read More

DefinitionDigital Subscriber Line (DSL) is a communication technology that offers high – bandwidth digital communication over standard telephone lines formed of copper wires.FeaturesDSL is a family of technologies under the general name of xDSL, for various x, like ADSL, HDSL, and RADSL. Originally, it was a part of the Integrated Services Digital Network (ISDN) and was called IDSL.DSL technology is used in the local loop of the telephone network, i.e. the part of the telephone network that connects the customer premises with the end office of the telephone company.Some DSL services provide more than the standard bandwidth of the telephone lines. ... Read More

The shell is the command interpreter on the Linux systems. It the program that interacts with the users in the terminal emulation window. Shell commands are instructions that instruct the system to do some action.Some of the commonly used shell commands are −basenameThis command strips the directory and suffix from filenames. It prints the name of the file with all the leading directory components removed. It also removes a trailing suffix if it is specified.Example of basename is as follows −$ basename country/city.txtThis gets the name of the file i.e. city which is present in folder country.city.txtcatThis command concatenates and ... Read More

The interface between a process and an operating system is provided by system calls. In general, system calls are available as assembly language instructions. They are also included in the manuals used by the assembly level programmers.System calls are usually made when a process in user mode requires access to a resource. Then it requests the kernel to provide the resource via a system call.Types of System CallsThere are mainly five types of system calls. These are explained in detail as follows −Here are the types of system calls −Process ControlThese system calls deal with processes such as process creation, ... Read More

The loadable kernel modules in an operating system is an object file that contains code to extend the running kernel, which is also known as the base kernel. The loadable kernel modules are used to add support for file systems, hardware, system calls etc.An image that shows the loadable modules of the operating system is as follows −The different types of kernels in the operating system that may require loadable kernel modules are −MicrokernelA microkernel is the minimum software that is required to correctly implement an operating system. This includes memory, process scheduling mechanisms and basic inter-process communication.The microkernel contains ... Read More

Debugging is the process of finding the problems in a computer system and solving them. There are many different ways in which operating systems perform debugging. Some of these are −Log FilesThe log files record all the events that occur in an operating system. This is done by writing all the messages into a log file. There are different types of log files. Some of these are given as follows −Event LogsThese stores the records of all the events that occur in the execution of a system. This is done so that the activities of all the events can be ... Read More