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Consider the following scenario:

  • AP is an access point with internet connectivity and in idle state (ie: no node is connected to it)
  • N is a node that wants to establish an internet connection through AP

1st Issue
What is the minimum amount of packets that they must exchange in order for N establish an internet connection? (ie: be able to use standard browsers and sockets api)

2nd Issue
What are the names of those packets? Briefly, what those packets do?

Motivation
Recently I've installed WinPcap to see what packets were being exchanged between my router and my computer. As soon as you connect to the router (ie: the user is not transferring any data), several hundreds of packets are transmitted. Here goes a small list of the first packets and their correspondent time + length:

listening on Network adapter 'Microsoft' on local host...
14:27:46,534048 len:42
14:27:46,537764 len:346
14:27:46,541692 len:42
14:27:46,541694 len:590
14:27:46,541721 len:74
14:27:46,554746 len:149
14:27:46,555292 len:74
14:27:46,568235 len:90
14:27:46,568765 len:90
14:27:46,571916 len:42
14:27:46,586545 len:42
14:27:46,588601 len:90
14:27:46,589166 len:46
14:27:46,597994 len:87
14:27:46,598158 len:67
14:27:46,603153 len:62
14:27:46,695175 len:87
14:27:46,695301 len:67
14:27:46,833377 len:42
14:27:46,835398 len:42
14:27:46,837512 len:86
14:27:46,837756 len:66
14:27:46,892574 len:85
14:27:46,944622 len:86
14:27:46,944774 len:66
14:27:46,991309 len:42

After some seconds, even without the user transferring any data, this list continues to grow even larger (some thousands of packets).

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2 Answers 2

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Wi-Fi has a several types of frames used for management:

  • Association request frames
  • Association response frames
  • Authentication frames
  • Beacon frames
  • Deauthentication frames
  • Disassociation frames
  • Probe request frames
  • Probe response frames
  • Reassociation request frames
  • Reassociation response frames

Wi-Fi also has a few types of frames used for control:

  • Request to Send (RTS) frames
  • Clear to Send (CTS) frames
  • Acknowledgement (ACK) frames

Of course, the point of Wi-Fi is to transmit data, so there are also

  • Data Frames.

A discussion of all these frames and how they are used can take several chapters in books, so it it too broad to discuss here. You should search for "Wi-Fi frame types" using Google to find full explanations of how it all works.

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  • too broad to discuss here Sure, but your answer is already just fine for me.
    – Mark Messa
    Commented Jan 3, 2016 at 17:28
  • A discussion of all these frames [...] take several chapters in books Besides google search and IEEE standards for 802.11, would you recommend any other source?
    – Mark Messa
    Commented Jan 3, 2016 at 17:33
  • That's really quite a lot material. Unfortunately, I don't know any specific books off the top of my head, and resource recommendations are off-topic.
    – Ron Maupin ♦
    Commented Jan 3, 2016 at 17:36
  • Wi-Fi has a several types of frames used for management: I'm not sure, but I guess that WinPcap doesn't capture several of those management & control frames. Do you agree? Because, if so, what are all those packets being captured?
    – Mark Messa
    Commented Jan 3, 2016 at 17:38
  • You may want to use something like Wireshark which has more knowledge of the different frame types. It uses WinPcap, but it knows more about what you are seeing.
    – Ron Maupin ♦
    Commented Jan 3, 2016 at 17:46
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On a Windows PC, odds are you are not capturing the Wi-Fi control frames -- most Wi-Fi drivers don't let you switch to "monitor mode."

The average number of control frames you need is three to five.

Under that assumption, the large number of packets you are seeing are seeing various process on your PC making connections to various servers. A lot depends on the software you have on your PC. Depending on the version, Windows might check for a valid license, software update, etc. It also probes MS servers to see if in fact you do have Internet connectivity. Your antivirus might also do check for updates. Email and cloud services like Dropbox can also start connections when there is Internet connectivity.

A full discussion of those applications would be better suited for Superuser, as operating systems and applications are off-topic here.

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  • most Wi-Fi drivers don't let you switch to "monitor mode." Ok, I agree. The source code explicitly states 'promiscuous mode' instead of 'monitor mode'. Even so, as far as I know, Windows emulates a 'fake ethernet'. Therefore, control/management frames doesn't pass to the application since there is no equivalent to them in Ethernet.
    – Mark Messa
    Commented Jan 3, 2016 at 18:28
  • The average number of control frames you need is three to five. Ok, this is an important information. To establish a L2 connection all you need is roughly 5 frames.
    – Mark Messa
    Commented Jan 3, 2016 at 18:29
  • To be more specific, that's what you need to associate with the AP.
    – Ron Trunk
    Commented Jan 3, 2016 at 18:30
  • A full discussion of those applications would be better suited for Superuser Ok, the other issue I would like to solve is how many packets you must exchange in order for the OS recognize an internet connection and let you browse properly. But this one I will follow your advice and post at Superuser. Thanks!
    – Mark Messa
    Commented Jan 3, 2016 at 18:33
  • If you do as @Ronmaupin says and install Wireshark, you can see the destination addresses of the IP packets. That will give you a pretty good clue as to whom your PC is talking to.
    – Ron Trunk
    Commented Jan 3, 2016 at 18:36

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