Answer:

CSMA:

CSMA stands for Carrier Sense Multiple Access. It is a Media Access Control protocol that is used to control the flow of data in a transmission media so that packets do not get lost and data purity is preserved. There are two modifications to CSMA that are the CSMA CD (Collision Detection) and CSMA CA (Collision Avoidance) where each modification having its own strengths.

The difference between CSMA/CD and CSMA/CA are shown below:

1. CSMA/CD takes effect after a collision while CSMA CA takes effect before a collision.
2. CSMA CD only minimizes the recovery time while CSMA/CA trims the possibility of a collision.
3. CSMA/CD is commonly used in wired networks while CSMA/CA is used in wireless networks.

CSMA-CD not used in WLAN because of two main reasons that shown below:

• Implementing a collision detection procedure would need the implementation of a full duplex radio capable of transmitting and receiving at the same time, an approach that would increase the cost powerfully.
• In a wireless environment we cannot assume that all stations hear each other and the fact that a station wants to transmit and senses the medium where the medium is free around the receiver area.

To overcome these difficulties, CSMA-CA mechanism can be used in the place of collision detection (CSMA-CD) mechanism. CSMA-CA is used on wireless networks. CSMA-CA doesn’t detect collisions but quite avoids them through the use of a control message. The control message collides with another control message from another node, it means that the medium is not available for transmission and the back-off algorithm needs to be applied before attempting retransmission.

Answer:-
Difference between CSMA/CD & CSMA/CA are as follows

1. CSMA / CD is effective after a collision. Whereas CSMA / CA is effective before a collision.
   1. CSMA / CD is used in wired network. Whereas CSMA / CA is commonly used in wireless networks.
   2. CSMA / CD only reduces the recovery time. Whereas CSMA/ CA minimizes the possibility of collision.
   3. CSMA / CD resends the data frame whenever a conflict occurs.Whereas CSMA / CA will first transmit the intent to send for data transmission.
   4. CSMA / CD is used in 802.3 standard. Whereas CSMA / CA is used in 802.11 standard.
   5. CSMA / CD is more efficient than simple CSMA(Carrier Sense Multiple Access). Whereas CSMA / CA is similar to simple CSMA(Carrier Sense Multiple Access).

CSMA/CD cannot be implemented in Wireless LAN because of following reasons:-

In CSMA/CD, if a collision is detected on the medium, end-devices would have to wait a random amount of time before they can start the retransmission process. But in wireless LAN, there is no way for the sender to detect collisions the same way CSMA/CD does in wired networks since the sender is only able to transmit and receive packets on the medium but is not able to sense data traversing that medium. Thus CSMA/CD cannot be implemented in Wireless LAN.

But CSMA/CA can be used in wireless LAN because CSMA/CA doesn't detect collisions but rather avoids them through the use of control message. The control message collide with another control message from another node, it means that the medium is not available for transmission and the back-off algorithm needs to be applied before attempting retransmission.