Beacon vs Probe Response frame
| No | Beacon | Probe Response |
| Differences | ||
| 1. | It is always Broadcast. | It is always unicast. |
| 2. | Its Duration field is 0 because of point 1. | It has some value in duration field because of point 1. |
| 3. | It has TIM field which includes DTIM. | It does not have TIM field. |
| Similarities | ||
| 1. | Both frame types are management frame. | |
| 2. | Both have timestamp and Beacon interval field. | |
| 3. | Both have same capabilities information field. | |
| 4. | Both have same SSID field, Supported rate and WMM field. | |
| 5. | Both have ERP filed but Wi-Fi STA follows the ERP from Beacon frame for this. | |
| 6. | Both have HT information subset for HT protection but Wi-Fi STA follows the ERP from Beacon frame for this. |
If you have more important points for this post. Please let me know in comment section.
Sandy
Hi Bamdeb ,
Thanks for your post .
How a mobile or laptop generates a scan list of AP’s SSIDs ? Here my doubt is when we open the Wi-Fi interface we can see list of SSIDs , is it done by which type of scanning (active or passive) . Simply listening to the beacons will generate the scan list or need to send probe requests and collecting the probe responses will generate the SSIDs list in the devices . Can you please help me on this ?
Bamdeb
Thank you for reading the post.
I hope you already read this post also.
https://wifisharks.com/category/wifi/wlan-basic/scanning/
Now coming to your questions:
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—–>As there are two types of scanning available then it depends on the device type and implementation.
Example: As mobile device is mainly battery operated then mobile device tries to do passive scanning mainly. But it can do active scanning before connection.
On the other hand , laptop can be mainly external powered, so it does active scanning but again when it’s on battery then passive scan be chosen.
So it’s all implementation dependent based on situations. We cannot know this by seeing the scan list. Both scanning mechanism is used.
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—> Both can generate scan list.
Anamika Raj
why is beacon required when probe response is already there? Can beacon frame be replaced with probe response?
Bamdeb
Hi Anamika Raj,
Thanks for reading the post.
Here are the some reason why do you need Beacon frame
1-> Beacon frame is an Broadcast frame and it’s like AP is advertising its own capabilities.
So it is easy to see AP’s capabilities by STA by doing only Passive Scan. STA does not have to send any frame to get AP’s information. Battery is saved for STA. Example: Your Android Phone WiFi scan uses Passive scan sometimes.
You can see active and passive scan in details in another post.
2-> Check point number 3 from post. Beacon frame carries buffered data information for connected STA in TIM or multicast data in DTIM. This is not possible in probe response frames it is unicast.
3-> All connected STA get time synced with Beacon as it comes as broadcast.
4-> Powersave STA can wake up in listen interval or any other time to check beacon if there is any buffer data. With probe response it’s possible.
5-> Again , as Beacon is broadcast frame , you can see Ap’s details in sniffer easily without depending on any probe response. Because to get probe response at least one STA has to send probe request.
These are the common reason i got , You can think many other reason easily.
Thanks
Bamdeb