802 Protocol frame format

802.11 and Wi-Fi Technology is not the same thing .Wi-Fi The standard is 802.11 A subset of the standard , And is Wi-Fi The alliance manages

802 Protocol frame format :

agreement Year of issue / date Op. Standard bandwidth The actual speed ( standard ) The actual speed ( Maximum ) Radius range ( indoor ) Radius range ( Outside )
Legacy 1997 2.4-2.5 GHz 1 Mbit/s 2 Mbit/s  ?  ?
802.11a 1999 5.15-5.35/5.47-5.725/5.725-5.875 GHz 25 Mbit/s 54 Mbit/s about 30 rice about 45 rice [3]
802.11b 1999 2.4-2.5 GHz 6.5 Mbit/s 11 Mbit/s about 30 rice about 100 rice
802.11g 2003 2.4-2.5 GHz 25 Mbit/s 54 Mbit/s about 30 rice about 100 rice
802.11n 2009 2.4 GHz or 5 GHz bands 300 Mbit/s (20MHz*4 MIMO) 600 Mbit/s (40MHz*4 MIMO) about 70 rice about 250 rice
802.11p 2009 5.86-5.925 GHz 3 Mbit/s 27 Mbit/s about 300 rice about 1000 rice
802.11ac 2011.11 5 GHz 433Mbit/s, 867Mbit/s (80MHz), (160MHz Optional ) 867Mbit/s, 1.73 Gbit/s, 3.47 Gbit/s, 6.93 Gbit/s (8 MIMO, 160MHz) about 35 rice [4]

Classification of wireless network protocol frames

Types and fields define three types of wireless networks , Namely :

1: Management frames, Its main function is to maintain the communication between the access point and the wireless client , The management framework has the following subtypes :

Authentication

De-authentication

Association Request

Association Response

Reassociation Request

Reassociation Response

Disassociation

Beacon

Probe Request

Probe Response

2:  Control frames

Control frame is responsible for data exchange between client and access point , The type is :

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

This data can be seen in some message requests .

3: Data frames

These different types of packets are collectively referred to as " Packet type ".

WLAN There are three network topologies

1) Independent basic service set (Independent BSS, IBSS) The Internet ( Also called ad-hoc The Internet )
2) Basic services set (Basic Service Set, BSS) The Internet
3) Extended service set (Extent Service Set, ESS) The Internet

1) AD-Hoc The Internet

win7 Self contained AD-Hoc Build function , It's very convenient for us to quickly build in a small range " LAN ", It's very convenient to play online games

2) BSS The Internet

For individuals PC Come on , The most used so-called " wireless Wi-Fi" Refers to BSS Network mode , We go through AP(Access Point) Access point to access the network

3) ESS The Internet

among ,ESS Medium DS( Distributed systems ) It's an abstract system , Used to connect different BSS The communication channel of ( Through routing services ), In this way... Can be eliminated BSS in STA And STA The direct transmission distance between them is limited by physical devices .

There are three types of wireless network protocol frames

We know that the data link layer is a communication protocol very close to the bottom layer , It USES Bit To represent information ( Also used Bit To identify the beginning and end of a packet ), So the protocol format of data link layer does not require a fixed length , namely 802.11 The length of the protocol is variable . The data frame length of different functions will be different . This characteristic shows that mac802.11 Data frames are more flexible , However , It's going to be more complicated .

mac 802.11 The length of the data frame varies mainly due to the following

. mac The number of addresses varies , Depending on the frame type ,mac .11 Of mac The number of addresses will be different . for instance ACK There's only one frame mac Address , And data frames have 3 individual mac Address , stay WDS In mode , The frame header has 4 individual mac Address .
. .11 The length of the information carried by the management frame varies , In the management frame , It's not just something like mac Address , Information like slice marks , And there will also be some other information , This information is about security settings , It's about physics
communication , For example, our SSID The name is obtained by managing frames .AP Management frames containing different information will be sent according to different situations .
. encryption (wep,wpa etc. ) Information ,QOS(quality of service) Information , If the data frame format with encryption is different from that without encryption , The encrypted data frame format also has an encryption header , For decryption . Then QOS The same is true

