IEEE 802.11-2020: Collision Avoidance in Wireless Networks

Computers using CSMA/CA methods to avoid collision in wireless networks, adhering to IEEE 802.11-2020.

IEEE 802.11-2020: Wireless LAN Medium Access Control (MAC) And Physical Layer (PHY) Specifications has become the dominant solution for Wireless Local Area Networks (WLANs) due to its high performance, low cost, and easiness in deployment. IEEE 802.11 is used in most home and office networks to allow computers, printers, smartphones, and other devices to communicate with each other and access the Internet wirelessly.  

Why Do We Need Collision Avoidance in Networks?

Wi-Fi devices share the same medium: radio frequency (RF). In any given RF region that contains multiple wireless devices, only one device can transmit data a time (although various devices may listen at the same time). This requires that all other devices connected to the same endpoint or access point (AP) listen to the transmission to avoid collisions. Since many devices are connected to one single shared stream of transmission, collisions are likely to occur. Collision avoidance divides the wireless channels equally among transmitting nodes within the collision domain. It is supplemented by exchanging requests to send a packet. Nodes within senders and receivers are alerted not to transmit for the duration of main transmissions. Wireless networks must avoid collisions to ensure packets reach their destination.

What Are CSMA/CA, RTS/CTS, and MBCA?

If a collision is detected in wired IEEE 802.3-2022 technologies, packets can be present, unlike in wireless technologies, where there is no way to detect a collision over the air. To ensure there is no collision in wireless local area networks (WLANs), only one device in the RF region can transmit at any time. Since only a single device in the RF region may transmit at a time, 802.11 WLANs have methods of ensuring only a single device in the RF region transmits data at a time. These methods in IEEE 802.11-2020 include CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance), RTS/CTS (Request To Send/Clear To Send), and MBCA (Mesh Beacon Collision Avoidance).

Wireless technology and IEEE 802.11-2020 concept showing collision avoidance in wireless network,

What Is CSMA/CA?

The Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol is designed to reduce the collision probability between multiple movable stations (STAs) accessing a medium, at the point where collisions would most likely occur. In CSMA/CA, the moment a node receives a packet intended for sending, CSMA/CA listens to the broadcast channel for a pre-specified time frame to determine if another node is broadcasting on the channel inside the wireless range. If the broadcast channel is detected as “idle,” the node can then start transmitting the data packet. It is this moment just after the medium becomes idle following a busy medium (as indicated by the carrier sensing function) when the highest probability of a collision exists. This is because multiple wireless network stations could have been waiting for the medium to become available again. This is the situation that necessitates a random back off procedure to resolve medium contention conflicts.

What Is the Difference Between CSMA/CA VS CSMA/CD?

CSMA (Carrier Sense Multiple Access) is a network protocol for carrier transmission that operates in the Medium Access Control (MAC) layer that is used to control the flow of data in a transmission media so that packets do not get lost and data integrity is maintained. CSMA operates by sensing the state of the medium in order to prevent or receiver from collision. There are two modifications to CSMA: CSMA/CA and CMSA/CD.

  1. CSMA/CA prevents collisions prior to their occurrence. It initially transmitting the intent to send the data and once an acknowledgement is received, the sender send the data. CSMA/C is part of IEEE 802.11-2020 and is used in wireless networks.
  2. CSMA/CD (Carrier Sense Multiple Access/Collision Detection) deals with collisions after their occurrence, resending the data frame in case a conflict occurs during transmission. CSMA/CD is part of the IEEE 802.3-2022 standard and is used in wired networks.

What Is RTS/CTS?

Request to Send/Clear To Send (RTS/CTS) is a control frame employed in the medium access control (MAC) layer protocol IEEE 802.11-2020 RTS/CTS. It is an additional method to implement virtual carrier sensing in CSMA/CA. The IEEE 802.11-2020 protocol uses the concept of Multiple Access with Collision Avoidance (MACA) in wireless networks. The RTS mechanism aims to reduce frame collisions introduced by the hidden terminal problem. RTS frame is sent by the transmitter prior to transmission of the actual data frame.

What Is MBCA?

Mesh beacon collision avoidance (MBCA) mitigates collisions of beacon frames among hidden nodes. MBCA is composed of beacon timing advertisements, TBTT (target beacon transmission time) selection, and TBTT adjustment. Mesh STAs use the mesh beacon collision avoidance (MBCA) protocol to detect and mitigate collisions among Beacon frames transmitted by other network communication stations (including mesh STAs, IBSS APs, and IBSS STAs) on the same channel within the range of 2 hops. MBCA mitigates hidden node problems with respect to Beacon frames

To avoid collision in wireless local area networks, IEEE 802.11-2020 covers specifications, methods, and procedures.

Teens using smartphones in WLANs, adhering to IEEE 802.11-2020.

What Is IEEE 802.11-2020?

IEEE 802.11-2020 is Part 11 of the Institute of Electrical and Electronics Engineers (IEEE) 802 Series: Telecommunications And Information Exchange Between Systems. IEEE 802.11-2020 defines one medium access control (MAC) and several physical layer (PHY) specifications for local area networks (LAN) and metropolitan area networks (MAN).

  • Medium access control (MAC): a sublayer of the data link layer of the open system interconnections (OSI) reference model for data transmission. It is responsible for flow control and multiplexing for transmission medium, making it possible for several terminals or network nodes to communicate with multiple access network that incorporates a shared medium (e.g., Ethernet).
  • Several physical layer (PHY): the first and lowest layer (layer 1) in the seven-layer OSI model of computer networking, and in wireless systems it is the layer that sends and receives radio frequency signals. The physical layer is the only layer in the OSI model that plays the role of interacting with actual hardware, transmission and signaling mechanisms.
  • Local area networks (LAN): a collection of devices (e.g. computers) connected together in one physical location, such as a building, office, or home, that share a common communication line or wireless link to a server within a distinct geographic area. A LAN can be small or large, ranging from a home network with one user to an enterprise network with thousands of users and devices in an office or school.
  • Metropolitan area networks (MAN): a computer network that connects computers within a metropolitan area, which could be a single large city, multiple cities and towns, or any given large area with multiple buildings. It typically is a combined networked of multiple organizations, instead of being managed by a single organization. A MAN is larger than a local area network (LAN) but smaller than a wide area network (WAN), and both MANs and WANs are made up of interconnected LANs.

The standard describes the functions and services required by a device to operate within independent, personal, and infrastructure networks, as well as the aspects of device mobility (transition) within those networks. IEEE 802.11-2020 defines functions and procedures aiding network discovery and selection by devices, information transfer from external networks using quality of service mapping, and a general mechanism for the provision of emergency services. Its purpose is to provide wireless connectivity for fixed, portable, and moving stations within a local area.

IEEE 802.11-2020: Wireless LAN Medium Access Control (MAC) And Physical Layer (PHY) Specifications is available on the ANSI Webstore.

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