Sorry, I took a long break due to my busy schedule. As I said in the last post, now it is time to continue speaking about the beacons. Links of previous posts, yes they are just below.
Introduction to Wi-Fi
Wi-Fi Channels
Addresses in 802.11, Beacons
Frame format of Beacons
We will finish of the beacon discussion with this post. Beacons have lot and lot of things inside. I am skipping many things so that they can be covered when we speak about the specific topic. Whatever happens in the Wireless, Beacon definitely has a part in it. So all the things will get covered in one way or other. Well, have a look at the images below.
The beacons will also say us whether it is an IBSS (Independent BSS - without infrastructure device) or BSS (Infrastructure BSS). The other parameters such as block ack, apsd, Gmode short slot etc. we will see them in individual posts in near future.
Gentle intro to some of the terminologies used.
a. Block Ack - Sending a single acknowledgment for all the frames received.
b. Privacy - For using WEP the privacy bit will be 1, else it will 0.
c. Short preamble - This corresponds to the guard interval and the header symbols which are used for synchronization between receiver and transmitter. 10 such symbols are used in short preamble, where as 12 symbols are used in long preamble. After 802.11g we are using only the short preamble by default. Where as B only networks will use long preamble by default.
d. barker bit - To take care of the preamble differences, barker bits are used. Barker bits is set when a long preamble device operates on the same channel.
e. QoS - Quality of Service.
d. APSD - Automatic power save delivery. The QoS and APSD bits have separate headers defined by WMM.
In Next post we will speak about major differences between b and g, also about bg protection mechanisms.
Introduction to Wi-Fi
Wi-Fi Channels
Addresses in 802.11, Beacons
Frame format of Beacons
We will finish of the beacon discussion with this post. Beacons have lot and lot of things inside. I am skipping many things so that they can be covered when we speak about the specific topic. Whatever happens in the Wireless, Beacon definitely has a part in it. So all the things will get covered in one way or other. Well, have a look at the images below.
 | |
| Beacon Frame |
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| Beacon - Contd. |
The above two images shows the parameters for which the Infrastructure element is configured for. Like the SSID (Service Set ID - here abcd....vwx), Channel in which the network device is functioning (channel 5 here), Country (USI - United Nations I represents Indoor user), Channels supported (11 channels starting from 1) by the Infrastructure element.
In the second image, basic rates are the rates which are supported for a 802.11b only device. For 802.11g device there are certain extended support rates defined which is up to 54Mbps. There are some more headers called HT45 and HT61 which are meant for 11n standards and they are skipped. We will see them in detail on a series of separate posts. Similarly vendor specific information such as Security Scheme, WMM (Wi-Fi Multi-Media) they are also skipped and will be dealt as separate topics.
Gentle intro to some of the terminologies used.
a. Block Ack - Sending a single acknowledgment for all the frames received.
b. Privacy - For using WEP the privacy bit will be 1, else it will 0.
c. Short preamble - This corresponds to the guard interval and the header symbols which are used for synchronization between receiver and transmitter. 10 such symbols are used in short preamble, where as 12 symbols are used in long preamble. After 802.11g we are using only the short preamble by default. Where as B only networks will use long preamble by default.
d. barker bit - To take care of the preamble differences, barker bits are used. Barker bits is set when a long preamble device operates on the same channel.
e. QoS - Quality of Service.
d. APSD - Automatic power save delivery. The QoS and APSD bits have separate headers defined by WMM.
In Next post we will speak about major differences between b and g, also about bg protection mechanisms.