1:  Control frame

0x0: Frame Control Byte structure :

2: Manage frames

0x1: Manage frame protocol formats

(Beacon( beacon ) frame )

(Probe Request( Detection request ) frame )

(Probe Response( Detection response ) frame )

(ATIM frame )

(Disassociation( Disassociate ) And Deauthentication( De Certification ) frame )

(Association Request( Association request ) frame )

(Reassociation Request( Re association request ) frame )

(Authentication( Identity Authentication ) frame )

Manage frame protocol formats Byte order parsing :

. Frame control structure (Frame Control)
) Protocol Version: ( Protocol version ) Usually it is 0
) Type: The frame type , Manage frames :
) Subtype: Further determine the sub type of the frame
3.1) Beacon( beacon ) frame
3.2) Probe Request( Detection request ) frame
3.3) Probe Response( Detection response ) frame
3.4) ATIM frame
3.5) Disassociation( Disassociate )
3.6) Deauthentication( De Certification ) frame
3.7) Association Request( Association request ) frame
3.8) Reassociation Request( Re association request ) frame
3.9) Authentication( Identity Authentication ) frame
) To DS: Indicates whether the frame is BSS towards DS Frames sent
) From DS: Indicates whether the frame is DS towards BSS Frames sent
) More Fragment: It is used to describe the case that a long frame is segmented , Is there any other frame , If so, the value is set to 1
) Retry( Retransmission domain ): Indicates that the segment is a retransmission frame of the previous transmission segment .
) Power Management: After the frame is transmitted , Power management mode adopted by the station
8.1) by 1: STA be in power_save Pattern
8.2) by 0: STA be in active Pattern
) More Data: It means that many frames are cached in the station . That is, there is at least one data frame to send to STA Is set to 1.
) Protected Frame: Express basis WEP(Wired Equivalent Privacy) The algorithm encrypts the main frame . If the body part of the frame contains the data processed by the key set , Is set to 1, Otherwise set to 0
) Order( Serial number field ): In long frame segment transmission , The domain is set to 1 Indicates that the receiver should process the frame in strict order , Otherwise set to 0
. Duration/ID( The duration of the / identification )
Indicates how long the frame and its acknowledgement frame will occupy the channel ,Duration The value is used for the network assignment vector (NAV) Calculation
. Address Fields( Address field ):
) Destination Address
) Source Address
) BSS ID
. Sequence Control( Sequence control domain ): Used to filter duplicate frames
) MSDU(MAC Server Data Unit), 12 A serial number (Sequence Number)
) MMSDU(MAC Management Server Data Unit), 4 Bit segment number (Fragment Number) form
. Frame Body(Data): Information sent or received . For different types of data frames , The format of this field is quite different
) Beacon( beacon ) frame
1.1) Timestamp( timestamp ) position : Can be used to synchronize BSS Workstation in BSS The main timer of will send the microseconds that have been used at present . When the counter reaches the maximum value , We'll start counting from the beginning
1.2) Beacon interval position : AP Points are sent out at regular intervals Beacon( beacon ) The signal , To announce .11 The existence of the Internet . We can see a lot when we turn on the wireless connection Wi-Fi The point is because of it
1.3) Capability information position : send out Beacon When it's a signal , It's used to inform the parties , What kind of performance does the network have
1.4) SSID Service set identity (Service Set Identity): A string of bytes , Used to identify the network to which you belong BSSID, That is, we are in Wi-Fi The name of the access point you see before connecting
1.5) Frequency hopping parameter combination (PH Parameter Set): It includes joining .11 frequency hopping (frequency-hopping) The parameters needed by the network
1.6) Direct sequence parameter set (DS Parameter Set): Indicates the number of channels used by the network
1.7) Competition free parameter set (CF Parameter Set): Appears in support of contention free access points sent by Beacon In the frame , It's not necessary to
1.8) IBSS Parameter set (IBSS Parameter Set): To specify ATIM window ( The data to be transmitted indicates that the information interval is )
1.9) TIM Data to be transmitted information (Traffic Indication Map): Indicates which workstations need to receive the data to be transmitted
1.10) Country: National identification code
1.11) Power limit (Power Constraint): Allow the network to communicate its maximum transmission power to the workstation
1.12) Channel switching announcement (Channel Switch Announcement): To warn the workstations in the network that they are about to change channels
1.13) Silence (Quiet): To avoid interfering with specific military radar technology
1.14) Transmit power control report (TPC Report): Indicates the attenuation of the link , It can help the workstation understand how to adjust the transmission power
1.15) Extend the physical layer (ERP)
1.16) Support rate (Supported Rates): WLAN supports several standard rates . When the mobile station tries to join the network , The data rate used by the network will be checked first . Some rates are mandatory , Every workstation must support
, Some are selective
1.17) RSN Strong security network (Robust Security Network)
