Wireless Networks- Lecture 8:WLAN Frames Types & WLAN Connectivity

MAC
To maintain some safety in data communications, certain rules and guidelines must be established and followed. This is especially important in wireless communications because of the nature of the medium used for the
communications—air or space. The rules and guidelines are specified at different layers of the OSI model.
MAC is a sublayer of the OSI’s Data Link layer. The MAC sublayer is basically responsible for providing addressing and medium access control mechanisms that make it possible for several nodes to communicate in a network.
The MAC functions are used to control and manage access to the transmission medium in a communications system.
Controlling the access of stations plugged into a wired Ethernet LAN (IEEE 802.3) is relatively simple because of the use of cables. All nodes plugged into the same network can easily sense the presence or absence of an electric current in their cables. The electric current here implies the data transmission. To coordinate access to the LAN medium, LAN stations use Carrier Sense Multiple Access with Collision Detection (CSMA/CD). The key word here is “detection”.
The rules that govern the IEEE 802.11 WLANs can not easily use same method for managing access to the shared medium used in wired LANs, one reason behind this is the absence of physical wires.
The Stations in a wireless network cannot always be guaranteed to be within earshot of each other so that they can hear (or detect) when the other STAs are transmitting. This phenomena is known as the “hidden node” problem in RF communications. Furthermore, the transmission may not even be destined for the hidden node, but it still needs to use the common transmission medium shared by all the nodes.