How do WiFi chips know that a signal is an SSID?
How are SSID’s encoded to denote their signal type?
What does it take to generate an SSID?
Do I need a WiFi card to GENERATE an SSID or can the be generated and broadcasted separately?
SSID is an acronym meaning Service Set IDentifier, and is basically the (usually) human-readable name of a Wi-Fi network.
It is encoded in a few packets with ASCII characters, notably in almost every beacon and probe response packet (with a few exception, for example if the network is hidden).
So, being a name, generally it isn't "generated" but actually configured by someone, although in some cases it is automatically generated by an algorithm, for example in P2P applications such as a Wi-Fi printer with hotspot (or Wi-Fi Direct) capabilities. It is not a file, so it doesn't make sense for it to be generated and/or broadcasted.
I hope I catched your question, if not please clarify what you're looking for.
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wifi follows 802.11 standard to send/receive wifi signal.
Wifi Chip can knows AP's name (SSID) by AP's periodically broadcast signal called beacon.
If we sniffer wifi signal and decode it as above picture, there is an SSID IE which describes the name of AP. (e.g. openwrt-sae in this case)
Related
I am trying to send the wifi direct probe packets using raw sockets so that mobile devices will show them in wifi direct device list.
I am trying to capture packets first in Wireshark in monitor mode in order to understand the packet structure and compare with the P2P probe request packet mentioned in Wifi Direct specification.
But I am not able to capture the correct probe packet in Wireshark. Can anyone suggest me what I am missing in my approach?
I wasn't able to capture packets with filter WLAN.addr= XX:XX:XX:XX:XX:XX. (Actual wifi Mac address), as WiFi Direct Mac address is different and the first byte was different.For example If your wifi mac is 00:04:CB:CX:DE:E7 then WiFi-Direct address is 02:04:CB:CX:DE:E7.
Also, I am able to show the device listed when I sent probe response packet to the device.
If probe response packets announces the capabilities of a network,
then what is the purpose of Beacon frames in wireless 802.11 ?
Among other things, beacons allow a device to passively scan all channels for available Access Points so that a list may be presented to a user showing signal strength. They also allow a device to detect if there is another Access Point on the same network and presumably on a different channel with a better signal.
I'm creating an app that needs to connect to versions of itself running on other devices on the wifi network. The goal is to set up a broadcast / client relationship between one device to the others.
I know that Bonjour is the accepted method to do this, but I'm reticent to do that because it locks me into iOS devices, when I'd like to branch out to others, at least for clients.
If I start a webserver on the broadcaster on a specific port, like 43231 or something, is it acceptable for the client device to get it's own IP and then scan that block range for the broadcaster? Is there anything bad about pinging all the other random devices on the network with a request like that?
As in, Broadcaster is 192.168.1.11. Client is 192.168.1.4. If the client assumes all the devices are in the 192.168.1.* block, can it just iterate up the line from 1-100 or so looking for the broadcaster?
If this method is crazy, what should I do?
You can use SSDP (used by UPnP) or just multicast a message over the network and listen for it at the same time, ignoring the loopback (if you don't want the sender to receive it's own messages).
Maybe it will be better to use Bluetooth Low Energy for broadcasting/discovery? You can send non-connectable advertisement packets on server (with it's IP address) and listen for them on all other devices. Device founds such packet, reads IP address and connects to it via NSURLConnection (or something like that).
My understanding is that current WiFi driver uses rate control algorithm to choose a data rate within a small set of predetermined values to send packets over the WiFi medium. Different algorithms exist for this purpose. But how does this process work when WiFi driver decides that the connection is lost and shutdown the connection all together? Which part of the code should I read in open source WiFi driver such as MadWiFi and the likes?
The WiFi driver for your hardware which runs in Linux communicates with the WiFi chip which also runs a pretty complex firmware. The interface between the driver and the firmware is hardware specific. In some hardware the detection of connection loss events is done completely by the firmware and the driver only gets a "disconnected" event while in others the driver is also involved.
Regardless of who does what disconnection usually occurs due to either
Receiving a DEAUTH frame from the AP
Detecting too many missing beacons. Beacons are WiFi frames sent periodically by the AO (for most APs every ~100ms) . If you get too far from the AP or the AP was just powered off you stop seeing the beacons in the air and usually you'll signal disconnection or try to roam to a different AP.
Too many failures on Tx of packets (i.e. not receiving ACK frames for too much traffic)
This usually indicates that you've gone too far from the AP. It could be that you can "hear" the AP but it can't hear you already. In this case it also makes sense to signal a disconnection.
For example you can look in TI wifi driver in the Linux kernel drivers/net/wireless/ti/wlcore/events.c and the function wlcore_event_beacon_loss()
In Cfg80211 architecture, assume we are station mode.
driver call kernel API cfg80211_send_disassoc() if we received a deassoc/deauth frame.this function will notify corresponding application (ex wpa_supplicant) a disconnect event.
on another hand, when we decide to disconnect with AP, applicantion (ex wpa_supplicant) can call linux kernel API cfg80211_disconnected(), it will trigger corresponding driver ioctl function to finish disconnection task.
How do I transfer a file from one BlackBerry device to another over WiFi like I've done with blue tooth?
In Bluetooth, each device can easily become aware of one another because the protocol supports this. In Wifi (which is just a medium for generic networking... TCP/IP in many cases), it's generally expected that one machine already knows how to locate the other... so this is the problem you need to solve.
One option is that you can have one of the devices (or even both) periodically broadcast a message when it wants to connect to something; this message would be on a pre-defined port but as a broadcast, it's open to all receivers. Then the other device (or even both) needs to have a broadcast receiver looking for the message on the right port. One benefit here is the broadcast receiver will not only receive the message, it will also receive the IP address of the sender -- this is your missing component.
Once the receiver has the IP address of the sender, it needs to open a connection to the server port running on the device that sent out the broadcast. Of course, that first device needs to have its server task running at this time also.