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Hidden Node Problem
In wireless networking, the hidden node problem or hidden terminal problem occurs when a Node (networking), node can communicate with a wireless access point (AP), but cannot directly communicate with other nodes that are communicating with that AP. This leads to difficulties in medium access control sublayer since multiple nodes can send data packets to the AP simultaneously, which creates interference at the AP resulting in no packet getting through. Although some loss of packets is normal in wireless networking, and the higher layers will resend them, if one of the nodes is transferring a lot of large packets over a long period, the other node may get very little goodput. Practical protocol solutions exist to the hidden node problem. For example, IEEE 802.11 RTS/CTS, Request To Send/Clear To Send (RTS/CTS) mechanisms where nodes send short packets to request permission of the access point to send longer data packets. As responses from the AP are seen by all the nodes, the node ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wifi Hidden Station Problem
Wi-Fi () is a family of wireless network protocols based on the IEEE 802.11 family of standards, which are commonly used for Wireless LAN, 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, used globally in small office/home office, home and small office networks to link devices and to provide Internet access with wireless routers and wireless access points in public places such as coffee shops, restaurants, hotels, libraries, and airports. ''Wi-Fi'' is a trademark of the Wi-Fi Alliance, which restricts the use of the term "''Wi-Fi Certified''" to products that successfully complete Interoperability Solutions for European Public Administrations, interoperability certification testing. Non-compliant hardware is simply referred to as WLAN, and it may or may not work with "''Wi-Fi Certified''" devices. the Wi-Fi Alliance consisted of more than 800 companies from ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
VDM Verlag
Omniscriptum Publishing Group, formerly known as VDM Verlag Dr. Müller, is a German publishing group headquartered in Riga, Latvia. Founded in 2002 in Düsseldorf, its book production is based on print-to-order technology. The company publishes theses, research notes, and dissertations through its e-commerce bookstores. OmniScriptum is designated as non-academic by the Norwegian Scientific Index, and its subsidiary Lambert Academic Publishing has been described as a predatory vanity press which does "not apply the basic standards of academic publishing such as peer-review, editorial or proof-reading processes." The company also offers print-to order publishing for fiction authors. It previously specialized in publishing and selling Wikipedia articles, but has stated that the practice of publishing Wikipedia content ended in 2013. History The group's first publishing house was founded in Düsseldorf in 2002 by Wolfgang Philipp Müller and relocated to Saarbrücken in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wireless LAN
A wireless LAN (WLAN) is a wireless computer network that links two or more devices using wireless communication to form a local area network (LAN) within a limited area such as a home, school, computer laboratory, campus, or office building. This gives users the ability to move around within the area and remain connected to the network. Through a Gateway (telecommunications), gateway, a WLAN can also provide a connection to the wider Internet. Wireless LANs based on the IEEE 802.11 standards are the most widely used computer networks in the world. These are commonly called Wi-Fi, which is a trademark belonging to the Wi-Fi Alliance. They are used for home and small office networks that link together laptop computers, printer (computing), printers, smartphones, Web TVs and gaming devices through a Wireless router, wireless network router, which in turn may link them to the Internet. Hotspot (Wi-Fi), Hotspots provided by routers at restaurants, coffee shops, hotels, libraries, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Point Coordination Function
Point Coordination Function (PCF) is a media access control (MAC) technique used in IEEE 802.11 based WLANs, including Wi-Fi. It resides in a point coordinator also known as access point (AP), to coordinate the communication within the network. The AP waits for PIFS duration rather than DIFS duration to grasp the channel. PIFS is less than DIFS duration and hence the point coordinator always has the priority to access the channel. The PCF is located directly above the distributed coordination function (DCF), in the IEEE 802.11 MAC Architecture. Channel access in PCF mode is centralized and hence the point coordinator sends CF-Poll frame to the PCF capable station to permit it to transmit a frame. In case the polled station does not have any frames to send, then it must transmit null frame. Due to the priority of PCF over DCF, stations that only use DCF might not gain access to the medium. To prevent this, a repetition interval has been designed to cover both (Contention free) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Exposed Node Problem
In wireless networks, the exposed node problem occurs when a node is prevented from sending packets to other nodes because of co-channel interference with a neighboring transmitter. Consider an example of four nodes labeled R1, S1, S2, and R2, where the two receivers (R1, R2) are out of range of each other, yet the two transmitters (S1, S2) in the middle are in range of each other. Here, if a transmission between S1 and R1 is taking place, node S2 is prevented from transmitting to R2 as it concludes after carrier sense that it will interfere with the transmission by its neighbor S1. However note that R2 could still receive the transmission of S2 without interference because it is out of range of S1. IEEE 802.11 RTS/CTS mechanism helps to solve this problem only if the nodes are synchronized and packet sizes and data rates are the same for both the transmitting nodes. When a node hears an RTS from a neighboring node, but not the corresponding CTS, that node can deduce that it i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cellular Network
