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Computer Network Articles
Page 112 of 122
Distributed Coordination Function (DCF)
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 MoreThe 802.11 MAC Sublayer Protocol
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 MoreMultiple Input Multiple Output (MIMO)
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 MoreUpgrade your computer for free to windows 10
People who have been using windows operating system usually encounter persistent messages to upgrade to Windows 10. The good news is that, upgrading to Windows 10 is now free. But in case of Apple, it allows its users to upgrade to newest operating system for free at any point. If users delay, they might land themselves in trouble as Windows is taking a very different approach.All those who have not upgraded their system to Windows 10 by June 29, 2016, they need to spend about $119. And those who consider, the cost of upgradation is more than they can handle. ...
Read MoreComplementary Code Keying (CCK)
Complementary Code Keying (CCK) is a modulation technique deployed in wireless local area networks (WLANs) that follow IEEE 802.11b specification. CCK came into use in 1999 whereby it replaced the Barker code in wireless networks. CCK helps in attaining data rates higher than 2 Mbps, though at the cost of shorter ranges.Features of CCKCCK is used in wireless LANs to attain theoretical maximum data rates of 11 Mbps.CCK is implemented for transmission in the radio frequency range (RF band) of 2.4GHz – 2.4835GHz.CCK includes a pair of codes called chipping sequences which are complementary to each other. In complementary codes, ...
Read MoreWhat is Rate Adaptation?
Rate adaptation is a criteria that determines the performance of IEEE 802.11 wireless networks, or WiFi. Rate adaptation allows transmission to be done at different rates within the wireless network, depending upon the network conditions.In wireless networks, the signal may be strong or weak. Through rate adaptation technique, the data transfer date can be changed depending upon the signal strength, i.e. when the signal is strong, high data rates are adopted, while low data rates are adopted during weak signals.Rate Adaptation AlgorithmsIn traditional rate adaptation algorithms, the lowest permissible data rate was selected for data transfer. Though this ensured that ...
Read MoreThe 802.11 Physical Layer
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.IEEE 802.11 ArchitectureThe physical layer architecture of IEEE 802.11 has the following components −Stations (STA) − Stations comprises of all devices and equipment that are connected to the wireless LAN. A station can be of two types −Wireless Access Point (WAP) − WAPs or simply access points (AP) are generally wireless routers that form ...
Read MoreWhat is Carrier Ethernet?
Carrier Ethernet is an application of Ethernet technology that allows network providers to offer Ethernet services to their customers and to use Ethernet technology. It enables Internet access and communication among local area networks (LANs) of business, academic, private and government organizations.The services and standards of carrier Ethernet have been defined by the Metro Ethernet Forum (MEF). MEF has also developed certification programs and it promotes the global adoption of carrier Ethernet.Carrier Ethernet versus EthernetThe primary attributes of Carrier Ethernet that differentiates it from Ethernet are −A carrier Ethernet network provides service to many organizations, while an Ethernet LAN renders ...
Read MoreRetrospective on Ethernet
Ethernet is a set of technologies and protocols that are used primarily in LANs. It was first standardized in the 1980s as IEEE 802.3 standard. It has been around since its inception and has seen different phases of development. A few other technologies have seen such consistency in usability.Advantages of EthernetEthernet is simple and reliable.It is economical since it mostly uses inexpensive twisted-pair cables.It is easily maintainable. It does not require installing any software, except for installing the network drivers.It is very less prone to failures. Once the network components are in place and correctly connected, it works perfectly.It can ...
Read More10-Gigabit Ethernet
In computer networks, 10-Gigabit Ethernet is the family of Ethernet technologies that achieve maximum rates up to 10 gigabits per second (10 Gbps). It is also known as 10GE, 10GbE or 10 GigE. It is defined by the IEEE 802.3ae-2002 standard.10GE is a thousand times faster than standard Ethernet and supports only full-duplex communication. Multimode fiber having 0.85μ frequency is used for medium distances and single-mode fiber having 1.5μ frequency is used for long distances.Varieties of Gigabit EthernetThe popular varieties of fast Ethernet are 1000Base-SX, 1000Base-LX, 1000BASE-T and 1000Base-CX.10GBase-SRDefined by IEEE 802.3ae standardUses fiber optic cablesMaximum segment length is 300 ...
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