帧间间隔（IFS: interframe space）
1.广播帧 beacon frame 发送
The AP is periodically transmitting (broadcasting) a special signal called Beacon signal saying "I am here.. I am here .. I am capable of this and that .. etc)". Basically this Beacon is like MIB/SIB + Physical Layer Sync channel in mobile communication (e.g, WCDMA/LTE etc). AP broadcast this Beacon several times per seconds. Beacon transmission interval is contained in one of Beacon information fields. (See Beacon data field)
2.解码广播帧beacon 建立无线信号同步 无线认证和连接，接收注册流程
the device first detect and decode this beacon signal and establish physical synchronization.
After the physical Sync get established, the device and WLAN network goes through the authentication process and then association process which is similar concept to the registration process in mobile phone communication
< Step 1 >
< Step 2 >
< Step 3 >
< Step 4 >
< Step 5 >
< Step 6 >
< Step 7 >
< Step 8 >
< Step 9 >
< Step 10 >
< Step 11 >
< Step 12 >
数据发送和接收流程
More detailed process of this data tranmission in terms of timing can be illustrated as shown below.
i) Source transmit the short RTS burst which carries source, destination and duration of following transaction.
ii) All other devices around the source may receive the RTS burst. They are all checking if the RTS is for itself or not.
iii) If it is for itself and the medium is free, the destination device transmit the CTS which also carries the duration of following transaction.
iv) Now all the other device (the neighbouring device other than 'Destination' device) also knows that the medium will be occupied for a certain time from now, they would set their NAV(Network Allocation Vector) accordingly so that it would not try sensing and try to transmit anything during that period.
In case of Fragmented Frame, the sequence goes as follows :
Sleeping Mode and Data Transmission
帧间隔：
1、SIFS：短帧间间隔
SIFS是最短的时间区段，用来间隔需要立即响应的帧，如控制帧（RTS/CTS/ACK）等。在帧交换顺序地两次传输之间使用最短间隔，可以防止其它正在等待介质的站点试图使用介质。
2、PIFS：集中协调功能帧间间隔，只能够由工作于PCF模式的站点来使用。
3、DIFS：分布协调功能帧间间隔，只能够由工作于DCF模式的站点来使用。
4、EIFS: 在前一帧出错的情况下，发送节点 不得不延迟 EIFS 而不是DIFS时间段，再发送下一帧。
