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What Prevents All the Wi-Fi Devices on my Network from Colliding with Each Other?

Your home network is likely packed with various Wi-Fi devices transmitting back to the Wi-Fi node; how does the the node handle all the traffic without all the incoming transmissions colliding?

Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.

The Question

Superuser reader Zequez is curious how his Wi-Fi node seems to function so smoothly and why the data does appear to collide, he writes:

I mean, I know each packet is sent with a MAC address, but what about streaming?

What happen if while the router is receiving one packet, a packet from another device arrives?

How can the router knows that the photons colliding into the antenna are part of the first packet or the second packet?

Or is it that the speed of light is so fast that this almost never happen and the packets are just reported as corrupt and are sent again?

What keeps all those wirelessly delivered packets in order? Let’s dig a little deeper.

The Answer

SuperUser contributor Ultrasawblade offers the following answer with helpful links for further reading:

In a wireless network, only one device is actually “speaking” at once. Each other device listens and waits for the air on that channel to be quiet before speaking. This technique is called carrier sense multiple access with collision avoidance (CSMA/CA).

An RTS/CTS exchange helps all the nodes stay in sync efficiently by providing a way for one node to say “hey, I’m going to talk for this long so wait this long” to every other node.

@Petr Abdulin is correct but I think all Wifi networks use CSMA/CA. Old 10BaseT non-switched wired networks relied on carrier sense multiple access with collision detection (CSMA/CD). Collisions don’t happen on networks where all nodes are connected to a switch.


Have something to add to the explanation? Sound off in the the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.

Jason Fitzpatrick is warranty-voiding DIYer and all around geek. When he's not documenting mods and hacks he's doing his best to make sure a generation of college students graduate knowing they should put their pants on one leg at a time and go on to greatness, just like Bruce Dickinson. You can follow him on if you'd like.

  • Published 03/5/13

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