) Probe Request( Detection request ) frame
2.1) SSID Service set identity (Service Set Identity): A string of bytes , Used to identify the network to which you belong BSSID, That is, we are in Wi-Fi The name of the access point you see before connecting
2.2) Supported Rate( Support rate )
2.3) Extended support rate (Extended Supported Rate)
) Probe Response( Detection response ) frame
3.1) Timestamp( timestamp ) position : Can be used to synchronize BSS Workstation in BSS The main timer of will send the microseconds that have been used at present . When the counter reaches the maximum value , We'll start counting from the beginning
3.2) Beacon interval position : AP Points are sent out at regular intervals Beacon( beacon ) The signal , To announce .11 The existence of the Internet . We can see a lot when we turn on the wireless connection Wi-Fi The point is because of it
3.3) Capability information position : send out Beacon When it's a signal , It's used to inform the parties , What kind of performance does the network have
3.4) SSID Service set identity (Service Set Identity): A string of bytes , Used to identify the network to which you belong BSSID, That is, we are in Wi-Fi The name of the access point you see before connecting
3.5) Support rate (Supported Rates): WLAN supports several standard rates . When the mobile station tries to join the network , The data rate used by the network will be checked first
3.6) Frequency hopping parameter combination (PH Parameter Set): It includes joining .11 frequency hopping (frequency-hopping) The parameters needed by the network
3.7) Direct sequence parameter set (DS Parameter Set): Indicates the number of channels used by the network
3.8) Competition free parameter set (CF Parameter Set): Appears in support of contention free access points sent by Beacon In the frame , It's not necessary to
3.9) IBSS Parameter set (IBSS Parameter Set): To specify ATIM window ( The data to be transmitted indicates that the information interval is )
3.10) Country: National identification code
3.11) FH Hopping Parameters
3.12) FH Pattern Table
3.13) Power limit (Power Constraint): Allow the network to communicate its maximum transmission power to the workstation
3.13) Channel switching announcement (Channel Switch Announcement): To warn the workstations in the network that they are about to change channels
3.14) Silence (Quiet): To avoid interfering with specific military radar technology
3.15) IBSS Dynamic options (IBSS DFS): stay IBSS The workstation in charge of dynamic frequency selection can transmit in the management frame IBSS DFS Information elements
3.16) Transmit power control report (TPC Report): Indicates the attenuation of the link , It can help the workstation understand how to adjust the transmission power
3.17) Extend the physical layer (ERP)
3.18) Extended support rate (Extended Supported Rate)
3.19) RSN Strong security network (Robust Security Network)
) ATIM frame
) Disassociation( Disassociate )
5.1) Beacon Code
) Deauthentication( De Certification ) frame
6.1) Beacon Code
) Association Request( Association request ) frame
7.1) Capability information position : send out Beacon When it's a signal , It's used to inform the parties , What kind of performance does the network have
7.2) Listen interval position : To save battery power , The workstation can be temporarily shut down .11 The antenna of the network interface . When the workstation is dormant , The access point has to hold frames for it
7.3) SSID Service set identity (Service Set Identity): A string of bytes , Used to identify the network to which you belong BSSID, That is, we are in Wi-Fi The name of the access point you see before connecting
7.4) Supported Rate( Support rate )
) Reassociation Request( Re association request ) frame
8.1) Capability information position : send out Beacon When it's a signal , It's used to inform the parties , What kind of performance does the network have
8.2) Listen interval position : To save battery power , The workstation can be temporarily shut down .11 The antenna of the network interface . When the workstation is dormant , The access point has to hold frames for it
8.3) Current AP Address position : Use Current AP Address( The address of the current access point ) Bit to indicate the... Of the currently connected access point MAC Address
8.4) SSID Service set identity (Service Set Identity): A string of bytes , Used to identify the network to which you belong BSSID, That is, we are in Wi-Fi The name of the access point you see before connecting
8.5) Supported Rate( Support rate )
) Authentication( Identity Authentication ) frame
9.1) Authentication Algorithm Number: Indicates the type of authentication used by the authentication program
9.2) Authentication Transaction Sequence Number: To track the progress of Authentication
9.3) Status Code: Status codes are used to indicate the success or failure of a process
9.4) Question the password (Challenge Text): .11 A shared key authentication system is defined . The mobile workstation will be required to successfully decode an encrypted challenge password . This challenge password is sent through Challenge Text
( Question the password ) Information elements
. FCS(CRC): Include 32 Bit cyclic redundancy check (CRC), For error detection , Note that error detection is not error correction

