Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA):
This is a wireless network multiple access method defined by IEEE 802.11 standard. CSMA/CA is a modification to CSMA/CD. Collision detection as in CSMA/CD is not applicable for several reason, one reason is Hidden Terminal Problem.
To understand this problem, considering that we have three stations 1, 2 and 3. Station 1 and 3 are sending packets to station 2 at the same time and it may that these two stations can’t hear each other and thus, collision will occur. To prevent this, collisions must be avoided as follows,
- The sending station after sensing the station idle sends a special small frame called Request to Send (RTS) in which the station defines the total time it needs the medium.
- The receiver after receiving the RTS sends a small packet Clear to Send (CTS) to all the stations meaning that it has received the RTS and the medium is clear.
- Then the sender sends the data frame.
- The receiver acknowledges the receipt of data.