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Traffic Indication Map
Traffic indication map (TIM) is a structure used in 802.11 wireless network management frames. The Traffic indication map information element is covered under section 7.3.2.6 of 802.11-1999 standard. The IEEE 802.11 standards use a bitmap to indicate to any sleeping listening stations that the Access Point (AP) has buffered data waiting for it. Because stations should listen to at least one beacon during the ''listen interval'', the AP periodically sends this bitmap in its beacons as an information element. The bit mask is called the Traffic Indication Map and consists of 2008 bits, each bit representing the Association ID (AID) of a station. However in most situations an AP only has data for a few stations, so only the portion of the bitmap representing those stations needs to be transmitted. Because the bitmap is never transmitted in its entirety, it is referred to as a ''virtual bitmap'', and the portion that is actually transmitted is referred to as a ''partial virtual bitmap' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IEEE 802
IEEE 802 is a family of Institute of Electrical and Electronics Engineers (IEEE) standards for local area networks (LAN), personal area network (PAN), and metropolitan area networks (MAN). The IEEE 802 LAN/MAN Standards Committee (LMSC) maintains these standards. The IEEE 802 family of standards has had twenty-four members, numbered 802.1 through 802.24, with a working group of the LMSC devoted to each. However, not all of these working groups are currently active. The IEEE 802 standards are restricted to computer networks carrying variable-size packets, unlike cell relay networks, for example, in which data is transmitted in short, uniformly sized units called cells. Isochronous signal networks, in which data is transmitted as a steady stream of octets, or groups of octets, at regular time intervals, are also outside the scope of the IEEE 802 standards. The number 802 has no significance: it was simply the next number in the sequence that the IEEE used for standards projects. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bitmap
In computing, a bitmap is a mapping from some domain (for example, a range of integers) to bits. It is also called a bit array A bit array (also known as bitmask, bit map, bit set, bit string, or bit vector) is an array data structure that compactly stores bits. It can be used to implement a simple set data structure. A bit array is effective at exploiting bit-level ... or bitmap index. As a noun, the term "bitmap" is very often used to refer to a particular bitmapping application: the pix-map, which refers to a map of pixels, where each one may store more than two colors, thus using more than one bit per pixel. In such a case, the domain in question is the array of pixels which constitute a digital graphic output device (a screen or monitor). In some contexts, the term ''bitmap'' implies one bit per pixel, whereas ''pixmap'' is used for images with multiple bits per pixel. A bitmap is a type of computer storage, memory organization or image file format used to store dig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Listening Station
A radio listening station (also: listening post, radio intercept station or wireless intercept station, W/T station for wireless telegraphy) is a facility used for military reconnaissance, especially telecommunications reconnaissance (also known as ''signals intelligence SIGINT'') by "intercepting" radio transmitter communications. In contrast to the original eavesdropping on an acoustic speech conversation, radio eavesdropping stations are used to eavesdrop on the information transmitted wirelessly using radio technology. For this purpose, highly sensitive radio receivers and suitable receiving antennas are used (see images). First World War After Heinrich Hertz (1857–1894) succeeded in 1886 as the first to generate electromagnetic waves in the ultra-short wave range, and Guglielmo Marconi (1874–1937) around 1900 was able to increase the range of his radio transmissions to hundreds of kilometers, thus radiotelegraphy technology was used in the First World War (1914–19 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beacon Frame
Beacon frame is one of the management frames in IEEE 802.11 based WLANs. It contains all the information about the network. Beacon frames are transmitted periodically, they serve to announce the presence of a wireless LAN and to synchronise the members of the service set. Beacon frames are transmitted by the access point (AP) in an infrastructure basic service set (BSS). In IBSS network beacon generation is distributed among the stations. For the 2.4 GHz spectrum, when having more than 15 SSIDs on non-overlapping channels (or more than 45 in total), beacon frames start to consume significant amount of air time and degrade performance even when most of the networks are idle. Components Beacon frames consist of an 802.11 MAC header, body and FCS. Some of the fields in the body are listed below. * * * * SSID * Supported rates * Frequency-hopping (FH) Parameter Set * Direct-Sequence (DS) Parameter Set * Contention-Free (CF) Parameter Set * IBSS Parameter Set * Traffic indi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bit Mask
In computer science, a mask or bitmask is data that is used for bitwise operations, particularly in a bit field. Using a mask, multiple bits in a byte, nibble, Word (computer architecture), word, etc. can be set either on or off, or inverted from on to off (or vice versa) in a single bitwise operation. An additional use of masking involves Predication (computer architecture), predication in vector processing, where the bitmask is used to select which element operations in the vector are to be executed (mask bit is enabled) and which are not (mask bit is clear). Common bitmask functions Masking bits to 1 To turn certain bits on, the Logical disjunction, bitwise OR operation can be used, following Logical disjunction#Bitwise operation, the principle that Y OR 1 = 1 and Y OR 0 = Y. Therefore, to make sure a bit is on, OR can be used with a 1. To leave a bit unchanged, OR is used with a 0. Example: Masking ''on'' the higher nibble (bits 4, 5, 6, 7) while leaving the lower nibble ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multicast
