Greg Hammond

I briefly went over the frames used to connect a STA to a BSS in this post but I also wanted to show more details on what each of them contain. Since the Probe Request is the first frame to explicitly start the joining process we will start here. You can also look at other info about Probe Requests and other frames from my CWAP Notes section. These are sent by the STA wishing to join a certain BSS and will request additional info about the network. However, the info contained in the request is that of the STA sending it. We will find a lot of information about what the client is capable of in this frame. Ive included a visual representation of the mac header and frame control field to make it easier to see how this all works together.  .11 MAC Header Frame Control field Beginning with the info in the Frame Control field, here is a Probe Request I captured on my own network.  We see some information that will be useful when doing packet captures with a protocol analyzer. I...

 RTS / CTS, What is it? When learning about the .11 protocol you will probably come across these terms, RTS or Request to Send and CTS or Clear to Send. Both of these frames are used in conjunction with each other to further control the medium. While we still have CSMA/CA and EDCA to moderate and prioritize various transmissions over the medium, in areas of high utilization or when large frames are used we need additional help. RTS/CTS helps us 'reserve' the medium for a period of time.    Initially a STA will send a RTS frame to an AP and include the duration it needs for transmission including the SIFS and PHY duration needed for the AP to respond. When the AP sends the CTS frame, its duration field will be the duration found in the RTS minus the CTS and minus the SIFS interval for that PHY.  Ive added some packet captures I did on my home network below so we can see the duration fields of each frame type and further understand how it is calculated.  We can cl...