Multiple Access with Collision Avoidance (MACA) is a medium access control (MAC) layer protocol used in wireless networks, with a view to solve the hidden terminal problem. It also provides solution to the exposed terminal problem. The MAC layer protocol IEEE 802.11 RTS/CTS has been adopted from MACA.Working PrincipleThe MACA protocol works with the condition that the stations are synchronized and frame sizes and data speed are the same. It involves transmission of two frames called RTS and CTS prior to data transmission. RTS stands for Request to Send and CTS stands for Clear to Send.Let us consider that a ... Read More

In wireless LANs ( wireless local area networks), the hidden terminal problem is a transmission problem that arises when two or more stations who are out of range of each other transmit simultaneously to a common recipient. This is prevalent in decentralised systems where there aren’t any entity for controlling transmissions. This occurs when a station is visible from a wireless access point (AP), but is hidden from other stations that communicate with the AP.Problem IllustrationSuppose that there are three stations labelled STA, STB, and STC, where STA and STC are transmitting while STB is receiving. The stations are in ... Read More

In wireless LANs (wireless local area networks), the exposed terminal problem is a transmission problem that arises when a transmitting station is prevented from sending frames due to interference with another transmitting station. This is prevalent in decentralised systems where there aren’t any entity for controlling transmissions. This occurs when a station is visible from a wireless access point (AP), but not from other stations that communicate with the AP.Problem IllustrationSuppose that there are four stations labelled STA, STB, STC, and STD, where STB and STC are transmitters while STA and STD are receivers at some slot of time. The ... Read More

Wireless LANs refer to LANs (Local Area Networks) that use high frequency radio waves instead of cables for connecting the devices. It can be conceived as a set of laptops and other wireless devices communicating by radio signals. Users connected by WLANs can move around within the area of network coverage. Most WLANs are based upon the standard IEEE 802.11 or WiFi.Configuration of Wireless LANsEach station in a Wireless LAN has a wireless network interface controller. A station can be of two categories −Wireless Access Point (WAP) − WAPs or simply access points (AP) are generally wireless routers that form ... Read More

Adaptive Tree Walk Protocol is a technique for transmitting data over shared channels that combines the advantages of collision based protocols and collision free protocols.In computer networks, when more than one station tries to transmit simultaneously via a shared channel, the transmitted data is garbled, an event called collision. In collision based protocols like ALOHA, all stations are permitted to transmit a frame without trying to detect whether the transmission channel is idle or busy. This works very good under light loads. Under heavy loads, collision free protocols are suitable, since channel access is resolved in the contention period that ... Read More

Limited Contention Protocols are the media access control (MAC) protocols that combines the advantages of collision based protocols and collision free protocols. They behave like slotted ALOHA under light loads and bitmap protocols under heavy loads.ConceptIn computer networks, when more than one station tries to transmit simultaneously via a shared channel, the transmitted data is garbled, an event called collision. In collision based protocols like ALOHA, all stations are permitted to transmit a frame without trying to detect whether the transmission channel is idle or busy. In slotted ALOHA, the shared channel is divided into a number of discrete time ... Read More

Binary Countdown Protocol is a collision-free protocol that operates in the Medium Access Control (MAC) layer of the OSI model. In computer networks, when more than one station tries to transmit simultaneously via a shared channel, the transmitted data is garbled, an event called collision. Collision-free protocols resolves channel access while the stations are contending for the shared channel, thus eliminating any possibilities of collisions.Working Principle of Binary CountdownIn a binary countdown protocol, each station is assigned a binary address. The binary addresses are bit strings of equal lengths. When a station wants to transmit, it broadcasts its address to ... Read More

Resilient Packet Ring (RPR), standardized as IEEE 802.17, is a protocol standard for data transmission over fiber optic ring networks, that operates in the Media Access Control (MAC) layer of the Open Systems Interconnection (OSI) model. It provides a packet based transmission facility, with the aim of improving efficiency of Ethernet and IP services. RPR provides improved bandwidth utilization and throughput, greater speed of deployment, and optimized equipment and operational costs.Working PrincipleThe stations in a RPR are connected by dual counter rotating fiber optic rings called ringlets. Transmission occurs along both the rings. This helps to utilize the total available ... Read More

Fiber Distributed Data Interface (FDDI) is a set of ANSI and ISO standards for transmission of data in local area network (LAN) over fiber optic cables. It is applicable in large LANs that can extend up to 200 kilometers in diameter. Features FDDI uses optical fiber as its physical medium. It operates in the physical and medium access control (MAC layer) of the Open Systems Interconnection (OSI) network model. It provides high ... Read More

Token RingToken ring (IEEE 802.5) is a communication protocol in a local area network (LAN) where all stations are connected in a ring topology and pass one or more tokens for channel acquisition. A token is a special frame of 3 bytes that circulates along the ring of stations. A station can send data frames only if it holds a token. The tokens are released on successful receipt of the data frame.Token Passing Mechanism in Token RingIf a station has a frame to transmit when it receives a token, it sends the frame and then passes the token to the ... Read More