In communications, a channel access method is used to share a communications channel or physical communications medium between multiple users. The term communications is used in a number of disciplines: Communications, also known as communication studies is the academic discipline which studies communication. ... A Communications channel (or channel for short), models the medium through which information is transmitted from a sender (or transmitter) to a receiver. ...

Examples of channel access methods:

• Frequency division multiple access (FDMA)
• Time-division multiple access (TDMA)
• Spread spectrum multiple access (SSMA)
  • Direct-sequence spread spectrum (DS-SS)
  • Frequency-hopping spread spectrum (FH-SS)
  • Code division multiple access (CDMA) - the overarching form of DS-SS and FH-SS
• Space division multiple access (SDMA)
• Wavelength division multiple access (WDMA)
• Carrier Sense Multiple Access
  • Carrier sense multiple access with collision detection (CSMA/CD)
  • Carrier sense multiple access with collision avoidance (CSMA/CA)
  • Carrier sense multiple access with collision avoidance and Resolution using Priorities (CSMA/CARP)

Where these methods are used for dividing forward and reverse communication channels, they are known as duplexing methods, such as: FDMA, or frequency-division multiple access, is the oldest and most important of the three main ways for multiple radio transmitters to share the radio spectrum. ... Time Division Multiple Access (TDMA) is a technology for shared medium (usually radio) networks. ... Spread-spectrum telecommunications is a technique in which a signal is transmitted in a bandwidth considerably greater than the frequency content of the original information. ... In telecommunication, the term direct-sequence spread spectrum has the following meanings: A system (a) for generating spread-spectrum transmissions by phase-modulating a sine wave pseudorandomly with a continuous string of pseudonoise code symbols, each of duration much smaller than a bit and (b) that may be time-gated... Frequency-hopping spread spectrum (FHSS) is a spread-spectrum method of transmitting signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. ... Code division multiple access (CDMA) is a method of multiple access that does not divide up the channel by time (as in TDMA), or frequency (as in FDMA), but instead encodes data with a certain code associated with a channel and uses the constructive interference properties of the signal medium... SDMA or space-division multiple access is a channel access method which enables the use of the same frequency (for instance on GSM systems) at the same time in different spaces (cells). ... In telecommunications wavelength division multiplexing (WDM) is a technology which multiplexes several optical carrier signals on a single optical fibre by using different wavelengths (colours) of laser light to carry different signals. ... Carrier Sense Multiple Access (CSMA) is a non-deterministic Media Access Control (MAC) protocol in which a node verifies the absence of other traffic before transmitting on a shared physical medium, such as an electrical bus, or a band of electromagnetic spectrum. ... In computer networking, Carrier Sense Multiple Access With Collision Detection (CSMA/CD) is a network control protocol in which (a) a carrier sensing scheme is used and (b) a transmitting data station that detects another signal while transmitting a frame, stops transmitting that frame, transmits a jam signal, and then... In computer networking, Carrier Sense Multiple Access With Collision Avoidance (CSMA/CA) is a network control protocol in which: a carrier sensing scheme is used, a data station that intends to transmit sends a jam signal after waiting a sufficient time for all stations to receive the jam signal, the... The introduction of this article does not provide enough context for readers unfamiliar with the subject. ... Duplex is the having of two principal elements or parts. ...

• Time division duplex (TDD)
• Frequency division duplex (FDD)

Note that hybrids of these techniques can be and frequently are used: for example, GSM combines the use of frequency division duplex to prevent interference between outward and return signals, with TDMA to allow multiple handsets to work in a single cell. In telecommunications, duplex means two-way when referring to communications channels. ... Duplex is the having of two principal elements or parts. ... In biology, hybrid has three meanings. ... GSM (Global System for Mobile Communications) is the most popular standard for mobile phones in the world. ...

In the OSI seven layer model, channel access methods are typically placed at layer 1, the physical layer. The physical layer is level one in the seven level OSI model of computer networking. ...

See also

• Modulation