In computer networking, multicast is group communication where data transmission is addressed to a group of destination computers simultaneously. Multicast can be one-to-many or many-to-many distribution. Multicast should not be confused with physical layer point-to-multipoint communication. Group communication may either be application layer multicast or network-assisted multicast, where the latter makes it possible for the source to efficiently send to the group in a single transmission. Copies are automatically created in other network elements, such as routers, switches and cellular network base stations, but only to network segments that currently contain members of the group. Network assisted multicast may be implemented at the data link layer using one-to-many addressing and switching such as Ethernet multicast addressing, Asynchronous Transfer Mode (ATM), point-to-multipoint virtual circuits (P2MP) or InfiniBand multicast. Network-assisted multicast may also be impl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wireless Access Point
In computer networking, a wireless access point (WAP), or more generally just access point (AP), is a networking hardware device that allows other Wi-Fi devices to connect to a wired network. As a standalone device, the AP may have a wired connection to a router, but, in a wireless router, it can also be an integral component of the router itself. An AP is differentiated from a hotspot which is a physical location where Wi-Fi access is available. Connections An AP connects directly to a wired local area network, typically Ethernet, and the AP then provides wireless connections using wireless LAN technology, typically Wi-Fi, for other devices to use that wired connection. APs support the connection of multiple wireless devices through their one wired connection. Wireless data standards There are many wireless data standards that have been introduced for wireless access point and wireless router technology. New standards have been created to accommodate the increasing n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CSMA/CA
Carrier-sense multiple access with collision avoidance (CSMA/CA) in computer networking, is a network multiple access method in which carrier sensing is used, but nodes attempt to avoid collisions by beginning transmission only after the channel is sensed to be "idle". When they do transmit, nodes transmit their packet data in its entirety. It is particularly important for wireless networks, where the alternative with collision detection CSMA/CD, is not possible due to wireless transmitters desensing (turning off) their receivers during packet transmission. CSMA/CA is unreliable due to the hidden node problem. CSMA/CA is a protocol that operates in the data link layer (Layer 2) of the OSI model. Details Collision avoidance is used to improve the performance of the CSMA method by attempting to divide the channel somewhat equally among all transmitting nodes within the collision domain. # Carrier Sense: prior to transmitting, a node first listens to the shared medium (such as l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wi-Fi
Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio waves. These are the most widely used computer networks in the world, used globally in home and small office networks to link desktop and laptop computers, tablet computers, smartphones, smart TVs, printers, and smart speakers together and to a wireless router to connect them to the Internet, and in wireless access points in public places like coffee shops, hotels, libraries and airports to provide visitors with Internet access for their mobile devices. ''Wi-Fi'' is a trademark of the non-profit Wi-Fi Alliance, which restricts the use of the term ''Wi-Fi Certified'' to products that successfully complete interoperability certification testing. the Wi-Fi Alliance consisted of more than 800 companies from around the world. over 3.05 billion ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wi-Fi Alliance
The Wi-Fi Alliance is a non-profit organization that owns the Wi-Fi trademark. Manufacturers may use the trademark to brand products certified for Wi-Fi interoperability. History Early 802.11 products suffered from interoperability problems because the Institute of Electrical and Electronics Engineers (IEEE) had no provision for testing equipment for compliance with its standards. In 1999, pioneers of a new, higher-speed variant endorsed the IEEE 802.11b specification to form the Wireless Ethernet Compatibility Alliance (WECA) and branded the new technology Wi-Fi. The group of companies included 3Com, Aironet (acquired by Cisco), Harris Semiconductor (now Intersil), Lucent (was Alcatel-Lucent, then acquired by Nokia), Nokia and Symbol Technologies (now Zebra Technologies). The alliance lists Apple, Comcast, Samsung, Sony, LG, Intel, Dell, Broadcom, Cisco, Qualcomm, Motorola, Microsoft, Texas Instruments, and T-Mobile as key sponsors. The charter for this independent organizat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wireless Networking
A wireless network is a computer network that uses wireless data connections between network nodes. Wireless networking is a method by which homes, telecommunications networks and business installations avoid the costly process of introducing cables into a building, or as a connection between various equipment locations. Admin telecommunications networks are generally implemented and administered using radio communication. This implementation takes place at the physical level (layer) of the OSI model network structure. Examples of wireless networks include cell phone networks, wireless local area networks (WLANs), wireless sensor networks, satellite communication networks, and terrestrial microwave networks. History Wireless networks The first professional wireless network was developed under the brand ALOHAnet in 1969 at the University of Hawaii and became operational in June 1971. The first commercial wireless network was the WaveLAN product family, developed by NCR i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
