I understand that these days CSMA/CD i.e. ethernet one isn't used at all because we have full duplex network. Thus, there is no chance of collision here. Also, we don't use hubs anymore. Each switch port has a different collision domain. The question is in Wifi world - is CSMA/CA - collision avoidance is useful or not. I believe in 802.11 there is no concept of duplexity so how does it work?

  • 1
    @jonathanjo that's not a collision. The switch will buffer any frame that it cannot immediately transmit. (and drop any frame when there's no buffer space.) At no point will two (or more) frames overlap.
    – Ricky
    Commented Jun 21, 2018 at 19:24
  • @Ricky Beam, you're right of course, I was thinking of something else. I've deleted my error.
    – jonathanjo
    Commented Jun 21, 2018 at 20:26
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
    – Ron Maupin
    Commented Dec 25, 2018 at 8:54

2 Answers 2


CSMA/CA is used with Wifi and it's useful. Since "air" is generally a shared medium, no two stations must transmit simultaneously. Collisions are possible and need to be avoided/handled with.

"How does it work?" is much too broad to answer here.

With full-duplex links, no collision handling is required at all since there can be no collisions.

  • is there no concept of full / half duplexity in Wifi? If not then CSMA/CA will always come into the picture whereas CSMA/CD will not since these days we use full duplex all the time. Commented Jun 21, 2018 at 22:26
  • For wireless, full duplex would require two channels per link (or one channel for each transmitter) which isn't currently possible.
    – Zac67
    Commented Jun 22, 2018 at 5:03

CSMA/CD is used in Ethernet networks to prevent collisions by checking whether the medium is idle before sending a packet.

CSMA/CA is used in wireless networks to prevent collisions by checking whether the channel is idle before sending a packet.

Collisions can still occur in wireless networks, because two devices trying to access the access point at the same time causes a collision when both are authorised to use the same channel.

CSMA/CA is useful.

  • No. CD stands for collision detection and by the other hand CA stands for collision avoidance.
    – ESCM
    Commented Jul 8, 2021 at 4:41
  • Correct, but I don't see why you are saying no to my answer. Commented Nov 8, 2021 at 8:06

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