In communications, a channel access method is used to share a communications channel or physical communications medium between multiple users.

Examples of channel access methods:

• Frequency division multiple access (FDMA)
• Time-division multiple access (TDMA)
• Code division multiple access (CDMA)
• Frequency-hopping spread spectrum (FHSS)
• Space division multiple access (SDMA)
• Wavelength division multiple access (WDMA)
• Carrier sense multiple access with collision detection (CSMA/CD)

In the OSI seven layer model, channel access methods are typically placed at layer 1, the physical layer.

Where these methods are used for dividing forward and reverse communication channels, they are known as duplexing methods, such as:

• 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.

See also:

• modulation
• spread spectrum
• Ethernet