3 : Data frame

0x2: Data frame protocol format

The form of the data frame depends on the form of the network . What kind of frame does it belong to , It all depends on subtype( subtypes ) position , It has nothing to do with whether other bits appear in the frame

The form of the data frame depends on the form of the network . What kind of frame does it belong to , It all depends on subtype( subtypes ) position , It has nothing to do with whether other bits appear in the frame

(IBSS A kind of data frame )

( The access point sends (From AP) Frame of , A kind of data frame )

( To the access point (To AP) Frame of , A kind of data frame )

(WDS frame , A kind of data frame )

. Frame control structure (Frame Control)
) Protocol Version: ( Protocol version ) Usually it is 0
) Type: The frame type , Data frame :
) Subtype: Further determine the sub type of the frame , The format of this field is different for different types of data frames
3.1) IBSS frame
3.1.) : Data
3.1.) : Null
3.2) From AP frame
3.2.) : Data
3.2.) : Data+CF+ASK
3.2.) : Data+CF+Poll
3.2.) : Data+CF+ACK+CF+Poll
3.2.) : CF+ACK
3.2.) : CF+Poll
3.2.) : ACK+CF+Poll
3.3) To AP frame
3.3.) : Data
3.3.) : Data+CF+ACK
3.3.) : Null
3.3.) : CF+ACK(no data)
3.4) WDS frame
null
) To DS: Indicates whether the frame is BSS towards DS When sending a frame
4.1) IBSS: Set to 0
4.2) To AP: Set to 1
4.3) From AP: Set to 0
4.4) WDS: Set to 1
) From DS: Indicates whether the frame is DS towards BSS When sending a frame
5.1) IBSS: Set to 0
5.2) To AP: Set to 0
5.3) From AP: Set to 1
5.4) WDS: Set to 1
) More Fragment: It is used to describe the case that a long frame is segmented , Is there any other frame , If so, the value is set to 1
) Retry( Retransmission domain ): Indicates that the segment is a retransmission frame of the previous transmission segment .
) Power Management: After the frame is transmitted , Power management mode adopted by the station
8.1) by 1: STA be in power_save Pattern
8.2) by 0: STA be in active Pattern
) More Data: It means that many frames are cached in the station . That is, there is at least one data frame to send to STA Is set to 1.
) Protected Frame: Express basis WEP(Wired Equivalent Privacy) The algorithm encrypts the main frame . If the body part of the frame contains the data processed by the key set , Is set to 1, Otherwise set to 0
) Order( Serial number field ): In long frame segment transmission , The domain is set to 1 Indicates that the receiver should process the frame in strict order , Otherwise set to 0
. Duration/ID( The duration of the / identification )
Indicates how long the frame and its acknowledgement frame will occupy the channel ,Duration The value is used for the network assignment vector (NAV) Calculation
. Address Fields( Address field ):
The specific format of this field depends on the subtype of the control frame , There are some slight differences between different subtypes
) IBSS
1.1) Destination Address
1.2) Source Address
1.3) BSSID
Every BSS Will be given a BSSID, It's a length of 48 individual bit The binary ID of , Used to identify different BSS
) From AP
2.1) Destination Address
2.2) BSSID
2.3) Source Address
) To AP
3.1) BSSID
3.2) Source Address
3.3) Destination Address
) WDS
4.1) BSSID
4.2) Source Address
4.3) Destination Address
. Sequence Control( Sequence control domain ): Used to filter duplicate frames
) MSDU(MAC Server Data Unit), 12 A serial number (Sequence Number)
) MMSDU(MAC Management Server Data Unit), 4 Bit segment number (Fragment Number) form
[SA, Only WDS The frame in has this field ]
. Frame Body(Data): Information sent or received .
. FCS(CRC): Include 32 Bit cyclic redundancy check (CRC), For error detection , Note that error detection is not error correction

