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Difference between CSMA/CA and CSMA/CD
Both CSMA/CA and CSMA/CD are network protocols for transmission that operate in the Medium Access Control Layer, however there are significant differences in the way they operate. Read through this article to find out more about CSMA/CA and CSMA/CD and how they are different from each other.
What is CSMA/CA?
CSMA/CA is a network protocol for carrier transmission that stands for Carrier Sense Multiple Access with Collision Avoidance. It works in the same media access control layer as CSMA/CD. This protocol is effective before the collision.
Algorithm of CSMA/CA
The algorithm of CSMA/CA is as follows −
When a frame is ready, the transmitting station checks whether the channel is idle or busy.
If the channel is not clear, the node starts to wait for a random amount of time before checking to see if it is clear. This waiting period of time is known as the "back off factor" which is counted down by a back off counter.
If the channel is idle, the station waits for an Inter-frame gap (IFG) amount of time and then sends the frame.
It sets a timer after sending the frame.
The station then waits for acknowledgement from the receiver. If it receives the acknowledgement before expiry of timer, it marks a successful transmission.
Otherwise, it waits for a back-off time period and restarts the algorithm.
CMSA/CA prevents collision. As it waits for acknowledgements, data is not lost unnecessarily and it avoids wasteful transmission. CSMA/CA is very much suited for wireless transmissions.
What is CSMA/CD?
CSMA/CD stands for Carrier Sense Multiple Access / Collision Detection. It is also a network protocol for transmission and operates in the Medium Access Control Layer.
It detects when the shared channel for broadcasting is busy and stops the broadcast till the channel becomes available. Collisions in CSMA/CD are identified via broadcast sensing from other stations.
In CSMA/CD, when a collision is recognized, the transmission is halted, and the stations send a "jam signal", after which the station waits for a random time context before retransmission.
After sending a frame, a station monitors the medium to determine if the transmission was successful. If the station is successful, it is completed; if not, the structure is sent again.
Algorithm of CSMA/CD
The CSMA/CD algorithm is as follows −
The transmitting station examines if the channel is idle or busy when a frame is ready.
If the channel is congested, the station will wait till it becomes available.
If the channel is empty, the station begins transmitting and watches the channel for collisions
The station initiates the collision resolution procedure if a collision is detected.
The station resets the retransmission counters and completes frame transmission.
Although CSMA/CS detects collisions, it does not have a mechanism to reduce the number of collisions. Hence, it is not appropriate for large networks, as the performance degrades exponentially when more stations are added.
Difference between CSMA/CA and CSMA/CD?
The following table highlights the major differences between CSMA/CA and CSMA/CD.
|Effectiveness||CSMA/CA is effective before a collision.||CSMA/CD is effective after a collision.|
|Network Type||CSMA/CA is generally used in wireless networks.||CSMA/CD is generally used in wired networks.|
|Recovery Time||CSMA/CA minimizes the risk of collision.||CSMA/CD reduces the recovery time.|
|CSMA/CA initially transmits the intent to send the data. Once an acknowledgment is received, the sender sends the data.||CSMA/CD resends the data frame in case a conflict occurs during transmission.|
|CSMA/CA is part of the IEEE 802.11 standard.||CSMA/CD is part of the IEEE 802.3 standard.|
|CSMA/CA is similar in efficiency as CSMA.||CSMA/CD is more efficient than CSMA.|
From the above discussion, we can conclude that both CSMA/CA and CSMA/CD are network protocols for carrier transmission, however CSMA/CA is effective before a collision, whereas CSMA/CD is effective after a collision. CSMA/CD deals with collisions after their occurrence, whereas CSMA/CA prevents collisions prior to their occurrence.
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