The network allocation vector (NAV) is a virtual carrier sensing mechanism that forms an important part of the carrier sense multiple access with collision avoidance (CSMA/CA). It is implemented in wireless network protocols, IEEE 802.11 and IEEE 802.16, which operates in the medium access control (MAC) layer.TechniqueThe network allocation vector can be considered as a counter that counts down to zero. The maximum NAV duration is the transmission time required by frame, which is the the time for which the channel will be busy. At the start of transmission of a frame, the NAV value is set to its maximum. ... Read More

Point coordination function (PCF) is an optional technique used to prevent collisions in IEEE 802.11-based WLAN standard including Wi-Fi. It is a medium access control (MAC) sublayer technique used in areas where carrier-sense multiple access with collision avoidance (CSMA/CA) is used.PCF is used additionally along with the mandatory distributed coordination function (DCF). It is used in centralised control system, and is present in the access point (AP) of the wireless network. An AP is generally a wireless router that coordinates network communication.Features of PCFIt is an optional function that resides on the top of the mandatory DCF. Both PCF and ... Read More

Distributed coordination function (DCF) is a mandatory technique used to prevent collisions in IEEE 802.11-based WLAN standard (Wi-Fi). It is a medium access control (MAC) sublayer technique used in areas where carrier-sense multiple access with collision avoidance (CSMA/CA) is used.TechniqueThe basic technique of DCF is as follows −When a station has a frame to transmit, it waits for a random backoff time. The random backoff time is defined by a contention window having a random number of time slots. The backoff time is given by the following equation −Timebackoff = random()×TimeslotsHere, the function generates a random number and is the ... Read More

IEEE 802.11 standard, popularly known as WiFi, lays down the architecture and specifications of wireless LANs (WLANs). WiFi or WLAN uses high frequency radio waves instead of cables for connecting the devices in LAN. Users connected by WLANs can move around within the area of network coverage.The 802.11 MAC sublayer provides an abstraction of the physical layer to the logical link control sublayer and upper layers of the OSI network. It is responsible for encapsulating frames and describing frame formats.MAC Sublayer frame of IEEE 802.11The main fields of a frame of wireless LANs as laid down by IEEE 802.11 are ... Read More

In wireless communications, when multiple antennas are used both at the transmitting end as well as the receiving end, the configuration is said to be multiple input, multiple output or MIMO. MIMO helps in sending and receiving multiple data signals simultaneously over the same radio channel. MIMO is a smart antenna technology, the other popular technology being multiple input, single output (MISO) and single input, multiple output (SIMO).The following diagram shows MIMO configuration −Advantage of MIMO over Traditional Wireless SystemsIn traditional wireless communication systems, a single antenna is used at the transmitter site, and another single antenna is used at ... Read More

Here we will see the md5sum command in Linux system. The MD5 is one of the Message Digest algorithm, that generates hash values to create checksum for the messages. It helps to identify if the integrity is maintained or not. Here we will see some example of md5sum command in Linux system.If we use this command on a string, it will generate a hash value, if we create some minor change in the text, it will generate massive change in the checksum.Examplesh-4.4$ echo 'Hello World' Hello World sh-4.4$ echo 'Hello World' | md5sum e59ff97941044f85df5297e1c302d260 - sh-4.4$If we change the content ... Read More

An operating system (OS) is basically a collection of software that manages computer hardware resources and provides common services for computer programs. The operating system is a crucial component of the system software in a computer system.These are some few common services provided by an operating system −Program executionI/O operationsFile System manipulationCommunicationError DetectionResource AllocationProtectionIn the matter of multi-user or multi-tasking environments, resources such as main memory, CPU cycles and files storage are to be allocated to each user or job. Some major activities of an OS with respect to resource management are −The Operating System manages all kinds of resources ... Read More

An operating system (OS) is basically a collection of software that manages computer hardware resources and provides common services for computer programs. Operating system is a crucial component of the system software in a computer system.These are some few common services provided by an operating system −Program executionI/O operationsFile System manipulationCommunicationError DetectionResource AllocationProtectionErrors can occur anytime and anywhere in operating system. An error can occur in CPU, in I/O devices or in the memory hardware. Some major activities of an operating system with respect to error handling are−The Operating System constantly checks for possible errors.The Operating System takes an appropriate ... Read More

Processes that executing concurrently in the operating system may be either independent processes or cooperating processes. if a process cannot affect or be affected by the other processes executing in the system then the process is said to be independent. So any process that does not share any data with any other process is independent. A process is said to be cooperating if it can affect or be affected by the other processes executing in the system. So it is clear that, any process which shares its data with other processes is a cooperating process.There are many reasons for providing ... Read More

An operating system (OS) is basically a collection of software that manages computer hardware resources and provides common services for computer programs. Operating system is a crucial component of the system software in a computer system.These are some few common services provided by an operating system −Program executionI/O operationsFile System manipulationCommunicationError DetectionResource AllocationProtectionA file represents a collection of related information. Computers may store files on the disk (secondary storage), for long-term storage purpose. Some Examples: magnetic tape, magnetic disk and optical disk drives like CD, DVD. They have its own properties like speed, capacity, data transfer rate and data access ... Read More