0x3:  Control frame protocol format

(RTS frame , A kind of control frame )

(CTS frame , A kind of control frame )

(ACK frame , A kind of control frame )

(PS-Poll frame )

. Frame control structure (Frame Control)
) Protocol Version: ( Protocol version ) Usually it is 0
) Type: The frame type , Control frame :
) Subtype: Further determine the sub type of the frame :
Control frame
3.1) Request to send (Request To Send,RTS) Data packets
3.2) Clear send (Clear To Send,CTS) Data packets
Data frame
3.3) ACK confirm (RTS/CTS)
3.4) PS-Poll: When a mobile workstation wakes up from power saving mode , Will send a PS-Poll Frame to base station , To get any temporary frames
) To DS: Indicates that the frame is BSS towards DS When sending a frame , The value is set to 1
) From DS: Indicates that the frame is DS towards BSS When sending a frame , The value is set to 1
The control frame handles access to the wireless media , So it can only be generated by a wireless workstation . The transmission system does not receive control frames , So these two Bit Necessary for 0
) More Fragment: It is used to describe the case that a long frame is segmented , Is there any other frame , If so, the value is set to 1.
The control frame cannot be cut , This Bit Necessary for 0
) Retry( Retransmission domain ): Indicates that the segment is a retransmission frame of the previous transmission segment .
Control frames are not like management or data frames , Must wait in the sequence for resend , So the Bit Necessary for 0
) Power Management: After the frame is transmitted , Power management mode adopted by the station
8.1) by 1: STA be in power_save Pattern
8.2) by 0: STA be in active Pattern
) More Data: It means that many frames are cached in the station . That is, there is at least one data frame to send to STA Is set to 1.
More Data bit Only for managing data frames , In the control frame, this Bit Necessary for 0
) Protected Frame: Express basis WEP(Wired Equivalent Privacy) The algorithm encrypts the main frame . If the body part of the frame contains the data processed by the key set , Is set to 1, Otherwise set to 0.
The control frame is not encrypted . So for the control frame ,Protected Frame bit Necessary for 0.
) Order( Serial number field ): In long frame segment transmission , The domain is set to 1 Indicates that the receiver should process the frame in strict order , Otherwise set to 0.
The control frame is the basic frame exchange program (atomic frame exchange operation) The constituent elements of , So it has to be sent in order . So this Bit Necessary for 0
. Duration/ID( The duration of the / identification )
Indicates how long the frame and its acknowledgement frame will occupy the channel ,Duration The value is used for the network assignment vector (NAV) Calculation .
Be careful : stay PS-Poll The frame does not contain Duration/ID This field
. Address Fields( Address field ):
The specific format of this field depends on the subtype of the control frame , There are some slight differences between different subtypes
3.1) RTS( Request to send frame )
3.1.) Receiver Address( Receiver address )
The address of the workstation receiving the large frame
3.1.) Transmitter Address( Sender address )
RTS The address of the sender of the frame
3.2) CTS( Allow to send )
3.2.) Receiver Address( Receiver address )
3.3) ACK( The reply )
3.3.) Receiver Address( Receiver address )
3.4) PS-Poll( Power saving mode one polling )
3.4.) AID( Connection ID association ID)
The connection ID is a value specified by the access point , To distinguish between connections . Put this ID into the frame , Access points can be found for their ( Mobile workstation ) The frames stored
3.4.) BSSID
This bit contains the current location of the sender BSS(AP) Of BSSID , this BSS Set up from the currently connected AP
3.4.) Transmitter Address( Sender address )
This is a PS-Poll At the sending end of the frame MAC Address
. FCS(CRC): Include 32 Bit cyclic redundancy check (CRC), For error detection , Note that error detection is not error correction