A cellular network or mobile network is a telecommunications network where the link to and from end nodes is wireless network, wireless and the network is distributed over land areas called ''cells'', each served by at least one fixed-location transceiver (such as a base station). These base stations provide the cell with the network coverage which can be used for transmission of voice, data, and other types of content via radio waves. Each cell's coverage area is determined by factors such as the power of the transceiver, the terrain, and the frequency band being used. A cell typically uses a different set of frequencies from neighboring cells, to avoid interference and provide guaranteed service quality within each cell. When joined together, these cells provide radio coverage over a wide geographic area. This enables numerous Mobile device, devices, including mobile phones, Tablet computer, tablets, laptops equipped with mobile broadband modems, and Wearable technology, wea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Token Passing
On a local area network, token passing is a channel access method where a packet called a ''token'' is passed between nodes to authorize that node to communicate. In contrast to polling access methods, there is no pre-defined "master" node. The most well-known examples are IBM Token Ring and ARCNET, but there were a range of others, including FDDI (Fiber Distributed Data Interface), which was popular in the early to mid 1990s. Token passing schemes degrade deterministically under load, which is a key reason why they were popular for industrial control LANs such as MAP, (Manufacturing Automation Protocol). The advantage over contention based channel access (such as the CSMA/CD of early Ethernet), is that collisions are eliminated, and that the channel bandwidth can be fully utilized without idle time when demand is heavy. The disadvantage is that even when demand is light, a station wishing to transmit must wait for the token, increasing latency. Some types of token passing s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polling (computer Science)
Polling, or interrogation, refers to actively sampling the status of an external device by a client program as a synchronous activity. Polling is most often used in terms of input/output (), and is also referred to as polled or software-driven . A good example of hardware implementation is a watchdog timer. Description Polling is the process where the computer or controlling device waits for an external device to check for its readiness or state, often with low-level hardware. For example, when a printer is connected via a parallel port, the computer waits until the printer has received the next character. These processes can be as minute as only reading one bit. This is sometimes used synonymously with ' busy-wait' polling. In this situation, when an operation is required, the computer does nothing other than check the status of the device until it is ready, at which point the device is accessed. In other words, the computer waits until the device is ready. Polling also ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Point-to-point (telecommunications)
In telecommunications, a point-to-point connection refers to a communications connection between two communication endpoints or nodes. An example is a telephone call, in which one telephone is connected with one other, and what is said by one caller can only be heard by the other. This is contrasted with a ''point-to-multipoint'' or ''broadcast'' connection, in which many nodes can receive information transmitted by one node. Other examples of point-to-point communications links are leased lines and microwave radio relay. The term is also used in computer networking and computer architecture to refer to a wire or other connection that links only two computers or circuits, as opposed to other network topologies such as buses or crossbar switches which can connect many communications devices. ''Point-to-point'' is sometimes abbreviated as ''P2P''. This usage of ''P2P'' is distinct from ''P2P'' meaning ''peer-to-peer'' in the context of file sharing networks or other data- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Directional Antenna
A directional antenna or beam antenna is an antenna that radiates or receives greater radio wave power in specific directions. Directional antennas can radiate radio waves in beams, when greater concentration of radiation in a certain direction is desired, or in receiving antennas receive radio waves from one specific direction only. This can increase the power transmitted to receivers in that direction, or reduce interference from unwanted sources. This contrasts with omnidirectional antennas such as dipole antennas which radiate radio waves over a wide angle, or receive from a wide angle. The extent to which an antenna's angular distribution of radiated power, its radiation pattern, is concentrated in one direction is measured by a parameter called antenna gain. A high-gain antenna (HGA) is a directional antenna with a focused, narrow beam width, permitting more precise targeting of the radio signals. Most commonly referred to during space missions, these antennas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
WiFi
Wi-Fi () is a family of wireless network protocols based on the IEEE 802.11 family of standards, which are commonly used for Wireless LAN, 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, used globally in small office/home office, home and small office networks to link devices and to provide Internet access with wireless routers and wireless access points in public places such as coffee shops, restaurants, hotels, libraries, and airports. ''Wi-Fi'' is a trademark of the Wi-Fi Alliance, which restricts the use of the term "''Wi-Fi Certified''" to products that successfully complete Interoperability Solutions for European Public Administrations, interoperability certification testing. Non-compliant hardware is simply referred to as WLAN, and it may or may not work with "''Wi-Fi Certified''" devices. the Wi-Fi Alliance consisted of more than 800 companies from ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CSMA/CA
Carrier-sense multiple access with collision avoidance (CSMA/CA) in computer networking, is a link layer multiple access method in which carrier sensing is used. Under CSMA/CA, nodes attempt to avoid collisions by beginning transmission only after the channel is sensed to have no traffic. When they do transmit, nodes transmit frames in their entirety. This technique is primarily used in wireless networks, where the alternative with collision detection CSMA/CD is not possible due to wireless transmitters de-sensing (turning off) their receivers during packet transmission. CSMA/CA is unreliable due to the hidden node problem. 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 listening for wireless signals in a wireless network) to determine whe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
