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CSMA (Carrier Sense Multiple Access):

  • Concept: CSMA is a protocol where each node listens to the channel before transmitting. If the channel is sensed to be idle, the node transmits. If the channel is busy, the node waits for a random backoff time and retries.
  • Application: CSMA is used in Ethernet LANs (Local Area Networks) to regulate access to the shared communication medium.

2. CSMA/CD (Carrier Sense Multiple Access with Collision Detection):

  • Concept: CSMA/CD is an extension of CSMA where nodes listen to the channel while transmitting to detect collisions. If a collision is detected, nodes stop transmission, wait for a random backoff time, and retry.
  • Application: CSMA/CD was used in traditional Ethernet networks, but it’s mostly obsolete now with the prevalence of full-duplex Ethernet.

3. CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance):

  • Concept: CSMA/CA is used in wireless networks where it’s difficult to detect collisions. Nodes wait for the channel to be idle and send a short “request-to-send” (RTS) signal. If no collision is detected, the receiver sends a “clear-to-send” (CTS) signal, and then data is transmitted.
  • Application: CSMA/CA is used in Wi-Fi networks (IEEE 802.11).

4. TDMA (Time Division Multiple Access):

  • Concept: TDMA divides the communication channel into time slots. Each user is allocated a specific time slot during which they can transmit data.
  • Application: TDMA is commonly used in cellular networks where each user gets a time slot for communication.

5. FDMA (Frequency Division Multiple Access):

  • Concept: FDMA divides the communication channel into frequency bands. Each user is allocated a separate frequency band for transmission.
  • Application: FDMA is used in analog communication systems like AM and FM radio.

6. Token Passing:

  • Concept: In token passing, a special token is passed around the network. Only the node holding the token is allowed to transmit data. After transmission, the token moves to the next node in the network.
  • Application: Token passing is used in Token Ring networks.

7. CDMA (Code Division Multiple Access):

  • Concept: CDMA assigns unique codes to each user. Users can transmit simultaneously over the same frequency band, and the receiver decodes the signals using the assigned codes.
  • Application: CDMA is used in cellular networks, such as CDMA2000 and WCDMA (UMTS).

These channel access techniques play crucial roles in regulating access to communication channels, managing bandwidth, and ensuring efficient data transmission in various types of networks. Each technique has its advantages and is suited to different network architectures and requirements.