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It's not widely used today the way broadcast TV was, but there is multicast. Twenty years ago, I was watching NASA TV streamed over the Mbone.
There, the routers are set up to handle sending packets to multiple specific destinations, one-to-many, so it is pretty efficient.
I've wondered for a long time if it is possible to use WiFi as broadcast/multicast? I mean, i understand that it won't work out of the box, but if one was to write code from ground up (ie different TCP protocol) can it be made possible to, say, transmit video lecture from one WiFi router and for multiple mobile phones to receive and view it without individually being connected to the network. Kind of like how everyone is able to view the SSID of the WiFi node without being connected.
Or is it a hardware level problem that I can't wrap my head around. I have wanted to understand this for a long time but I don't have a background in this subject and don't know the right questions to ask. Even the LLM based search tools have not been of much help.
You can broadcast to everyone connected to a WiFi network. That's just an Ethernet network, and there's a broadcast address on Ethernet.
Typically, WiFi routers aren't set up to route broadcasts elsewhere, but with the right software, like OpenWRT, a very small Linux distribution, you can bridge them to other Ethernet networks if you want.
Internet Protocol also has its own broadcast address, and in theory you can try to send a packet to everyone on the Internet (
255.255.255.255), but nobody will have their IP routers set up to forward that packet very far, because there's no good reason for it and someone would go and try to abuse it to flood the network. But if everyone wanted to, they could.I don't know if it's what you're thinking of, but there are some projects to link together multiple WiFi access points over wireless, called a wireless mesh network. It's generally not as preferable as linking the access points with cable, but as long as all the nodes can see each other, any device on the network can talk to others, no physical wires. I would assume that on those, Ethernet broadcasts and IP broadcast packets are probably set up to be forwarded to all devices. So in theory, sure.
The real issue with broadcast on the Internet isn't that it's impossible to do. It's just that unlike with TV, there's no reason to send a packet to everyone over a wide area. Nobody cares about that traffic, and it floods devices that don't care about it. So normally, the most you'll see is some kind of multicast, where devices ask that they receive packets from a given sender, subscribe to them, and then the network hardware handles the one-to-many transmission in a sort of star architecture.
You can also do multicast at the IP level today, just as long as the devices are set up for it.
If there were very great demand for that today, say, something like Twitch TV or another live-streaming system being 70% of Internet traffic the way BitTorrent was at one point, I expect that network operators would look into multicast options again. But as it is, I think that the real problem is that the gains just aren't worth bothering with versus unicast.
kagis
Today, looks like video is something like that much of Internet traffic, but it's stuff like Netflix and YouTube, which is pretty much all video on demand, not a live stream of video. People aren't watching the network at the same time. So no call for broadcast or multicast there.
If you could find something that a very high proportion of devices wanted at about the same time, like an operating system update if a high proportion of devices used the same OS, you could maybe multicast that, maybe with some redundant information using forward error correction so that devices that miss a packet or two can still get the update, and ones that still need more data using unicast to get the remaining data. But as it stands, just not enough data being pushed in that form to be incredibly interesting bothering with.
I'm honoured that you took the time to type all this out but it looks like I've failed yet again at conveying what I meant to ask and I'll try to rephrase:
What you have been explaining is broadcasting when all devices are connected to the same network. I want to understand if it is possible to use WiFi just like a radio to broadcast data, without actually connecting. A device can transmit/broadcast, say, a video over the EM waves using some kind of modulation like they do in FM. The receiving devices, like our phones, already have hardware to receive these waves and process it to extract the information. Like I said, it already happens where the SSID of the WiFi transmitter/router is seen by all devices without actually connecting.
And before you say anything, yes I'm aware that it is a very small amount of data being 'transmitted' at a very low bitrate. But what is the limiting factor? Why can't much more data be transmitted this way?
I'm really sorry if there is a silly answer to this as I'm sure there must be. But, like I said, i could never find it in my searches.
Thanks and cheers!
Yes, at least some WiFi adapters can. Software used to attack WiFi connections, like
aircrack, does this by listening and logging (encrypted) packets without authenticating to the access point, and then attempting to determine an encryption key. You can just send unencrypted traffic the way you do today, and software could theoretically receive it.However, this probably won't provide any great benefit. That is, as far as I know, just being connected to a WiFi access point shouldn't generate much traffic, so you could have a very large number of computers authenticated to the WiFi access point -- just set it not to use a password -- without any real drawback relative to having the same machines snooping on unencrypted traffic.
WiFi adapters cannot listen to multiple frequencies concurrently (well, unless things have changed recently), so it won't let you easily receive data from more access points simultaneously, if you're thinking of having them all send data simultaneously.
The typical home routers don't support more than 20-25 simultaneous connections last i checked. I'm sure there must be professional devices that allow thousands of connections like they use in public wifi spots but I'm also sure they would be much pricier.
At this point, it is just a pursuit for understanding how these things work and if what I want can actually be made possible as alternative use case of WiFi, especially given how ubiquitous it is.
Thank you for indulging me nonetheless.
You can do UDP multicast with WiFi today just fine. No one does, though.