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access method

Access procedures are all procedures that organize the access of communication devices and data stations to a shared transmission medium. The transmission medium can be the physical medium of a local network, but also a radio channel or a logical channel. In the case of access procedures, a distinction is made between partnership-regulated and distributed procedures.

Access procedures in local area networks (LAN)

In local area networks (LAN), access procedures regulate access to the transmission medium. It is a kind of agreement between the stations which enables them to determine the station authorized to transmit. Since all stations connected to the transmission medium can theoretically use it simultaneously, access regulation is required.

Media access methods are classified as deterministic, nondeterministic, and centralized and are located at the second layer of the OSI reference model. Deterministic access methods are token methods where one station can transmit in accordance with the other stations. Stochastic access methods operate randomly. In this method, individual stations compete for the right to transmit. These are collision methods. When multiple stations transmit at the same time, collisions may occur, which are resolved with a remediation strategy. Centralized access methods are reservation methods in which a transmission request must be registered and the central control station reserves a slot or container for transmission.

Deterministic and non-deterministic access procedures

Deterministic and non-deterministic access procedures

Layer 1 forms a logical layer for media access, which in most procedures is assigned to only one transmitting station at a time. Access methods are divided into selection, reservation, random, and a combination of these methods. Standardized access methods are the CSMA/CD access method, Token Ring, Slotted Ring, Token Bus, Demand-Priority method and the DQDB access method, Queued Packet and Synchronous Exchange (QPSX).

Access methods in radio networks (WLAN)

In radio-based communication systems, the limited resources can be improved by various radio-based multiple access methods. These procedures are used to control access from one or more mobile or stationary receiving stations to the base stations and thus to the radio channels. Possible improvement scenarios include radio cell reduction, multiple use of carrier frequencies, and dynamic multiple access. Possible techniques include: Time Division Multiple Access (TDMA), FDMA (Frequency), CDMA(Code), SDMA ( Space), Spread Spectrum Multiple Access (SSMA), Orthogonal Frequency Division Multiple Access (OFDMA) and Scalable Orthogonal Frequency Division Multiple Access (SOFDMA).

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Englisch: access method
Updated at: 25.12.2020
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