Channel access method

In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminals connected to the same transmission medium to transmit over it and to share its capacity. Examples of shared physical media are wireless networks, bus networks, ring networks and point-to-point links operating in half-duplex mode. A channel access method is based on multiplexing, that allows several data streams or signals to share the same communication channel or transmission medium. In this context, multiplexing is provided by the physical layer. A channel access method may also be a part of the multiple access protocol and control mechanism, also known as medium access control (MAC). Medium access control deals with issues such as addressing, assigning multiplex channels to different users and avoiding collisions. Media access control is a sub-layer in the data link layer of the OSI model and a component of the link layer of the TCP/IP model. Several ways of categorizing multiple-access schemes and protocols have been used in the literature. For example, Daniel Minoli (2009) identifies five principal types of multiple-access schemes: FDMA, TDMA, CDMA, SDMA, and Random access. R. Rom and M. Sidi (1990) categorize the protocols into Conflict-free access protocols, Aloha protocols, and Carrier Sensing protocols. The Telecommunications Handbook (Terplan and Morreale, 2000) identifies the following MAC categories: Fixed assigned: TDMA, FDMA+WDMA, CDMA, SDMA Demand assigned (DA) Reservation: DA/TDMA, DA/FDMA+DA/WDMA, DA/CDMA, DA/SDMA Polling: Generalized polling, Distributed polling, Token Passing, Implicit polling, Slotted access Random access (RA): Pure RA (ALOHA, GRA), Adaptive RA (TRA), CSMA, CSMA/CD, CSMA/CA Channel access schemes generally fall into the following categories. The frequency-division multiple access (FDMA) channel-access scheme is the most standard analog system, based on the frequency-division multiplexing (FDM) scheme, which provides different frequency bands to different data streams.