Wi-Fi The authentication process

With 802.11 After the basic format of the agreement , We can use wireshark Carry out the bag grabbing experiment , Test our theory

ifconfig -a
ifconfig wlan1 up
airmon-ng start wlan1
start-up wireshark, choice mon0 network card ( Open the Monotor Virtual network card of mode

0x1: Ordinary non encrypted connection process

1. AP send out Beacon Broadcast management frame

because AP Send this Beacon The management frame packet is the broadcast address , So our PCMIA Built in network card 、 perhaps USB The external network card will receive this packet , And then in our " Wireless connection list " It shows

2. The client specifies to the bearer SSID Of AP send out Probe Request( Detection request ) frame

When we click " Connect " When , The wireless network card will send a Prob Data frame , Used to direct to AP Request connection

3. AP Access point to client SSID Answer the connection request

AP Responded to the client's connection , And said not to accept any form of " Frame payload encryption (frame-payload-encryption)"

4. Client to target AP Request authentication (Authentication)

5. AP Authentication of the client (Authentication) Ask for a response

AP Respond , Means to receive authentication

6. Client to AP Send connection (Association) request

After the authentication is passed , All the preparatory work has been done , At this time, the client can send WLAN AP Initiate a formal connection request , Request access to WLAN

7. AP To connect (Association) Request a response

AP Connection requests to clients (Association) Responded ( Include SSID、 performance 、 Encryption settings, etc ). thus ,Wi-Fi The connection authentication interaction is all over , After that, the data can be sent normally

8. Client to AP Request disconnect (Disassociation)

When we click " disconnect " When , The network card will send AP Send a disconnected management data frame , Request to disconnect

thus , We can find out , Based on the understanding of data frame format , Hackers can launch attacks against protocols

1. Deanthentication attack 
2. Disassociation attack

Hackers can use this method to speed up the detection of WEP/WPS-PSK Protected WLAN attacks , Force the client to reconnect and produce ARP Traffic ( be based on WEP The attack of )、 Or capture again WPA Four handshakes of connection , Then we can attack the password by offline dictionary or rainbow table cracking

0x2: be based on WEP Encrypted connection process

0x3: be based on WPA-PSK Encrypted connection process

In principle, these two kinds of connection and interaction processes are similar to those without encryption ( Open system approach ) identical , Interested friends can use wireshark Carry out the bag grabbing experiment

Reference resources

Wireshark 802.11 Display Filter Field Reference : http://www.willhackforsushi.com/papers/80211_Pocket_Reference_Guide.pdf

Read wireless security quickly : http://www.freebuf.com/articles/wireless/112221.html#

802.11 Protocol frame format 、Wi-Fi Connection interaction process 、 Introduction to wireless cracking : http://www.cnblogs.com/LittleHann/p/3700357.html

Xiamen lighting future network technology Co., Ltd , It is the best wechat application in Xiamen , Applet , Wechat website , Official account development company

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