I know I can send 802.11 custom packets with wifi_send_pkt_freedom, and I'am using it without any problem.
But what about receiving?. Yes, I can enable promiscuos mode, and filter by MAC address. Doing that is perfect for sniffing, but not for communication, because the ESP8266 won't ACK the packets and if I'am not sniffing and my ESP is the only receiver, it will make the transmitter to repeat many times the packet. Yes, I can send it like broadcast or multicast to avoid waiting for the ACK, but I'll missing the ACK/re-send functionality. In short I would like to put the ESP Wifi interface in monitor mode (which is not promiscuos mode)
And yes, I can use ESPNOW, but for my application it wont suit very well my needs.
Thanks!
Román
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I want to develop an android app which uses push to talk or Voip to communicate between 2 mobile devices using a Wi-Fi connection without using a data or the internet.
Is it possible to develop this?
I am looking for a 'free' Wi-Fi Walkie Talkie but I don't know how to start doing it?
For a very simple, initial version, I'd do the following:
Assign a static IP address on each phone
Record the audio and packetise it into a UDP stream that you'll send to the remote IP address
Repackage again the UDP stream and play the audio.
Microphone ---> Samples ----> UDP (over WiFi) ----> Samples ----> Speaker.
There are plenty of enhancements that you can add over the time:
Device discovery
Signalling separate (SIP or custom messages via TCP or UDP to indicate when to start the audio transmission and negotiate the media channel that will be used).
Support for third party devices (SIP)
Use standard paketization using RTP and encode the audio using G711alaw/G711ulaw...
There are plenty options, but you should start by capturing the audio, and sending it over the network, even make packets of 2 seconds with the incurring delay, but that's a point to start. Then, you should lower the packet length to contain 20ms of audio to avoid delays in the transmission.
Hope this helps.
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.
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.
Ideas:
1. Pinging all my subnet ( using simple ping etc )
2. Sending GET to all IP in my subnet? ( may be too slow) waiting for 200 or 404 reply.
Thanx
Can you program your ethernet device to respond to Bonjour (mDNS) requests? That's the preferred discovery mechanism in the OSX/iOS ecosystem. avahi is an open-source mDNS daemon you might be able to run if your device runs a UNIX-like OS. You might also be able to find or write an embeddable mDNS server that you could integrate into your server if you're not running an OS as such.
Otherwise, I'd probably go with a custom broadcast UDP packet that the device will respond to. (which is basically what Bonjour/mDNS does, but less general) To send a broadcast UDP packet, open a UDP (datagram) socket and send a packet to the local subnet's broadcast IP. Make the packet contents suitably unique, and get your device to respond, e.g. using an HMAC, to avoid picking up any other devices or daemons which coincidentally answer on the same port.
This is a pure IP networking question. What you want to do is to send a TCP/IP broadcast message to the network and have you custom device respond to it. See TCP/IP Guide for some basic details.