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Articles by Moumita
Page 4 of 12
What is ad-hoc network?
An ad hoc network is a spontaneously formed network where devices connect and communicate with each other directly without requiring a central infrastructure. The term "ad hoc" is Latin for "for this, " implying an improvised or temporary arrangement. Ad hoc networks are primarily wireless local area networks (WLANs) where devices communicate peer-to-peer instead of relying on base stations or access points. Each device participates in routing by determining optimal paths using routing algorithms and forwarding data to other devices through these routes. Ad Hoc Network: Direct Device Communication ...
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 Architecture The physical layer architecture of IEEE 802.11 has the following components − Stations (STA) − Stations comprise all devices and equipment that are connected to the wireless LAN. A station can be of two types − Wireless Access Point (WAP) − WAPs or ...
Read MoreWhat is Rate Adaptation?
Rate adaptation is a technique used in IEEE 802.11 wireless networks (WiFi) that dynamically adjusts the data transmission rate based on current network conditions. This mechanism enables optimal performance by selecting the most appropriate data rate for the prevailing signal quality. In wireless networks, signal strength varies due to factors like distance, interference, and obstacles. Rate adaptation responds to these changes by increasing data rates when signal conditions are favorable and reducing them when conditions deteriorate, ensuring reliable communication while maximizing throughput. Rate Adaptation Process Strong ...
Read MoreComplementary Code Keying (CCK)
Complementary Code Keying (CCK) is a modulation technique deployed in wireless local area networks (WLANs) that follow the 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. CCK uses mathematically related code pairs called complementary sequences to encode data more efficiently than its predecessor. This technique enabled the significant speed improvements that made 802.11b networks commercially viable for business applications. How CCK Works CCK operates by using shorter chipping sequences of ...
Read MoreArbitration Inter-Frame Spacing (AIFS)
Arbitration Inter-Frame Spacing (AIFS) is a quality of service mechanism used in IEEE 802.11e WLAN standard (Wi-Fi) to provide differentiated channel access at the medium access control (MAC) layer. It determines the time interval that a station must wait before transmitting, prioritizing stations based on their Access Category (AC). How AIFS Works In wireless communication, collision detection is difficult due to the hidden node problem and signal fading. Therefore, collision avoidance schemes are essential when multiple stations compete for channel access. AIFS assigns different waiting periods to frames based on their priority level, ensuring that time-sensitive traffic like ...
Read MoreRate Anomaly in CSMA/CA
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) is a network protocol for carrier transmission that operates in the Medium Access Control (MAC) layer. CSMA/CA prevents collisions prior to their occurrence and is ideally used in wireless communications. Rate anomaly occurs when the performance of a high-speed station is impaired due to a low-speed station, thus reducing the average throughput of the entire wireless network. This phenomenon significantly affects network efficiency in mixed-rate environments. How Rate Anomaly Occurs The CSMA/CA protocol allows each station to send a single frame at a time. Before sending a frame, the ...
Read MoreExtended Inter-Frame Spacing (EIFS)
Extended Inter-Frame Spacing (EIFS) is a waiting period used in the MAC layer of IEEE 802.11-based wireless local area network (WLAN) standard. It is an additional waiting period used in addition to the mandatory DIFS technique when frames are corrupted or cannot be properly decoded. DIFS (Distributed Coordination Function Inter-Frame Spacing) is inserted before sending frames to avoid collisions in areas where Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) is used. EIFS is specifically used when a station receives erroneous or corrupted frames that it cannot decode properly. How EIFS Works In normal frame delivery, the ...
Read MoreTransmission opportunity (TXOP)
Transmit opportunity (TXOP) is a MAC layer feature used in IEEE 802.11-based wireless local area networks (WLANs). TXOP defines the time duration for which a station can send frames after it has gained contention for the transmission medium. By providing this contention-free time period, TXOP aims to increase the throughput of high priority data, such as voice and video. TXOP is available in Quality of Service (QoS) as part of Enhanced Distributed Channel Access (EDCA), which provides differentiated access to the wireless medium based on traffic categories. TXOP Time Allocation by Access Category ...
Read MoreInter – frame spaces (RIFS, SIFS, PIFS, DIFS, AIFS, EIFS)
Inter-frame spaces (IFS) are waiting periods between transmission of frames in the medium access control (MAC) sublayer where carrier-sense multiple access with collision avoidance (CSMA/CA) is used. These are techniques used to prevent collisions as defined in IEEE 802.11-based WLAN standard (Wi-Fi). IFS is the time period between completion of the transmission of the last frame and starting transmission of the next frame, apart from the variable back-off period. Different types of IFS provide priority mechanisms, with shorter durations indicating higher priority access to the wireless medium. Inter-frame Spaces Priority Order Higher ...
Read MoreThe 802.11 Frame Structure
The IEEE 802.11 standard defines the architecture and specifications of wireless local area networks (WLANs). WLAN or WiFi uses high frequency radio waves instead of cables for connecting devices in a 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 Structure of IEEE 802.11 The main fields of a frame in WLANs as laid down ...
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